Thursday.
1405.6710
Tracing the cosmic velocity field at z~0.1 from galaxy luminosities in the SDSS DR7
Feix, Nusser, Branchini
Probe the cosmic peculiar velocity field out to z~0.1 using spatial modulations in the distribution of observed luminosities, from 5e5 galaxies from SDSS DR7. r-band LF well represented by a Schechter form. Bulk flows and higher velocity moments in two z bins, 0.02<z<0.07 and 0.07<z<0.22, agree with the predictions of the LCDM model. Estimate sigma_8~1.1pm0.4 for the amplitude of the linear matter PS (low accuracy due to small number of galaxies). While the low-z bin is robust against coherent photometric uncertainties, the bias of results from the second bin is consistent with the ~1% magnitude tilt reported by the SDSS collaboration. The systematics are expected to have a significantly lower impact in future datasets with larger sky coverage and better photometric calibration.
1405.6711
Offset active galactic nuclei as tracers of galaxy mergers and supermassive black hole growth
Comerford, Greene
Offset AGNs are AGNs that are in ongoing galaxy mergers, which produce kinematic offsets in the AGNs relative to their host galaxies. Offset AGNs are also close relatives of dual AGNs. Conduct a systematic search for offset AGNs in SDSS by selecting AGN emission lines that exhibit statistically significant LoS velocity offsets relative to systemic. From a parent sample of 18k Type 2 AGNs at z<0.21, identify 351 offset AGN candidates with velocity offsets of 50 km/s<{v} < 410 km/s. When accounted for projection effects in the observed velocities, estimate that 4-8% of AGNs are offset AGNs. Design selection criteria to bypass velocity offsets produced by rotation gas disks, AGN outflows, and gravitational recoil of SN BHs, but follow-up observations are still required to confirm candidates as offset AGNs. Find that the fraction of AGNs that are offset candidates increases with AGN bolometric luminosity, from 0.7% to 6% over the luminosity range 43 < log(L_bol)[erg/s]<46. If these candidates are shown to be bona mice offset AGNs, then this would be direct observational evidence that galaxy mergers preferentially trigger high-luminosity AGNs. Finally, find that the fraction of AGNs that are offset AGN candidates increases from 1.9% at z=0.1 to 32% at z=0.7, in step with the growth in the galaxy merger fraction over the same z range.
Friday, May 30, 2014
Tuesday, May 27, 2014
Day 666
Tuesday.
1405.6237
Characterizing the galactic warp with Gaia: I. the tilted ring model with a twist
Abedi, Mateu, Aguilar, Figueras, Romero-Gomez
Explore the possibility of detecting and characterizing the warp of the stellar disk of MW using synthetic Gaia data. The availability of proper motions and, for the brightest stars radial velocities, adds a new dimension to this study. A family of Great Circle Cell Counts (GC3) methods is used. They are ideally used to find the tilt and twist of a collection of rings, which allow us to detect and measure the warp parameters. To test them, use random realizations of test particles which evolve in a realistic Galactic potential warped adiabatically to various final configurations. In some cases, a twist is introduced additionally. The Gaia selection function, its errors model and a realistic 3d extinction map are applied to mimic 3 tracer populations: OB, A and Red Clump stars. Show how the use of kinematics improves the accuracy in the recovery of the warp parameters. The OB stars are demonstrated to be the best tracers [why?] determining the tilt angle with accuracy better than ~0.5 up to Galctocentric distance of ~16 kpc. Using data with good astrometric quality, the same accuracy is obtained for A type stars up to ~13 kpc and for Red Clump up to the expected stellar cut-off. Using OB stars the twist angle is recovered to within <3deg for all distances.
1405.6336
The origins and concentrations of water, carbon, nitrogen and noble gases on Earth
Marty
They sot pic compositions of terrestrial H and N are clearly different from those of the nebular gas from which the solar system formed, and also differ from most of cometary values. Terrestrial N and H isotopic compositions are in the range of values characterizing primitive meteorites, which suggests that H2O, N and other volatile elements on Earth originated from a cosmochemical reservoir that also sourced the parent bodies of primiteve meteorites. Remnants of the proto-solar nebula (PSN) are still present in the mantle, presumably signing the sequestration of PSN gas at an early stage of planetary growth. The contribution of cometary volatiles appears limited to a few percents at most of the total volatile inventory of the Earth. The isotope signatures of H, N, Ne and Ar can be explained by mixing between two end-members of solar and chondritic compositions, respectively, and do not require isotropic fractionation during hydrodynamic escape of an early atmosphere. The terrestrial inventory of 40Ar (produced by the decay of 40K throughout the Earth's history) suggests that a significant fraction of radiogenic Ar may be still trapped in the silicate Earth. By normalizing other volatile element abundances to this isotope, it is proposed that the Earth is not as volatile-poor as previously thought. Our planet may indeed contain up to ~3000 ppm H2O (preferred range: 1000-3000 ppm), and up to ~500 ppm C, both largely sequestrated in the solid Earth. This volatile content is equivalent to a ~2 (pm1)% contribution of carbonaceous chondrite (Cl-CM) material to a dry proto-Earth, which is higher than the contribution of chondritic material advocated to account for the platinum group element budget of the mantle. Such a (relatively) high contribution of volatile-rich matter is consistent with the accretion of a few wet planetesimals during Earth accretion.
1405.6568
Lensing reconstruction from a patchwork of polarization maps
Namikawa, Nagata
The lensing signals imvolved in CMB polarization maps have already been measured with ground-based experiments such as SPTpol and POLARBEAR, and would become important as a probe of cosmological and astrophysical issues in the near future. Sizes of polarization maps from ground-based experiments are, however, limited by contamination of long wavelength modes of observational noise. To further extract the lensing signals, explore feasibility of measuring lensing signals from a collection of small sky maps each of which is observed separately by a ground-based large telescope, i.e., lensing reconstruction from a patchwork map of large sky coverage organized from small sky patches. Show that, although the B-mode PS obtained from the patchwork map is biased due to baseline uncertainty, bias on the lensing potential would be negligible if the B-mode on scales larger than the blowup scale of 1/f noise is removed in the lensing reconstruction. As examples of cosmological applications, also show 1) the cross-correlations between the reconstructed lensing potential and full-sky temperature/polarization maps from satellite missions such as PLANCK and LiteBIRD, and 2) the use of the reconstructed potential for delousing B-mode polarization of LiteBIRD observation.
1405.6701
Warming early Mars with CO2 and H2
Ramirez et al
Early Mars had flowing water, current Mars is below freezing temperature. The above freezing temperatures required to explain valley formation could have been transient, in response to frequent large meteorite impacts on early Mars, or they could have been caused by long-lived greenhouse warming. Climate models that consider only the greenhouse gases CO2 and H2O vapor have been unable to recreate warm surface conditions, given the lower solar luminosity at that time. Use 1d climate model to demonstrate that an atmosphere containing 1.3-4 bar of CO2 and H2O vapor, along with 5 to 20% H2, could have raised the mean surface temperature of early mars above the freezing point of water. Vigorous volcanic outgassing from a highly reduced early martian mantle is expected to provide sufficient atmospheric H2 and CO2, the latter from the photochecmial oxidation of outgassed CH4 and CO, to form a CO2-H2 greenhouse. Such a dense early martian atmosphere is consistent with independent estimates of surface pressed based on cratering data.
1405.6237
Characterizing the galactic warp with Gaia: I. the tilted ring model with a twist
Abedi, Mateu, Aguilar, Figueras, Romero-Gomez
Explore the possibility of detecting and characterizing the warp of the stellar disk of MW using synthetic Gaia data. The availability of proper motions and, for the brightest stars radial velocities, adds a new dimension to this study. A family of Great Circle Cell Counts (GC3) methods is used. They are ideally used to find the tilt and twist of a collection of rings, which allow us to detect and measure the warp parameters. To test them, use random realizations of test particles which evolve in a realistic Galactic potential warped adiabatically to various final configurations. In some cases, a twist is introduced additionally. The Gaia selection function, its errors model and a realistic 3d extinction map are applied to mimic 3 tracer populations: OB, A and Red Clump stars. Show how the use of kinematics improves the accuracy in the recovery of the warp parameters. The OB stars are demonstrated to be the best tracers [why?] determining the tilt angle with accuracy better than ~0.5 up to Galctocentric distance of ~16 kpc. Using data with good astrometric quality, the same accuracy is obtained for A type stars up to ~13 kpc and for Red Clump up to the expected stellar cut-off. Using OB stars the twist angle is recovered to within <3deg for all distances.
1405.6336
The origins and concentrations of water, carbon, nitrogen and noble gases on Earth
Marty
They sot pic compositions of terrestrial H and N are clearly different from those of the nebular gas from which the solar system formed, and also differ from most of cometary values. Terrestrial N and H isotopic compositions are in the range of values characterizing primitive meteorites, which suggests that H2O, N and other volatile elements on Earth originated from a cosmochemical reservoir that also sourced the parent bodies of primiteve meteorites. Remnants of the proto-solar nebula (PSN) are still present in the mantle, presumably signing the sequestration of PSN gas at an early stage of planetary growth. The contribution of cometary volatiles appears limited to a few percents at most of the total volatile inventory of the Earth. The isotope signatures of H, N, Ne and Ar can be explained by mixing between two end-members of solar and chondritic compositions, respectively, and do not require isotropic fractionation during hydrodynamic escape of an early atmosphere. The terrestrial inventory of 40Ar (produced by the decay of 40K throughout the Earth's history) suggests that a significant fraction of radiogenic Ar may be still trapped in the silicate Earth. By normalizing other volatile element abundances to this isotope, it is proposed that the Earth is not as volatile-poor as previously thought. Our planet may indeed contain up to ~3000 ppm H2O (preferred range: 1000-3000 ppm), and up to ~500 ppm C, both largely sequestrated in the solid Earth. This volatile content is equivalent to a ~2 (pm1)% contribution of carbonaceous chondrite (Cl-CM) material to a dry proto-Earth, which is higher than the contribution of chondritic material advocated to account for the platinum group element budget of the mantle. Such a (relatively) high contribution of volatile-rich matter is consistent with the accretion of a few wet planetesimals during Earth accretion.
1405.6568
Lensing reconstruction from a patchwork of polarization maps
Namikawa, Nagata
The lensing signals imvolved in CMB polarization maps have already been measured with ground-based experiments such as SPTpol and POLARBEAR, and would become important as a probe of cosmological and astrophysical issues in the near future. Sizes of polarization maps from ground-based experiments are, however, limited by contamination of long wavelength modes of observational noise. To further extract the lensing signals, explore feasibility of measuring lensing signals from a collection of small sky maps each of which is observed separately by a ground-based large telescope, i.e., lensing reconstruction from a patchwork map of large sky coverage organized from small sky patches. Show that, although the B-mode PS obtained from the patchwork map is biased due to baseline uncertainty, bias on the lensing potential would be negligible if the B-mode on scales larger than the blowup scale of 1/f noise is removed in the lensing reconstruction. As examples of cosmological applications, also show 1) the cross-correlations between the reconstructed lensing potential and full-sky temperature/polarization maps from satellite missions such as PLANCK and LiteBIRD, and 2) the use of the reconstructed potential for delousing B-mode polarization of LiteBIRD observation.
1405.6701
Warming early Mars with CO2 and H2
Ramirez et al
Early Mars had flowing water, current Mars is below freezing temperature. The above freezing temperatures required to explain valley formation could have been transient, in response to frequent large meteorite impacts on early Mars, or they could have been caused by long-lived greenhouse warming. Climate models that consider only the greenhouse gases CO2 and H2O vapor have been unable to recreate warm surface conditions, given the lower solar luminosity at that time. Use 1d climate model to demonstrate that an atmosphere containing 1.3-4 bar of CO2 and H2O vapor, along with 5 to 20% H2, could have raised the mean surface temperature of early mars above the freezing point of water. Vigorous volcanic outgassing from a highly reduced early martian mantle is expected to provide sufficient atmospheric H2 and CO2, the latter from the photochecmial oxidation of outgassed CH4 and CO, to form a CO2-H2 greenhouse. Such a dense early martian atmosphere is consistent with independent estimates of surface pressed based on cratering data.
Monday, May 26, 2014
Day 665
Monday.
1405.5885
Velocity bias in the distribution of dark matter haloes
Baldauf, Desjacques, Seljak
The standard formalism for the co-evolution of haloes and DM predicts that any initial halo velocity bias rapidly decays to zero. Argue that, when the purpose is to compute statistics like power spectra etc., the coupling in the momentum conservation equation for the biased tracers must be modified. New formulation predicts the constancy in time of any statistical halo velocity bias present in the initial conditions, in agreement with peak theory. Test this prediction by studying the evolution of a conserved halo population in N-body simulations. Establish that the initial simulated halo density and velocity statistics show distinct fixtures of the peak model and, thus, deviate from the simple local Lagrangian bias. Demonstrate, for the first time, that the time evolution of their velocity is in tension with the rapid decay expected in the standard approach.
1405.5888
Cosmological constraints from the CFHTLenS shear measurements using a new, accurate and flexible way of predicting nonlinear mass clustering
Angulo, Hilbert
Explore the cosmological constraints from cosmic shear using a new way of modeling the NL matter correlation functions. The new formalism extends the method of Angulo&White(2010), which manipulates outputs of N-body sims to represent the 3d NL mass distribution in different cosmological scenarios. Show that predictions from the approach for shear 2-pt correlations at 1 to 300 arcmin separations are accurate at the 10% level, even for extreme changes in cosmology. For moderate changes, with target cosmologies similar to that preferred by analyses of recent Planck data, the accuracy is close to 5%. Combine this approach with a MCMC sampler to explore constraints on a LCDM model from the shear correlation functions measured in the CFHTLenS. Obtain constraints on the parameter combination sigma_8(Omega_m/0.27)^0.6=0.80pm0.3. Combined with results from CMB data, obtain marginalized constraints on sigma_8=0.81 and Omega_m=0.29. These results are fully compatible with previous analyses, which supports the validity of the approach. Discuss the advantages of the method and the potential it offers, including a path to incorporate in detail the effects of baryons, among other effects, in future high-precision cosmological analysis.
1405.5885
Velocity bias in the distribution of dark matter haloes
Baldauf, Desjacques, Seljak
The standard formalism for the co-evolution of haloes and DM predicts that any initial halo velocity bias rapidly decays to zero. Argue that, when the purpose is to compute statistics like power spectra etc., the coupling in the momentum conservation equation for the biased tracers must be modified. New formulation predicts the constancy in time of any statistical halo velocity bias present in the initial conditions, in agreement with peak theory. Test this prediction by studying the evolution of a conserved halo population in N-body simulations. Establish that the initial simulated halo density and velocity statistics show distinct fixtures of the peak model and, thus, deviate from the simple local Lagrangian bias. Demonstrate, for the first time, that the time evolution of their velocity is in tension with the rapid decay expected in the standard approach.
1405.5888
Cosmological constraints from the CFHTLenS shear measurements using a new, accurate and flexible way of predicting nonlinear mass clustering
Angulo, Hilbert
Explore the cosmological constraints from cosmic shear using a new way of modeling the NL matter correlation functions. The new formalism extends the method of Angulo&White(2010), which manipulates outputs of N-body sims to represent the 3d NL mass distribution in different cosmological scenarios. Show that predictions from the approach for shear 2-pt correlations at 1 to 300 arcmin separations are accurate at the 10% level, even for extreme changes in cosmology. For moderate changes, with target cosmologies similar to that preferred by analyses of recent Planck data, the accuracy is close to 5%. Combine this approach with a MCMC sampler to explore constraints on a LCDM model from the shear correlation functions measured in the CFHTLenS. Obtain constraints on the parameter combination sigma_8(Omega_m/0.27)^0.6=0.80pm0.3. Combined with results from CMB data, obtain marginalized constraints on sigma_8=0.81 and Omega_m=0.29. These results are fully compatible with previous analyses, which supports the validity of the approach. Discuss the advantages of the method and the potential it offers, including a path to incorporate in detail the effects of baryons, among other effects, in future high-precision cosmological analysis.
Sunday, May 25, 2014
Day 664
Saturday, Sunday.
1401.7328
From voids to Coma: the prevalence of pre-processing in the local Universe
Cybulski et al
Quantify the degree to which SF activity is quenched as a function of environment: examine the effects of pre-processing across the Coma Supercluster, including 3505 galaxies over 500 sq deg. Vornoi Tesselation to characterize density field, and Minimal Spanning Tree to define continuous structures. Environment = cluster, group, filament, and void; quantify the degree to which environment contributes to quenching of SF activity. Sample covers over two orders of magnitude in stellar mass (1e8.5 to 11 Msun), and consequently trace the effects of environment on SF activity for dwarf and massive galaxies, distinguishing so-called "mass quenching" from "environment quenching". Environmentally-driven quenching of SF activity, measured relative to the void galaxies, occurs to progressively greater degrees in filaments, groups, and clusters, and this trend holds for dwarf and massive galaxies alike. A similar trend is found using g-r colors, but with a more significant disparity between galaxy mass bins driven by increased internal dust extinction in massive galaxies. The SFR distributions of massive SF galaxies have no significant environmental dependence, but the distributions for dwarf SF galaxies are found to be statistically distinct in most environments. Pre-processing plays a significant role at low redshift, as environmentally-driven galaxy evolution affects nearly half of the galaxies in the group environment, and a significant fraction of the galaxies in the more diffuse filaments. Study underscores the need for sensitivity to dwarf galaxies to separate mass-driven from environmentally-driven effects, and the use of unbiased tracers of SF activity.
1401.7329
Stellar mass -- halo mass relation and star formation efficiency in high-mass halos
Kravtsov, Vikhlinin, Meschscheryakov
Compare stellar and halo mass: M* from optical and IR data, and total mass from X-ray observations. Find that stellar mass of BCGs scales as M500^a_BCG with a_BCG~0.35pm0.1 and scatter of M*BCG at a fixed M500 of ~0.2 dex. Show that M*-M relations from abundance matching or halo modeling reported in recent studies underestimate stellar masses of BCGs by a factor of ~2-4, because these studies used stellar mass functions based on photometry that severely underestimates the outer surface brightness profiles of massive galaxies. Show that M*-M relation derived using abundance matching with the recent SMF calibration by Bernardi+2013 based on improved photometry is in a much better agreement with the relation with the derived relation here. The total stellar mass of galaxies correlates with total mass M500 with the slope of approximately 0.6pm0.1 and scatter of 0.1 dex. This indicates that efficiency with which baryons are converted into stars decreases with increasing cluster mass. Show that for a fixed choice of the IMF the total stellar fraction in clusters is only a factor of ~3-5 lower than the peak stellar fraction reached in M~1e12 Msun halos, and only a factor of ~1.5-3 if the IMF becomes progressively more bottom heavy with increasing mass in early type galaxies, as indicated by recent observations. The larger normalization and slope of the M*-M relation derived in this study shows that the overall efficiency of SF in massive haloes is suppressed much less than was thought before and that feedback and associated suppression of SF in massive haloes should be weaker than assumed in most of the current SAM and simulations.
1407.7331
Galaxy and mass assembly (GAMA): fine filaments of galaxies detected within voids
Alpaslan, et al
Based on GAMA, report discovery of structures that are 'tendrils' of galaxies: coherent, thin chains of galaxies that are rooted in filaments and terminate in neighboring filaments or voids. On average, tendrils contain 6 galaxies and span 10 Mpc/h. Use the so-called line correlation function to prove that tendrils represent real structures rather than accidental alignments. Show that voids found in DR7 survey that overlap with GAMA contain a large number of galaxies, primarily belonging to tendrils. This implies that void sizes are strongly dependent on the number density and sensitivity limits of a survey. Caution that galaxies in low density regions, that may be defined as 'void galaxies', will have local galaxy number densities that depend on such observational limits and are likely higher than can be directly measured.
1401.7657
Analytical model for non-thermal pressure in galaxy clusters
Shi, Komatsu
Non-thermal pressure in the intracluster gas has been found ubiquitously in numerical simulations, and observed indirectly. In this paper, develop an analytical model for intracluster non-thermal pressure. Write down and solve a first-order differential equation describing the evolution of non-thermal velocity dispersion. This equation is based on insights gained from observations, numerical simulations, and theory of turbulence. The non-thermal energy is sourced, in a self-similar fashion, by the mass growth of clusters via mergers and accretion, and dissipates with a time scale determined by the turnover time of the largest turbulence eddies. Model predicts a radial profile of non-thermal pressure for relaxed clusters. The non-thermal fraction increases with radius, redshift, and cluster mass, in agreement with numerical simulations. The radial dependence is due to a rapid increase of the dissipation time scale with radii, and the mass and redshift dependence comes from the mass growth history. Combining model for the non-thermal fraction with the Komatsu-Seljak model for the total pressure, obtain thermal and non-thermal pressure profiles, and compute the hydrostatic mass bias. Find typically 10% bias for the hydrostatic mass enclosed within r500.
1401.7669
A panchromatic analysis of starburst galaxy M82: probing the dust properties
Hutton et al
Combine NUV, optical and IR imaging of M82 to explore the properties of dust both in the ISM of the galaxy and the dust entrained in the superwind. The three NUV filters of Swift/UVOT enable detail probing of the properties of the extinction curve in the region around the 2175A bump. The NUV color-color diagram strongly rules out a Calzetti-type law, which can either reflect intrinsic changes in the dust properties or in the SFH compared to starbursts well represented by such an attenuation law. Emphasize that it is mainly in the NUV region where a standard MW-type law is preferred over a Calzetti law. The age and dust distribution of the stellar populations is consistent with the scenario of an encounter with M81 in the recent 400 Myr. The radial gradients of the NUV and optical colors in the super wind region support the hypothesis that the emission in the wind cone is driven by scattering from dust grains entrained in the ejecta. The observed wavelength dependence reveals either a grain size distribution $n(a)\propto a^-2.5, where a is the size of the grain, or a flatter distribution with a maximum size cutoff, suggesting that only small grains are entrained in the SNe-driven wind.
1401.7878
A new method for classifying galaxy SEDs from multi-wavelength photometry
Wild et al
From optical-NIR SEDs of galaxies, a new method to classify them using 3 shape parameters (super-colors) based on PCA of model SEDs. As well as cleanly separating a tight red-sequence from star-forming galaxies, 3 unusual populations are identifiable by their unique colors: very dusty SF galaxies with high metallicity and old mean stellar age; post-starburst galaxies which have formed greater than around 10% of their mass in a recent unsustained SB event; and metal-poor quiescent dwarf galaxies. Find that quiescent galaxies account for 45% of galaxies with log(M*/Msun)>11, declining steadily to 13% at log (M*/Msun)=10. The properties and mass-function of the post-starburst galaxies are consistent with a scenario in which gas-rich mergers contribute to the growth of the low and intermediate mass range of the red sequence.
1401.7328
From voids to Coma: the prevalence of pre-processing in the local Universe
Cybulski et al
Quantify the degree to which SF activity is quenched as a function of environment: examine the effects of pre-processing across the Coma Supercluster, including 3505 galaxies over 500 sq deg. Vornoi Tesselation to characterize density field, and Minimal Spanning Tree to define continuous structures. Environment = cluster, group, filament, and void; quantify the degree to which environment contributes to quenching of SF activity. Sample covers over two orders of magnitude in stellar mass (1e8.5 to 11 Msun), and consequently trace the effects of environment on SF activity for dwarf and massive galaxies, distinguishing so-called "mass quenching" from "environment quenching". Environmentally-driven quenching of SF activity, measured relative to the void galaxies, occurs to progressively greater degrees in filaments, groups, and clusters, and this trend holds for dwarf and massive galaxies alike. A similar trend is found using g-r colors, but with a more significant disparity between galaxy mass bins driven by increased internal dust extinction in massive galaxies. The SFR distributions of massive SF galaxies have no significant environmental dependence, but the distributions for dwarf SF galaxies are found to be statistically distinct in most environments. Pre-processing plays a significant role at low redshift, as environmentally-driven galaxy evolution affects nearly half of the galaxies in the group environment, and a significant fraction of the galaxies in the more diffuse filaments. Study underscores the need for sensitivity to dwarf galaxies to separate mass-driven from environmentally-driven effects, and the use of unbiased tracers of SF activity.
1401.7329
Stellar mass -- halo mass relation and star formation efficiency in high-mass halos
Kravtsov, Vikhlinin, Meschscheryakov
Compare stellar and halo mass: M* from optical and IR data, and total mass from X-ray observations. Find that stellar mass of BCGs scales as M500^a_BCG with a_BCG~0.35pm0.1 and scatter of M*BCG at a fixed M500 of ~0.2 dex. Show that M*-M relations from abundance matching or halo modeling reported in recent studies underestimate stellar masses of BCGs by a factor of ~2-4, because these studies used stellar mass functions based on photometry that severely underestimates the outer surface brightness profiles of massive galaxies. Show that M*-M relation derived using abundance matching with the recent SMF calibration by Bernardi+2013 based on improved photometry is in a much better agreement with the relation with the derived relation here. The total stellar mass of galaxies correlates with total mass M500 with the slope of approximately 0.6pm0.1 and scatter of 0.1 dex. This indicates that efficiency with which baryons are converted into stars decreases with increasing cluster mass. Show that for a fixed choice of the IMF the total stellar fraction in clusters is only a factor of ~3-5 lower than the peak stellar fraction reached in M~1e12 Msun halos, and only a factor of ~1.5-3 if the IMF becomes progressively more bottom heavy with increasing mass in early type galaxies, as indicated by recent observations. The larger normalization and slope of the M*-M relation derived in this study shows that the overall efficiency of SF in massive haloes is suppressed much less than was thought before and that feedback and associated suppression of SF in massive haloes should be weaker than assumed in most of the current SAM and simulations.
1407.7331
Galaxy and mass assembly (GAMA): fine filaments of galaxies detected within voids
Alpaslan, et al
Based on GAMA, report discovery of structures that are 'tendrils' of galaxies: coherent, thin chains of galaxies that are rooted in filaments and terminate in neighboring filaments or voids. On average, tendrils contain 6 galaxies and span 10 Mpc/h. Use the so-called line correlation function to prove that tendrils represent real structures rather than accidental alignments. Show that voids found in DR7 survey that overlap with GAMA contain a large number of galaxies, primarily belonging to tendrils. This implies that void sizes are strongly dependent on the number density and sensitivity limits of a survey. Caution that galaxies in low density regions, that may be defined as 'void galaxies', will have local galaxy number densities that depend on such observational limits and are likely higher than can be directly measured.
1401.7657
Analytical model for non-thermal pressure in galaxy clusters
Shi, Komatsu
Non-thermal pressure in the intracluster gas has been found ubiquitously in numerical simulations, and observed indirectly. In this paper, develop an analytical model for intracluster non-thermal pressure. Write down and solve a first-order differential equation describing the evolution of non-thermal velocity dispersion. This equation is based on insights gained from observations, numerical simulations, and theory of turbulence. The non-thermal energy is sourced, in a self-similar fashion, by the mass growth of clusters via mergers and accretion, and dissipates with a time scale determined by the turnover time of the largest turbulence eddies. Model predicts a radial profile of non-thermal pressure for relaxed clusters. The non-thermal fraction increases with radius, redshift, and cluster mass, in agreement with numerical simulations. The radial dependence is due to a rapid increase of the dissipation time scale with radii, and the mass and redshift dependence comes from the mass growth history. Combining model for the non-thermal fraction with the Komatsu-Seljak model for the total pressure, obtain thermal and non-thermal pressure profiles, and compute the hydrostatic mass bias. Find typically 10% bias for the hydrostatic mass enclosed within r500.
1401.7669
A panchromatic analysis of starburst galaxy M82: probing the dust properties
Hutton et al
Combine NUV, optical and IR imaging of M82 to explore the properties of dust both in the ISM of the galaxy and the dust entrained in the superwind. The three NUV filters of Swift/UVOT enable detail probing of the properties of the extinction curve in the region around the 2175A bump. The NUV color-color diagram strongly rules out a Calzetti-type law, which can either reflect intrinsic changes in the dust properties or in the SFH compared to starbursts well represented by such an attenuation law. Emphasize that it is mainly in the NUV region where a standard MW-type law is preferred over a Calzetti law. The age and dust distribution of the stellar populations is consistent with the scenario of an encounter with M81 in the recent 400 Myr. The radial gradients of the NUV and optical colors in the super wind region support the hypothesis that the emission in the wind cone is driven by scattering from dust grains entrained in the ejecta. The observed wavelength dependence reveals either a grain size distribution $n(a)\propto a^-2.5, where a is the size of the grain, or a flatter distribution with a maximum size cutoff, suggesting that only small grains are entrained in the SNe-driven wind.
1401.7878
A new method for classifying galaxy SEDs from multi-wavelength photometry
Wild et al
From optical-NIR SEDs of galaxies, a new method to classify them using 3 shape parameters (super-colors) based on PCA of model SEDs. As well as cleanly separating a tight red-sequence from star-forming galaxies, 3 unusual populations are identifiable by their unique colors: very dusty SF galaxies with high metallicity and old mean stellar age; post-starburst galaxies which have formed greater than around 10% of their mass in a recent unsustained SB event; and metal-poor quiescent dwarf galaxies. Find that quiescent galaxies account for 45% of galaxies with log(M*/Msun)>11, declining steadily to 13% at log (M*/Msun)=10. The properties and mass-function of the post-starburst galaxies are consistent with a scenario in which gas-rich mergers contribute to the growth of the low and intermediate mass range of the red sequence.
Friday, May 23, 2014
Day 663
Friday.
1405.5527
MITEoR: a scalable interferometer for precision 21 cm cosmology
Zheng, Tegmark, et al
MIT Epoch of Reionization: a pathfinder low-frequency radio interferometer whose goal is to test technologies that improve the calibration precision and reduce the cost of high-sensitivity 3d mapping. MITEoR accomplishes this by using massive baseline redundancy, which enables both automated precision calibration and correlator cost reduction. For an N antenna instrument, the cost scaling is reduced from N^2 to NlogN. Demonstrate and quantify the power and robustness of redundancy for scalability and precision. Find that the calibration parameters precisely describe the effect of the instrument upon the measurements, allowing to form a model that is consistent with chi^2 per DoF<1.2 for as much as 80% of the observations. Use results to develop an optimal estimator of calibration parameters using Wiener filtering, and explore the question of how often and how finely in frequency visibilities must be reliably measured to solve for calibration coefficients. The success of MITEoR with its 64 dual-polarization elements bodes well for the more ambitious Hydrogen Eopch of Reionization Array (HERA) project and other next-generation instruments, which would incorporate many identical or similar technologies using hundreds more antennas, each with dramatically larger collecting area.
1405.5833
Solar system objects as cosmic rays detectors
Privitera, Motloch
In a recent Letter, Jupiter is presented as an efficient detector for UHECRs, through measurement by an Earth-orbiting satellite of gamma rays from UHECRs showers produced in Jupiter's atmosphere Show that this result is incorrect, due to erroneous assumptions on the angular distribution of shower particles. Evaluated other Solar System objects as potential targets for UHECRs detections, and found that the proposed technique is either not viable or not competitive with traditional ground-based UHECRs detectors.
1405.5836
The morphology of galaxies with quiescent recent assembly history in Lambda-CDM universe
Pedrosa et al
Standard disc formation scenario: discs form as the gas cools and flows into the center of the DM halo, conserving the specific angular momentum. Major mergers have been shown to be able to destroy or highly perturb the disc components. More recently, the alignment of the material that is accreted to form the galaxy has been pointed out as a key ingredient to determine galaxy morphology. However, in a hierarchical scenario galaxy formation is a complex process which combiners these processes, and others, in a non-linear way so that the origin of galaxy morphology remains to be fully understood. Aim at exploring the differences in the formation histories of galaxies with a variety of morphology but quite recent merger histories to identify which mechanisms are playing a major role. Analyze when minor mergers could be considered relevant to determine galaxy morphology. Also study the specific angular momentum content of the disc and central spheroidal components, separately. Use cosmological hydrodynamical simulations that include an effective, physically-motivated SN feedback which is able to regulate the SF in hales of different masses. Analyze the morphology and formation history of a sample of 15 galaxies of a cosmological simulation. Perform a spheroid-disc decomposition of the selected galaxies and their progenitor systems. The angular momentum orientation of the merging systems as well as their relative masses are estimated to analyze the role played by orientation and by minor mergers in the determination of the morphology. Find the discs to be formed by conserving the specific angular momentum in accordance with the classical disk formation model. The specific angular momentum of the stellar central spheroid correlates with the DM halo angular momentum determining a power law.
1405.5857
A joint analysis of Planck and BICEP2 B modes including dust polarization uncertainty
Mortonson, Seljak
Analyze BICEP2 and Planck data using a model that includes CMB lensing, gravity waves, and polarized dust. Recently published Planck dust polarization maps have highlighted the difficulty of estimating the amount of dust polarization in low intensity regions, suggesting that the polarization fractions have considerable uncertainties and may be significantly higher than previous predictions. In this paper, do not assume anything about the dust polarization, except for the power spectrum shape, which is taken to be C^{BB,dust}_ell \propto ell^{-2.3}. The resulting joint BICEP2+Planck analysis favors solutions without gravity waves, and the upper limit on the tensor-to-scalar ratio is r<0.11, a slight improvement relative to the Planck analysis alone which gives r<0.13 (95% CL). The estimated amplitude of the dust polarization PS is in rough agreement with expectations for this field based on HI column density. Address the cross-correlation analysis of BICEP2 at 150 GHz with BICEP1 at 100 GHz as a test of FG contamination. Find that the null hypothesis of dust and lensing with r=0 gives Delta chi^2<2 relative to the hypothesis of no dust, so the frequency analysis does not strongly favor either model over the other. Also discuss how Planck dust polarization maps may improve constraints. If the dust polarization is measured perfectly, the limit can reach r<0.05 (or the corresponding detection significance if the observed dust signal plus the expected lensing signal is below the BICEP2 observations), but this degrades quickly to almost no improvement if the dust calibration error is 20% larger or if the Planck dust maps are not processed through the BICEP2 pipeline, including sampling variance noise.
1405.5527
MITEoR: a scalable interferometer for precision 21 cm cosmology
Zheng, Tegmark, et al
MIT Epoch of Reionization: a pathfinder low-frequency radio interferometer whose goal is to test technologies that improve the calibration precision and reduce the cost of high-sensitivity 3d mapping. MITEoR accomplishes this by using massive baseline redundancy, which enables both automated precision calibration and correlator cost reduction. For an N antenna instrument, the cost scaling is reduced from N^2 to NlogN. Demonstrate and quantify the power and robustness of redundancy for scalability and precision. Find that the calibration parameters precisely describe the effect of the instrument upon the measurements, allowing to form a model that is consistent with chi^2 per DoF<1.2 for as much as 80% of the observations. Use results to develop an optimal estimator of calibration parameters using Wiener filtering, and explore the question of how often and how finely in frequency visibilities must be reliably measured to solve for calibration coefficients. The success of MITEoR with its 64 dual-polarization elements bodes well for the more ambitious Hydrogen Eopch of Reionization Array (HERA) project and other next-generation instruments, which would incorporate many identical or similar technologies using hundreds more antennas, each with dramatically larger collecting area.
1405.5833
Solar system objects as cosmic rays detectors
Privitera, Motloch
In a recent Letter, Jupiter is presented as an efficient detector for UHECRs, through measurement by an Earth-orbiting satellite of gamma rays from UHECRs showers produced in Jupiter's atmosphere Show that this result is incorrect, due to erroneous assumptions on the angular distribution of shower particles. Evaluated other Solar System objects as potential targets for UHECRs detections, and found that the proposed technique is either not viable or not competitive with traditional ground-based UHECRs detectors.
1405.5836
The morphology of galaxies with quiescent recent assembly history in Lambda-CDM universe
Pedrosa et al
Standard disc formation scenario: discs form as the gas cools and flows into the center of the DM halo, conserving the specific angular momentum. Major mergers have been shown to be able to destroy or highly perturb the disc components. More recently, the alignment of the material that is accreted to form the galaxy has been pointed out as a key ingredient to determine galaxy morphology. However, in a hierarchical scenario galaxy formation is a complex process which combiners these processes, and others, in a non-linear way so that the origin of galaxy morphology remains to be fully understood. Aim at exploring the differences in the formation histories of galaxies with a variety of morphology but quite recent merger histories to identify which mechanisms are playing a major role. Analyze when minor mergers could be considered relevant to determine galaxy morphology. Also study the specific angular momentum content of the disc and central spheroidal components, separately. Use cosmological hydrodynamical simulations that include an effective, physically-motivated SN feedback which is able to regulate the SF in hales of different masses. Analyze the morphology and formation history of a sample of 15 galaxies of a cosmological simulation. Perform a spheroid-disc decomposition of the selected galaxies and their progenitor systems. The angular momentum orientation of the merging systems as well as their relative masses are estimated to analyze the role played by orientation and by minor mergers in the determination of the morphology. Find the discs to be formed by conserving the specific angular momentum in accordance with the classical disk formation model. The specific angular momentum of the stellar central spheroid correlates with the DM halo angular momentum determining a power law.
1405.5857
A joint analysis of Planck and BICEP2 B modes including dust polarization uncertainty
Mortonson, Seljak
Analyze BICEP2 and Planck data using a model that includes CMB lensing, gravity waves, and polarized dust. Recently published Planck dust polarization maps have highlighted the difficulty of estimating the amount of dust polarization in low intensity regions, suggesting that the polarization fractions have considerable uncertainties and may be significantly higher than previous predictions. In this paper, do not assume anything about the dust polarization, except for the power spectrum shape, which is taken to be C^{BB,dust}_ell \propto ell^{-2.3}. The resulting joint BICEP2+Planck analysis favors solutions without gravity waves, and the upper limit on the tensor-to-scalar ratio is r<0.11, a slight improvement relative to the Planck analysis alone which gives r<0.13 (95% CL). The estimated amplitude of the dust polarization PS is in rough agreement with expectations for this field based on HI column density. Address the cross-correlation analysis of BICEP2 at 150 GHz with BICEP1 at 100 GHz as a test of FG contamination. Find that the null hypothesis of dust and lensing with r=0 gives Delta chi^2<2 relative to the hypothesis of no dust, so the frequency analysis does not strongly favor either model over the other. Also discuss how Planck dust polarization maps may improve constraints. If the dust polarization is measured perfectly, the limit can reach r<0.05 (or the corresponding detection significance if the observed dust signal plus the expected lensing signal is below the BICEP2 observations), but this degrades quickly to almost no improvement if the dust calibration error is 20% larger or if the Planck dust maps are not processed through the BICEP2 pipeline, including sampling variance noise.
Thursday, May 22, 2014
Day 662
Thursday.
1405.3332
First detection of $^{56}$Co gamma-ray lines from type Ia supernova (SN2014J) with INTEGRAL
Churazov et al
First ever detection of 56Co lines at 847 and 1237 keV and a continuum in the 200-400 keV band from Type Ia SN2014J in M82. Data taken between 50th and 100th day since the SN2014J outburst. The line fluxes suggest that 0.62pm0.13 Msun of radioactive 56Ni were synthesized during the explosion. Line broadening gives a characteristic eject expansion velocity V_e~2100pm500 km/s. The flux at lower energies (200-400 keV) flux is consistent with the 3-photon positronium annihilation, Compton down scattering and absorption in the ~1. Msun eject composed from equal fractions of Fe-group and intermediate-mass elements and a kinetic energy E_k~1.4e51 erg. All these parameters are in broad agreement with a "canonical" model of an explosion of a Chandrasekhar-mass White Dwarf, providing an unambiguous proof of the nature of Type Ia supernovae as a thermonuclear explosion of a solar mass compact object.
1405.5216
Dwarf galaxies in CDM and SIDM with baryons: observational probes of the nature of dark matter
Vogelsberger et al
Dark matter collisions lead to dwarf galaxies with larger stellar cores and smaller stellar central densities compared to the CDM case. The central metallicity within 1kpc is also larger by up to ~15% in the former case. Conclude that the mass distribution and characteristics of the central stars in dwarf galaxies can potentially be used to probe the self-interacting nature of DM.
1405.5221
The decomposed bulge and disk size-mass relations of massive galaxies at 1<z<3 in CANDELS
Bruce et al
A mass-selected sample of M*>1e11 Msun galaxies at 1<z<3 in CANDELS UDS and COSMOS fields, decomposed into their bulge and disk components according to their H(160)-band morphologies. Extend this analysis to multiple bands, and conduct individual bulge and disk component SED fitting with stellar-mass and star-formation rate estimates for the separate bulge and disk components. These have been combined with size measurements to explore the evolution of these massive high-z galaxies. By utilizing the new decomposed stellar-mass estimates, confirm that the bulge components display a stronger size evolution than the disks. This can be seen from both the fraction of bulge components which lie below the local relation and the median sizes of the bulge components, where the bulges are a median factor of 2.9x times smaller than similarly massive local galaxies at 1<z<2 and 3.4x smaller at 2<z<3; for the disks the corresponding factors are 1.6 and 2.0. Moreover, by splitting the sample in the the passive and SF bulge and disk sub-populations and examining their sizes as a fraction of their present-day counter-parts, find that the SF and passive bulges are equally compact, SF disks are larger, while the passive disks have intermediate sizes. This trend is not evident when classifying galaxy morphology on the basis of single-Sersic fits and adopting the overall SFRs. By evolving the SFHs of the passive disks back to the redshifts when the passive disks were last active, show that the passive and SF disks have consistent sizes at the relevant epoch. These trends need to be reproduced by any mechanisms which attempt to explain the morphological evolution of galaxies.
1405.3332
First detection of $^{56}$Co gamma-ray lines from type Ia supernova (SN2014J) with INTEGRAL
Churazov et al
First ever detection of 56Co lines at 847 and 1237 keV and a continuum in the 200-400 keV band from Type Ia SN2014J in M82. Data taken between 50th and 100th day since the SN2014J outburst. The line fluxes suggest that 0.62pm0.13 Msun of radioactive 56Ni were synthesized during the explosion. Line broadening gives a characteristic eject expansion velocity V_e~2100pm500 km/s. The flux at lower energies (200-400 keV) flux is consistent with the 3-photon positronium annihilation, Compton down scattering and absorption in the ~1. Msun eject composed from equal fractions of Fe-group and intermediate-mass elements and a kinetic energy E_k~1.4e51 erg. All these parameters are in broad agreement with a "canonical" model of an explosion of a Chandrasekhar-mass White Dwarf, providing an unambiguous proof of the nature of Type Ia supernovae as a thermonuclear explosion of a solar mass compact object.
1405.5216
Dwarf galaxies in CDM and SIDM with baryons: observational probes of the nature of dark matter
Vogelsberger et al
Dark matter collisions lead to dwarf galaxies with larger stellar cores and smaller stellar central densities compared to the CDM case. The central metallicity within 1kpc is also larger by up to ~15% in the former case. Conclude that the mass distribution and characteristics of the central stars in dwarf galaxies can potentially be used to probe the self-interacting nature of DM.
1405.5221
The decomposed bulge and disk size-mass relations of massive galaxies at 1<z<3 in CANDELS
Bruce et al
A mass-selected sample of M*>1e11 Msun galaxies at 1<z<3 in CANDELS UDS and COSMOS fields, decomposed into their bulge and disk components according to their H(160)-band morphologies. Extend this analysis to multiple bands, and conduct individual bulge and disk component SED fitting with stellar-mass and star-formation rate estimates for the separate bulge and disk components. These have been combined with size measurements to explore the evolution of these massive high-z galaxies. By utilizing the new decomposed stellar-mass estimates, confirm that the bulge components display a stronger size evolution than the disks. This can be seen from both the fraction of bulge components which lie below the local relation and the median sizes of the bulge components, where the bulges are a median factor of 2.9x times smaller than similarly massive local galaxies at 1<z<2 and 3.4x smaller at 2<z<3; for the disks the corresponding factors are 1.6 and 2.0. Moreover, by splitting the sample in the the passive and SF bulge and disk sub-populations and examining their sizes as a fraction of their present-day counter-parts, find that the SF and passive bulges are equally compact, SF disks are larger, while the passive disks have intermediate sizes. This trend is not evident when classifying galaxy morphology on the basis of single-Sersic fits and adopting the overall SFRs. By evolving the SFHs of the passive disks back to the redshifts when the passive disks were last active, show that the passive and SF disks have consistent sizes at the relevant epoch. These trends need to be reproduced by any mechanisms which attempt to explain the morphological evolution of galaxies.
Wednesday, May 21, 2014
Day 661
Wednesday.
1405.4855
Halo bias in mixed dark matter cosmologies
LoVerde
In a universe with multiple types of matter fluctuations (e.g., with massive neutrinos), the relation between the halo field and the matter fluctuations may be more complicated than "CDM haloes trace the LSS of matter". Develop a method for calculating the bias factor relating fluctuations n the halo number density to fluctuations in the mass density in the presence of multiple fluctuation components of the energy density. In the presence of massive neutrinos, find a small but pronounced features in the halo bias near the neutrino free streaming scale. The neutrino feature is a small step with amplitude that increases with halo mass and neutrino mass density. The scale-dependent halo bias lessens the suppression of the small-scale halo power spectrum and should therefore weaken constraints on neutrino mass from the galaxy auto-power spectrum and correlation function. On the other hand, the feature in the bias is itself a novel signature of massive neutrinos that can be studied independently.
1405.4856
Cookie-cutter haloes: the remarkable constancy of the stellar mass function of satellite galaxies at 0.2<z<1.2
Tal et al
Observational study of the stellar MF of satellite galaxies around central galaxies at 0.2<z<1.2. 4 bins of central galaxy mass in 3 redshift bins. Results show that the stellar MF of satellite galaxies increases with central galaxy mass, and that the distribution of satellite masses at fixed central mass is at most weakly dependent on redshift. Conclude that the average mass distribution of galaxies in groups is remarkably universal even out to z=1.2 and that it can be uniquely characterized by the group central galaxy mass. This further suggests that as central galaxies grow in stellar mass, they do so in tandem with the mass growth of their satellites. Finally, we classify all galaxies as either star forming or quiescent, and derive the mass functions of each subpopulation separately. Find that the mass distribution of both star forming and quiescent satellites show minimal redshift dependence at fixed central mass. However, while the fraction of quiescent satellite galaxies increases rapidly with increasing central galaxy mass, that of star forming satellites decreases.
1405.4858
Spherical collapse in $\nu \Lambda CDM$
LoVerde
The abundance of massive DM haloes hosting galaxy clusters provide an important test of the masses of relic neutrino species. The dominant effect of neutrino mass is to lower the typical amplitude of density perturbations that eventually form haloes, but for neutrino masses >0.4eV the threshold for halo formation can be changed significantly as well. Study the spherical collapse model for halo formation in cosmologies with neutrino masses in the range M_nu,i = 0.05eV-1eV and find that halo formation is differently sensitive to Omega_nu and m_nu. That is, different neutrino hierarchies with common Omega_nu are in principle distinguishable. The added sensitivity to m_nu is small but potentially important for scenarios with heavier sterile neutrinos. Massive neutrinos cause the evolution of density perturbations to be scale-dependent at high redshift which complicates the usual mapping between the collapse threshold and halo abundance. Propose one way of handling this and compute the correction to the halo mass function within this framework. For Sum m_nu,i<0.3eV, prescription for the halo abundance is only ~<15% different than the standard calculation. However for larger neutrino masses the differences approach 50-100% which, if verified by simulations, could alter neutrino mass constraints from cluster abundance.
1405.5014
Microlensing of the broad-line region in the quadruply imaged quasar HE0435-1223
Braibant, Hutsemékers, Sluse, Anguita, GarcÃa-Vergara
Using IR spectra of the z=1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO VLT, detected a clear microlensing effect in images A and D. While microlensing affects the blue and red wings of the Halpha line profile in image D very differently, it de-magnifies the line core in image A. The combination of these different effects sets constrains on the line-emitting region; these constraints suggest that a rotating ring is at the origin of the Halpha line. Visible spectra obtained in 2004 and 2012 indicate that the MgII line profile is micro lensed in the same way as the Halpha line. Results therefore favor flattened geometries for the low-ionization line-emitting region, for example, a Keplerian disk. Biconical models cannot be ruled out but require more fine-tuning. Flux ratios between the different images are also derived and confirm flux anomalies with respect to estimates from lens models with smooth mass distributions.
1405.4855
Halo bias in mixed dark matter cosmologies
LoVerde
In a universe with multiple types of matter fluctuations (e.g., with massive neutrinos), the relation between the halo field and the matter fluctuations may be more complicated than "CDM haloes trace the LSS of matter". Develop a method for calculating the bias factor relating fluctuations n the halo number density to fluctuations in the mass density in the presence of multiple fluctuation components of the energy density. In the presence of massive neutrinos, find a small but pronounced features in the halo bias near the neutrino free streaming scale. The neutrino feature is a small step with amplitude that increases with halo mass and neutrino mass density. The scale-dependent halo bias lessens the suppression of the small-scale halo power spectrum and should therefore weaken constraints on neutrino mass from the galaxy auto-power spectrum and correlation function. On the other hand, the feature in the bias is itself a novel signature of massive neutrinos that can be studied independently.
1405.4856
Cookie-cutter haloes: the remarkable constancy of the stellar mass function of satellite galaxies at 0.2<z<1.2
Tal et al
Observational study of the stellar MF of satellite galaxies around central galaxies at 0.2<z<1.2. 4 bins of central galaxy mass in 3 redshift bins. Results show that the stellar MF of satellite galaxies increases with central galaxy mass, and that the distribution of satellite masses at fixed central mass is at most weakly dependent on redshift. Conclude that the average mass distribution of galaxies in groups is remarkably universal even out to z=1.2 and that it can be uniquely characterized by the group central galaxy mass. This further suggests that as central galaxies grow in stellar mass, they do so in tandem with the mass growth of their satellites. Finally, we classify all galaxies as either star forming or quiescent, and derive the mass functions of each subpopulation separately. Find that the mass distribution of both star forming and quiescent satellites show minimal redshift dependence at fixed central mass. However, while the fraction of quiescent satellite galaxies increases rapidly with increasing central galaxy mass, that of star forming satellites decreases.
1405.4858
Spherical collapse in $\nu \Lambda CDM$
LoVerde
The abundance of massive DM haloes hosting galaxy clusters provide an important test of the masses of relic neutrino species. The dominant effect of neutrino mass is to lower the typical amplitude of density perturbations that eventually form haloes, but for neutrino masses >0.4eV the threshold for halo formation can be changed significantly as well. Study the spherical collapse model for halo formation in cosmologies with neutrino masses in the range M_nu,i = 0.05eV-1eV and find that halo formation is differently sensitive to Omega_nu and m_nu. That is, different neutrino hierarchies with common Omega_nu are in principle distinguishable. The added sensitivity to m_nu is small but potentially important for scenarios with heavier sterile neutrinos. Massive neutrinos cause the evolution of density perturbations to be scale-dependent at high redshift which complicates the usual mapping between the collapse threshold and halo abundance. Propose one way of handling this and compute the correction to the halo mass function within this framework. For Sum m_nu,i<0.3eV, prescription for the halo abundance is only ~<15% different than the standard calculation. However for larger neutrino masses the differences approach 50-100% which, if verified by simulations, could alter neutrino mass constraints from cluster abundance.
1405.5014
Microlensing of the broad-line region in the quadruply imaged quasar HE0435-1223
Braibant, Hutsemékers, Sluse, Anguita, GarcÃa-Vergara
Using IR spectra of the z=1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO VLT, detected a clear microlensing effect in images A and D. While microlensing affects the blue and red wings of the Halpha line profile in image D very differently, it de-magnifies the line core in image A. The combination of these different effects sets constrains on the line-emitting region; these constraints suggest that a rotating ring is at the origin of the Halpha line. Visible spectra obtained in 2004 and 2012 indicate that the MgII line profile is micro lensed in the same way as the Halpha line. Results therefore favor flattened geometries for the low-ionization line-emitting region, for example, a Keplerian disk. Biconical models cannot be ruled out but require more fine-tuning. Flux ratios between the different images are also derived and confirm flux anomalies with respect to estimates from lens models with smooth mass distributions.
Tuesday, May 20, 2014
Day 660
Tuesday.
1405.3985
Running with BICEP2: implications for small-scale problems in CDM
Garrison-Kimmel, Horiuchi, Abazajian, Bullock, Kaplinghat
The BICEP2 results suggest a roll-off in power towards small scales in the primordial matter power spectrum. Among the simplest possibilities is a running of the spectral index. Show that the preferred level of running alleviates small-scale issues within the LCDM model, more so even than viable WDM models. Use cosmological zoom-in simulations of fMW-size halo along with full-box simulations to compare predictions among four separate cosmologies: a BICEP2-inspired running indue model (alpha_s=-0.024), two fixed-tilt LCDM models motivated by Planck, and a 2.6 keV thermal WDM model. Find that the running BICEP2 model reduces the central densities of large dwarf-size haloes (Vmax~30-80 km/s) and alleviates the too-big-to-fail problem significantly compared to the adopted Planck and WDM cases. Further, the BICEP2 model suppresses the count of small sub haloes by ~50% relative to Planck models, and yields a significantly lower "boost" factor for DM annihilation signals. Findings highlight the need to understand the shape of the primordial PS in order to correctly interpret small-scale data.
1405.4318
Baryonic and dark matter distribution in cosmological simulations of spiral galaxies
Mollitor, Nezri, Teyssier
High-res cosmo hydrosim of MW-sized haloes; consistently tuned SFR and SNe feedback. Obtain an extended disk and a flat rotation curve in one of the simulated galaxies; DM density in the solar neighborhood in agreement with observations [what are the observational constraint of DM in the Solar neighborhood?]. DM distribution show the interaction with the baryons and how the DM is first contracted by SF and then cored by feedback processes. Analysing the clump spectrum, find a shift in mass with regard to corresponding DM-only sims and obtain a distribution of luminous satellites comparable with MW spheroidal dwarf galaxies.
1405.4523
Abundance of field galaxies
Klypin et al
Present new measurements of the abundance of galaxies with a given circular velocity of the Local Volume: a region centered on the MW and extending to distance 10 Mpc. The sample of 750 mostly dwarf galaxies provides a unique opportunity to study the abundance and properties of galaxies down to absolute magnitudes MB=-10, and virial masses 1e9 Msun. Find that the standard LCDM model gives remarkable accurate estimates for the velocity function of galaxies with circular velocities V>60 km/s and corresponding virial masses Mvir>3e10 Msun, but it badly fails by over-predicting 5x the abundance of large dwarfs with velocities V=30-50 km/s. The WDM models cannot explain the data either, regardless of mass of the WDM particle. Just as in previous observational studies, find a shallow asymptotic slope dN/dlogV=V^alpha, alpha=-1 of the velocity function, which is inconsistent with the standard LCDM model that predicts the slope alpha=-3. Though reminiscent of the known overabundance of satellites problem, the overabundance of field galaxies is a much more difficult problem. For the LCDM model to survive, in the 10 Mpc radius of the MW there should be 1000 dark galaxies with virial mass Mvir=1e10 Msun, extremely low surface brightness and no detectable HI gas. So far none of this type of galaxies have been discovered.
1405.3985
Running with BICEP2: implications for small-scale problems in CDM
Garrison-Kimmel, Horiuchi, Abazajian, Bullock, Kaplinghat
The BICEP2 results suggest a roll-off in power towards small scales in the primordial matter power spectrum. Among the simplest possibilities is a running of the spectral index. Show that the preferred level of running alleviates small-scale issues within the LCDM model, more so even than viable WDM models. Use cosmological zoom-in simulations of fMW-size halo along with full-box simulations to compare predictions among four separate cosmologies: a BICEP2-inspired running indue model (alpha_s=-0.024), two fixed-tilt LCDM models motivated by Planck, and a 2.6 keV thermal WDM model. Find that the running BICEP2 model reduces the central densities of large dwarf-size haloes (Vmax~30-80 km/s) and alleviates the too-big-to-fail problem significantly compared to the adopted Planck and WDM cases. Further, the BICEP2 model suppresses the count of small sub haloes by ~50% relative to Planck models, and yields a significantly lower "boost" factor for DM annihilation signals. Findings highlight the need to understand the shape of the primordial PS in order to correctly interpret small-scale data.
1405.4318
Baryonic and dark matter distribution in cosmological simulations of spiral galaxies
Mollitor, Nezri, Teyssier
High-res cosmo hydrosim of MW-sized haloes; consistently tuned SFR and SNe feedback. Obtain an extended disk and a flat rotation curve in one of the simulated galaxies; DM density in the solar neighborhood in agreement with observations [what are the observational constraint of DM in the Solar neighborhood?]. DM distribution show the interaction with the baryons and how the DM is first contracted by SF and then cored by feedback processes. Analysing the clump spectrum, find a shift in mass with regard to corresponding DM-only sims and obtain a distribution of luminous satellites comparable with MW spheroidal dwarf galaxies.
1405.4523
Abundance of field galaxies
Klypin et al
Present new measurements of the abundance of galaxies with a given circular velocity of the Local Volume: a region centered on the MW and extending to distance 10 Mpc. The sample of 750 mostly dwarf galaxies provides a unique opportunity to study the abundance and properties of galaxies down to absolute magnitudes MB=-10, and virial masses 1e9 Msun. Find that the standard LCDM model gives remarkable accurate estimates for the velocity function of galaxies with circular velocities V>60 km/s and corresponding virial masses Mvir>3e10 Msun, but it badly fails by over-predicting 5x the abundance of large dwarfs with velocities V=30-50 km/s. The WDM models cannot explain the data either, regardless of mass of the WDM particle. Just as in previous observational studies, find a shallow asymptotic slope dN/dlogV=V^alpha, alpha=-1 of the velocity function, which is inconsistent with the standard LCDM model that predicts the slope alpha=-3. Though reminiscent of the known overabundance of satellites problem, the overabundance of field galaxies is a much more difficult problem. For the LCDM model to survive, in the 10 Mpc radius of the MW there should be 1000 dark galaxies with virial mass Mvir=1e10 Msun, extremely low surface brightness and no detectable HI gas. So far none of this type of galaxies have been discovered.
Monday, May 19, 2014
Day 659
Monday.
1405.3984
Revisiting the universality of (multiple) star formation in present-day star formation regions
Marks, Leigh, Giersz, Pfalzner, Pflamm-Altenburg, Oh
Dynamical interactions in clustered regions change star populations; but stellar density-dependent modification of a universal initial binary population (efficiency of binary disruption is thought to be determined by stellar density) cannot explain the observations. Re-analyze data with different model assumptions: (1) non-universality without dynamical modification and (2) universality with dynamics. Illustrate that the standard model does account for all known populations if regions were significantly denser in the past. Some of the effects of using present-day cluster properties as proxies for their past values are emphasized and that the degeneracy between age and density of a SF region can not be omitted when interpreting multiplicity data. A new analysis of the Corona Australis sregion is performed within the standard model. It is found that this region is likely as involved as Taurus and an initial density of ~190 Msun/pc^3 is required to produce the presently observed binary population, which is close to its present-day density.
1405.4285
Mass and galaxy distributions of four massive galaxy clusters from Dark Energy Survey Science Verification data
Melchior ... Huff, Rykoff, Gruen, Armstrong, Bacon, Bernstein, Bridle, Jain, Krause, ... et al
Measure the WL masses and galaxy distributions of four massive galaxy clusters observed during the Science Verification phase of the DES with the purpose of 1) validating the DECam imager for the task of measuring WL shapes, and 2) utilizing DECam's large FoV to map out the clusters and their environments over 90 arcmin. Conduct a series of rigorous tests on astrometry, photometry, image quality, PSF modeling, and shear measurement accuracy to single out flaws in the data and also to identify the optical data processing steps and parameters. Find Science Verification data from DECam to be suitable for lensing analyses. The PSF is generally well-behaved, but the modeling is rendered difficult by a flux-dependent PSF width. Employ photometric redshifts to distinguish between FG and BG galaxies, and a red-sequence cluster finder to provide cluster richness estimates and cluster-galaxy distributions. By fitting NFW profiles to the clusters in this study, determine WL masses that are in agreement with previous work. For Abell 3261, provide the first estimates of redshift, WL mass, and richness. In addition, the cluster-galaxy distributions indicate the existence of filaments attached to 1E 0657-56 and RXC J2248.7-4431, stretching out as far as 1 degree (approximately 20 Mpc), showcasing the potential of DECam and DES for detailed studies of degree-scale features on the sky.
1405.3984
Revisiting the universality of (multiple) star formation in present-day star formation regions
Marks, Leigh, Giersz, Pfalzner, Pflamm-Altenburg, Oh
Dynamical interactions in clustered regions change star populations; but stellar density-dependent modification of a universal initial binary population (efficiency of binary disruption is thought to be determined by stellar density) cannot explain the observations. Re-analyze data with different model assumptions: (1) non-universality without dynamical modification and (2) universality with dynamics. Illustrate that the standard model does account for all known populations if regions were significantly denser in the past. Some of the effects of using present-day cluster properties as proxies for their past values are emphasized and that the degeneracy between age and density of a SF region can not be omitted when interpreting multiplicity data. A new analysis of the Corona Australis sregion is performed within the standard model. It is found that this region is likely as involved as Taurus and an initial density of ~190 Msun/pc^3 is required to produce the presently observed binary population, which is close to its present-day density.
1405.4285
Mass and galaxy distributions of four massive galaxy clusters from Dark Energy Survey Science Verification data
Melchior ... Huff, Rykoff, Gruen, Armstrong, Bacon, Bernstein, Bridle, Jain, Krause, ... et al
Measure the WL masses and galaxy distributions of four massive galaxy clusters observed during the Science Verification phase of the DES with the purpose of 1) validating the DECam imager for the task of measuring WL shapes, and 2) utilizing DECam's large FoV to map out the clusters and their environments over 90 arcmin. Conduct a series of rigorous tests on astrometry, photometry, image quality, PSF modeling, and shear measurement accuracy to single out flaws in the data and also to identify the optical data processing steps and parameters. Find Science Verification data from DECam to be suitable for lensing analyses. The PSF is generally well-behaved, but the modeling is rendered difficult by a flux-dependent PSF width. Employ photometric redshifts to distinguish between FG and BG galaxies, and a red-sequence cluster finder to provide cluster richness estimates and cluster-galaxy distributions. By fitting NFW profiles to the clusters in this study, determine WL masses that are in agreement with previous work. For Abell 3261, provide the first estimates of redshift, WL mass, and richness. In addition, the cluster-galaxy distributions indicate the existence of filaments attached to 1E 0657-56 and RXC J2248.7-4431, stretching out as far as 1 degree (approximately 20 Mpc), showcasing the potential of DECam and DES for detailed studies of degree-scale features on the sky.
Friday, May 16, 2014
Day 658
Friday.
1405.3660
3-dimensional spherical analyses of cosmological spectroscopic surveys
Nicola, Refregier, Amara, Paranjape
Compare spherical harmonic tomography (SHT) power spectrum C^{ij}_ell and the spherical Fourier Bessel (SFB) power spectrm C_ell(k,k'). Show that overlapping redshift bins may improve cosmological constraints using the SHT statistics when then number of bins is small, and that the SFB constraints are quite robust to changes in the assumed redshift-distance relation. Also find that the SHT can be tailored to be more sensitive to modes at redshifts close to the survey boundary and may yield somewhat tighter constraints. In this context, discuss the pros and cons of the different techniques and their impact on the design and analysis of future wide field spectroscopic surveys.
1405.3661
Discovery of a strong lensing galaxy embedded in a cluster at z=1.62
Wong et al
The highest redshift strong lens known to date; the source is at z=2.26.
1405.3749
The Illustris Simulation: the evolution of galaxy populations across cosmic time
Genel, Vogelsberger, Springel, … Hernquist, et al
Present an overview of galaxy evolution across cosmic time in the Illustris Simulation. (106.5 Mpc)^3 box, 2*1820^3 particles, down to z=0 using REPO moving-mesh code. Reproduces galaxy populations across various redshifts. Discuss (a) the buildup of galactic mass, showing stellar MFs and the relations between stellar mass and halo mass from z=7 to 0, (b) galaxy number density profiles around massive central galaxies out to z=4, (c) the gas and total baryon content of both galaxies and their haloes for different z, and as a function of mass and radius, and (d) the evolution of galaxy specific star-formation rates up to z=8. In addition, (i) present a qualitative analysis of galaxy morphologies from z=5 to 0, for the stellar as well as the gaseous components, and their appearance in HST mock observations, (ii) follow galaxies selected at z=2 to their z=0 descendants, and quantify their growth and merger histories, and (iii) track massive z=0 galaxies to high z and study their joint evolution in SF activity and compactness. Conclude with a discussion of several disagreements with observations, and lay out a possible directions for future research.
1405.3660
3-dimensional spherical analyses of cosmological spectroscopic surveys
Nicola, Refregier, Amara, Paranjape
Compare spherical harmonic tomography (SHT) power spectrum C^{ij}_ell and the spherical Fourier Bessel (SFB) power spectrm C_ell(k,k'). Show that overlapping redshift bins may improve cosmological constraints using the SHT statistics when then number of bins is small, and that the SFB constraints are quite robust to changes in the assumed redshift-distance relation. Also find that the SHT can be tailored to be more sensitive to modes at redshifts close to the survey boundary and may yield somewhat tighter constraints. In this context, discuss the pros and cons of the different techniques and their impact on the design and analysis of future wide field spectroscopic surveys.
1405.3661
Discovery of a strong lensing galaxy embedded in a cluster at z=1.62
Wong et al
The highest redshift strong lens known to date; the source is at z=2.26.
1405.3749
The Illustris Simulation: the evolution of galaxy populations across cosmic time
Genel, Vogelsberger, Springel, … Hernquist, et al
Present an overview of galaxy evolution across cosmic time in the Illustris Simulation. (106.5 Mpc)^3 box, 2*1820^3 particles, down to z=0 using REPO moving-mesh code. Reproduces galaxy populations across various redshifts. Discuss (a) the buildup of galactic mass, showing stellar MFs and the relations between stellar mass and halo mass from z=7 to 0, (b) galaxy number density profiles around massive central galaxies out to z=4, (c) the gas and total baryon content of both galaxies and their haloes for different z, and as a function of mass and radius, and (d) the evolution of galaxy specific star-formation rates up to z=8. In addition, (i) present a qualitative analysis of galaxy morphologies from z=5 to 0, for the stellar as well as the gaseous components, and their appearance in HST mock observations, (ii) follow galaxies selected at z=2 to their z=0 descendants, and quantify their growth and merger histories, and (iii) track massive z=0 galaxies to high z and study their joint evolution in SF activity and compactness. Conclude with a discussion of several disagreements with observations, and lay out a possible directions for future research.
Thursday, May 15, 2014
Day 657
Thursday.
1405.2954
On the benefits of promoting diversity of ideas
Loeb
10 examples where astronomers believed that they knew the truth when data was scarce, leading to wrong strategic decisions in research plans, causing unnecessary delays in finding the truth. Advocate affirmative action for diversity of ideas by telescope-time allocation committees and funding agencies.
1405.3303
Mass and magnification maps for the Hubble Space Telescope Frontier Fields clusters: implications for high redshift studies
Richard, … Limousin, Jullo, … Ebeling, Kneib, Natarajan, Egami, … Bower, et al
HFF is the largest HST program to probe the distant Universe by massive galaxy cluster lensing. Present models of the mass distribution in 6 of the HFF cluster lenses, derived from a joint SL and WL analysis anchored by 618 multiple-image systems identified in existing HST data. The resulting maps of the projected has distribution and of the gravitational magnification effectively calibrate the HFF clusters as gravitational telescopes. Allowing the computation of search areas in the source plane, these maps are provided to the community to facilitate the exploitation of forthcoming HFF data for quantitative studies of the gravitationally lensed population of background galaxies. Models of the gravitational magnification afforded by the HFF clusters allow quantification of the lensing-induced boost in sensitivity over blank-filed observations and predict that galaxies at z>10 and as faint as m(AB)=32 will be detectable, up to 2 mags fainter than the limit of HUDF.
1405.3440
Ultra-faint high-redshift galaxies in the Frontier Fields
Yue et al
In FF, galaxies as faint as m~33-34 AB mag at 1.6um can be detected. Such faint galaxies are hosted by DM halos of mass ~1e9 Msun and dominate the ionizing photon budget over currently observed bright galaxies, thus allowing for the first time the investigation of the dominant reionization sources. In addition, the observed number of these galaxies can be used to constrain the role of feedback in suppressing SF in small haloes: for example, if galaxy formation is suppressed in haloes with circular velocity v_c<50 km/s, galaxies fainter than m=31 should not be detected in the FFs.
1405.3582
Hubble Frontier Fields : High precision strong lensing analysis of the cluster MACSJ0416.1-2403 using ~200 multiple images
Jauzac et al
From 3-band HST/ACS observations, discover 51 new multiply-imaged systems for a total of 68 systems and 194 images. They provide critical additional constraints that helps derive the mass distribution in the cluster core below the percent level. In comparison, the earlier published mass model used the CLASH survey data with only 23 multiple systems. Using LENSTOOL, build a high precision mass model that comprises of 2 cluster-scale DM haloes and 98 galaxy-scale haloes to describe the mass distribution of MACSJ0416. Concentrating on the subset of 57 multiply imaged systems used in the optimization, the best-fit mass model has an average error on the predicted image positions of rms=0.68", almost a factor of 2 improvement compared to the rms=1.17" obtained with the pre-HFF mass model (which used only 17 multiply imaged systems). THe total mass within an aperture of 200 kpc is found to be M=1.60pm0.01e14 Msun. Finally, quantify the gain in precision on the magnification of high-z galaxies, and find an improvement by a factor of ~2.5x in the statistical error. With the new HFF, entering the domain of high-precision mass measurement for massive galaxy clusters.
1405.2954
On the benefits of promoting diversity of ideas
Loeb
10 examples where astronomers believed that they knew the truth when data was scarce, leading to wrong strategic decisions in research plans, causing unnecessary delays in finding the truth. Advocate affirmative action for diversity of ideas by telescope-time allocation committees and funding agencies.
1405.3303
Mass and magnification maps for the Hubble Space Telescope Frontier Fields clusters: implications for high redshift studies
Richard, … Limousin, Jullo, … Ebeling, Kneib, Natarajan, Egami, … Bower, et al
HFF is the largest HST program to probe the distant Universe by massive galaxy cluster lensing. Present models of the mass distribution in 6 of the HFF cluster lenses, derived from a joint SL and WL analysis anchored by 618 multiple-image systems identified in existing HST data. The resulting maps of the projected has distribution and of the gravitational magnification effectively calibrate the HFF clusters as gravitational telescopes. Allowing the computation of search areas in the source plane, these maps are provided to the community to facilitate the exploitation of forthcoming HFF data for quantitative studies of the gravitationally lensed population of background galaxies. Models of the gravitational magnification afforded by the HFF clusters allow quantification of the lensing-induced boost in sensitivity over blank-filed observations and predict that galaxies at z>10 and as faint as m(AB)=32 will be detectable, up to 2 mags fainter than the limit of HUDF.
1405.3440
Ultra-faint high-redshift galaxies in the Frontier Fields
Yue et al
In FF, galaxies as faint as m~33-34 AB mag at 1.6um can be detected. Such faint galaxies are hosted by DM halos of mass ~1e9 Msun and dominate the ionizing photon budget over currently observed bright galaxies, thus allowing for the first time the investigation of the dominant reionization sources. In addition, the observed number of these galaxies can be used to constrain the role of feedback in suppressing SF in small haloes: for example, if galaxy formation is suppressed in haloes with circular velocity v_c<50 km/s, galaxies fainter than m=31 should not be detected in the FFs.
1405.3582
Hubble Frontier Fields : High precision strong lensing analysis of the cluster MACSJ0416.1-2403 using ~200 multiple images
Jauzac et al
From 3-band HST/ACS observations, discover 51 new multiply-imaged systems for a total of 68 systems and 194 images. They provide critical additional constraints that helps derive the mass distribution in the cluster core below the percent level. In comparison, the earlier published mass model used the CLASH survey data with only 23 multiple systems. Using LENSTOOL, build a high precision mass model that comprises of 2 cluster-scale DM haloes and 98 galaxy-scale haloes to describe the mass distribution of MACSJ0416. Concentrating on the subset of 57 multiply imaged systems used in the optimization, the best-fit mass model has an average error on the predicted image positions of rms=0.68", almost a factor of 2 improvement compared to the rms=1.17" obtained with the pre-HFF mass model (which used only 17 multiply imaged systems). THe total mass within an aperture of 200 kpc is found to be M=1.60pm0.01e14 Msun. Finally, quantify the gain in precision on the magnification of high-z galaxies, and find an improvement by a factor of ~2.5x in the statistical error. With the new HFF, entering the domain of high-precision mass measurement for massive galaxy clusters.
Day 656
Wednesday.
1405.2921
Introducing the Illustris project: simulating the coevolution of dark and visible matter in the Universe
Vogelsberger, Genel, Springel, Torrey, Sijacki, Xu, Snyder, Nelson, Hernquist
Illustris Project: a series of large-scale hydro-sim of galaxy formation. Highest resolution: (100Mpc)^3, DM resolution 6.3e6Msun, and initial baryonic matter mass resolution of 1.3e6Msun. At z=0, softening scales of 710 pc, and the smallest hydro gas cells have extent of 48 pc. Follow dynamical evolution of 2x1820^3 resolution elements and in addition passively evolve 1820^3 MC tracer particles reaching a total particle count of 18 billion. The galaxy formation model includes primordial and metal-line cooling with self-shielding corrections, stellar evolution, stellar feedback, gas recycling, chemical enrichment, SMBH growth, and feedback from AGN. At z=0 the simulation volume contains about 40k well-resolved galaxies covering a diverse range of morphologies and colors including early-type, late-type and irregular galaxies. The simulation reproduces the cosmic SFR density, the galaxy luminosity function, and baryon conversion efficiency at z=0. It also qualitatively captures the impact of galaxy environment on the red fractions of galaxies. The internal velocity structure of selected well-resolved disk galaxies obeys the stellar and baryonic TF relation together with flat circular velocity curves. In the well-resolved regime the simulation reproduces the observed mix of early-type and late-type galaxies. Model predicts a halo mass dependent impact of baryonic effects on the halo MF and the masses of haloes caused by feedback form SN and AGN.
1405.2923
Orientation bias of optically selected galaxy clusters and its impact on stacked weak lensing analyses
Dietrich, et al
WL measurements of averaged shear profiles of galaxy clusters binned by some proxy for cluster mass are commonly converted to cluster mass estimates under the assumption that these cluster stacks have spherical symmetry. Test whether this assumption holds for optically selected clusters binned by estimated optical richness. Using mock catalogues from N-body sims populated with galaxies, ran a quite of optical cluster finders and estimated their optical richness. Binned galaxy clusters by true cluster mass and estimated optical richness and measure the ellitpicity of these stacks. Find that the processes of optical cluster selection and richness estimation are biased, leading to stacked structures that are elongated along the LoS. Show that WL alone cannot measure the size of this orientation bias. WL masses of stacked optically selected clusters are overestimated by 3-6% when clusters can be uniquely associated with haloes. This effect is large enough to lead to significant biases in the cosmological parameters derived from large surveys like the DES, if not calibrated via simulations or fitted simultaneously. This bias probably also contributes to the observed discrepancy between the observed and predicted SZ signal of optically-selected clusters.
1405.2921
Introducing the Illustris project: simulating the coevolution of dark and visible matter in the Universe
Vogelsberger, Genel, Springel, Torrey, Sijacki, Xu, Snyder, Nelson, Hernquist
Illustris Project: a series of large-scale hydro-sim of galaxy formation. Highest resolution: (100Mpc)^3, DM resolution 6.3e6Msun, and initial baryonic matter mass resolution of 1.3e6Msun. At z=0, softening scales of 710 pc, and the smallest hydro gas cells have extent of 48 pc. Follow dynamical evolution of 2x1820^3 resolution elements and in addition passively evolve 1820^3 MC tracer particles reaching a total particle count of 18 billion. The galaxy formation model includes primordial and metal-line cooling with self-shielding corrections, stellar evolution, stellar feedback, gas recycling, chemical enrichment, SMBH growth, and feedback from AGN. At z=0 the simulation volume contains about 40k well-resolved galaxies covering a diverse range of morphologies and colors including early-type, late-type and irregular galaxies. The simulation reproduces the cosmic SFR density, the galaxy luminosity function, and baryon conversion efficiency at z=0. It also qualitatively captures the impact of galaxy environment on the red fractions of galaxies. The internal velocity structure of selected well-resolved disk galaxies obeys the stellar and baryonic TF relation together with flat circular velocity curves. In the well-resolved regime the simulation reproduces the observed mix of early-type and late-type galaxies. Model predicts a halo mass dependent impact of baryonic effects on the halo MF and the masses of haloes caused by feedback form SN and AGN.
1405.2923
Orientation bias of optically selected galaxy clusters and its impact on stacked weak lensing analyses
Dietrich, et al
WL measurements of averaged shear profiles of galaxy clusters binned by some proxy for cluster mass are commonly converted to cluster mass estimates under the assumption that these cluster stacks have spherical symmetry. Test whether this assumption holds for optically selected clusters binned by estimated optical richness. Using mock catalogues from N-body sims populated with galaxies, ran a quite of optical cluster finders and estimated their optical richness. Binned galaxy clusters by true cluster mass and estimated optical richness and measure the ellitpicity of these stacks. Find that the processes of optical cluster selection and richness estimation are biased, leading to stacked structures that are elongated along the LoS. Show that WL alone cannot measure the size of this orientation bias. WL masses of stacked optically selected clusters are overestimated by 3-6% when clusters can be uniquely associated with haloes. This effect is large enough to lead to significant biases in the cosmological parameters derived from large surveys like the DES, if not calibrated via simulations or fitted simultaneously. This bias probably also contributes to the observed discrepancy between the observed and predicted SZ signal of optically-selected clusters.
Monday, May 12, 2014
Day 655
Tuesday.
Nature
The different neighbors around Type-1 and Type-2 active galactic nuclei
Villaroel, Korn; Gaskell
Find strong differences in the color and AGN activity of the neighbors to type-1 and type-2 AGN, and in how the fraction of AGN residing in spiral hosts changes depending n the presence or not of a neighbor. These finding suggest that an evolutionary link between the two major AGN types might exist.
1405.2338
The SLUGGS survey: exploring the metallicity gradients of nearby early-type galaxies to large radii
Pastorello et al
Stellar metallicity gradients in the outer regions of galaxies are a critical tool for disentangling the contributions of in-situ and ex-situ formed stars. In the two-phase galaxy formation scenario, the initial gas collapse creates steep metallicity gradients, while the accretion of stars formed in satellites tends to flatten these gradients in the outskirts, particularly for massive galaxies. Obtain radial stellar metallicity profiles for 22 nearby early-type galaxies. From the Ca triplet lines in the NIR, measure the metallicity of the starlight up to 3 effective radii. Find a relation between the outer metallicity gradient and galaxy mass, in the sense that lower mass systems show steeper metallicity gradients than more massive galaxies. This result is consistent with a picture in which the ratio of ex-situ to in-situ formed stars is lower in less massive galaxies as a consequence of the smaller contribution by accretion. In addition, infer a correlation between the strength of the Ca triplet feature in the NIR and the stellar IMF slope that is consistent with recent models in the literature.
1405.2340
Is the effect of the sun's gravitational potential on dark matter particles observable?
Bozorgnia, Schwetz
Gravitational focusing (GF) is negligible for low masses; in the region of DM masses below 40 GeV an annual modulation signal can be established with a future direct detection experiment. Hard to establish the presence of GF from data. In the high-mass region where GF is more important the significance of annual modulation itself is very low.
1405.2577
Dark matter heating and early core formation in dwarf galaxies
Madau, Shen, Governato
Results from LCDM sims of a group of isolated dwarf galaxies that has been shown to reproduce the observed stellar mass and cold gas content, resolved SFHs, and metallicities of dwarfs in the Local Volume. Investigate the energetics and timetable of the cusp-core transformation. SNe-driven gas outflows remove DM cusps and create kpc-size cores in all systems having a stellar mass above 1e6 Msun. The "DM core mass removal efficiency" -- dark mass ejected per unit stellar mass -- ranges today from a few to a dozen, and increases with decreasing host mass. Because dwarfs form the bulk of their stars prior to z~1 and the amount of work required for DM heating and core formation scales approximately as Mvir^5/3, the unbinding of the DM cusp starts early and the formation of cored profiles is not as energetically onerous as previously claimed. DM particles in the cusp typically migrate to 2-3 core radii after absorbing a few percent of the energy released by SNe. The present-day slopes of the inner DM mass profiles, Gamma=d log M/dlogR=2.5-3, of the simulated dwarfs are similar to those measured in the luminous Fornax and Sculptor dwarf spheroids. None of the simulated galaxies has a circular velocity profile exceeding 20 km/s in the inner 1 kpc, implying that SN feedback is key to solve the "too-big-to-fail" problem for MW sub haloes.
1405.2666
An optical survey geometry of weak lensing survey: minimizing super-sample covariance
Takahashi, Soma, Takada, Kayo
The super-sample covariance (SSC) significantly degrade the statistical precision of WL PS measurement even for a wide-area survey. Using the 1000 mock realizations of the log-normal model, which approximates the WL field for a Lambda-domianted CDM, study an optical survey geometry to minimize the impact of SSC continuation. For a continuous survey geometry with a fixed survey area, a more elongated geometry such as a rectangular shape of 1:400 side-length ratio reduces the SSD effect and allows for a x2 improvement in the cumulative S/N of PS measurement up to l_max~ a few 1e3, compared to compact geometries such as squares or circles. When we allow the survey geometry to be disconnected but with a fixed total area, assuming 1x1 sq. degrees patches as the fundamental building blocks of survey footprints, the best strategy is to locate the patches with ~15degrees separations. This separation angel corresponds to the scale at which the 2pt correlation function as a negative minimum. The best configuration allows for a factor 100 gain in the effective area coverage as well as a factor 2.5 improvement in the S/N at high multipoles, yielding a much wider coverage of multipoles than in the compact geometry.
Nature
The different neighbors around Type-1 and Type-2 active galactic nuclei
Villaroel, Korn; Gaskell
Find strong differences in the color and AGN activity of the neighbors to type-1 and type-2 AGN, and in how the fraction of AGN residing in spiral hosts changes depending n the presence or not of a neighbor. These finding suggest that an evolutionary link between the two major AGN types might exist.
1405.2338
The SLUGGS survey: exploring the metallicity gradients of nearby early-type galaxies to large radii
Pastorello et al
Stellar metallicity gradients in the outer regions of galaxies are a critical tool for disentangling the contributions of in-situ and ex-situ formed stars. In the two-phase galaxy formation scenario, the initial gas collapse creates steep metallicity gradients, while the accretion of stars formed in satellites tends to flatten these gradients in the outskirts, particularly for massive galaxies. Obtain radial stellar metallicity profiles for 22 nearby early-type galaxies. From the Ca triplet lines in the NIR, measure the metallicity of the starlight up to 3 effective radii. Find a relation between the outer metallicity gradient and galaxy mass, in the sense that lower mass systems show steeper metallicity gradients than more massive galaxies. This result is consistent with a picture in which the ratio of ex-situ to in-situ formed stars is lower in less massive galaxies as a consequence of the smaller contribution by accretion. In addition, infer a correlation between the strength of the Ca triplet feature in the NIR and the stellar IMF slope that is consistent with recent models in the literature.
1405.2340
Is the effect of the sun's gravitational potential on dark matter particles observable?
Bozorgnia, Schwetz
Gravitational focusing (GF) is negligible for low masses; in the region of DM masses below 40 GeV an annual modulation signal can be established with a future direct detection experiment. Hard to establish the presence of GF from data. In the high-mass region where GF is more important the significance of annual modulation itself is very low.
1405.2577
Dark matter heating and early core formation in dwarf galaxies
Madau, Shen, Governato
Results from LCDM sims of a group of isolated dwarf galaxies that has been shown to reproduce the observed stellar mass and cold gas content, resolved SFHs, and metallicities of dwarfs in the Local Volume. Investigate the energetics and timetable of the cusp-core transformation. SNe-driven gas outflows remove DM cusps and create kpc-size cores in all systems having a stellar mass above 1e6 Msun. The "DM core mass removal efficiency" -- dark mass ejected per unit stellar mass -- ranges today from a few to a dozen, and increases with decreasing host mass. Because dwarfs form the bulk of their stars prior to z~1 and the amount of work required for DM heating and core formation scales approximately as Mvir^5/3, the unbinding of the DM cusp starts early and the formation of cored profiles is not as energetically onerous as previously claimed. DM particles in the cusp typically migrate to 2-3 core radii after absorbing a few percent of the energy released by SNe. The present-day slopes of the inner DM mass profiles, Gamma=d log M/dlogR=2.5-3, of the simulated dwarfs are similar to those measured in the luminous Fornax and Sculptor dwarf spheroids. None of the simulated galaxies has a circular velocity profile exceeding 20 km/s in the inner 1 kpc, implying that SN feedback is key to solve the "too-big-to-fail" problem for MW sub haloes.
1405.2666
An optical survey geometry of weak lensing survey: minimizing super-sample covariance
Takahashi, Soma, Takada, Kayo
The super-sample covariance (SSC) significantly degrade the statistical precision of WL PS measurement even for a wide-area survey. Using the 1000 mock realizations of the log-normal model, which approximates the WL field for a Lambda-domianted CDM, study an optical survey geometry to minimize the impact of SSC continuation. For a continuous survey geometry with a fixed survey area, a more elongated geometry such as a rectangular shape of 1:400 side-length ratio reduces the SSD effect and allows for a x2 improvement in the cumulative S/N of PS measurement up to l_max~ a few 1e3, compared to compact geometries such as squares or circles. When we allow the survey geometry to be disconnected but with a fixed total area, assuming 1x1 sq. degrees patches as the fundamental building blocks of survey footprints, the best strategy is to locate the patches with ~15degrees separations. This separation angel corresponds to the scale at which the 2pt correlation function as a negative minimum. The best configuration allows for a factor 100 gain in the effective area coverage as well as a factor 2.5 improvement in the S/N at high multipoles, yielding a much wider coverage of multipoles than in the compact geometry.
Sunday, May 11, 2014
Day 654
Monday.
1405.2070
Intra-cluster light at the frontier: Abell 2744
Montes, Trujillo
The ultra-deep multi wavelength HST Frontier Fields coverage of the Abell Cluster 2744 is used to derive the stellar population properties of its ICL. The rest frame colors of the ICL of this intermediate redshift (z=0.3064) massive cluster are bluer (g-r~0.7, i-J~0.6) than those found in the stellar populations of its main galaxy members (g-r~0.85; i-J~0.75). Based on these colors, derive the following mean metallicity Z~0.018pm0.003 for the ICL. The ICL age is ~3-5 Gyr younger than the average age of the massive galaxies of the cluster. The fraction of stellar mass in the ICL component comprises at least 6% of the total stellar mass of the galaxy cluster. Data is consistent with a scenario where the bulk of the ICL of Abell 2744 has been formed relatively recently (z<1). The stellar population properties of the ICL suggest that this diffuse component is mainly the result of the disruption of infalling galaxies with similar characteristics in mass (M*~3e10 Msun) and metallicity than the MW.
1405.2072
Missing black holes in brightest cluster galaxies as evidence for the occurrence of super kicks in nature
Gerosa, Sesana
SMBH can be kicked out because of the asymmetric gravitational wave emission (during a merger event) with kicks as large as ~5000 km/s, pushing the SMBHs out in the cluster outskirts for a time comparable to galaxy-evolution timescales. Measurements of SMBH occupation fraction can be used to observationally test the existence of super kicks in nature; BCGs are the ideal objects to explore this possibility. A single observational confirmation of a missing nuclear SMBH would provide strong evidence for the occurrence of super kicks in the strong-gravity regime of BH mergers.
1405.2070
Intra-cluster light at the frontier: Abell 2744
Montes, Trujillo
The ultra-deep multi wavelength HST Frontier Fields coverage of the Abell Cluster 2744 is used to derive the stellar population properties of its ICL. The rest frame colors of the ICL of this intermediate redshift (z=0.3064) massive cluster are bluer (g-r~0.7, i-J~0.6) than those found in the stellar populations of its main galaxy members (g-r~0.85; i-J~0.75). Based on these colors, derive the following mean metallicity Z~0.018pm0.003 for the ICL. The ICL age is ~3-5 Gyr younger than the average age of the massive galaxies of the cluster. The fraction of stellar mass in the ICL component comprises at least 6% of the total stellar mass of the galaxy cluster. Data is consistent with a scenario where the bulk of the ICL of Abell 2744 has been formed relatively recently (z<1). The stellar population properties of the ICL suggest that this diffuse component is mainly the result of the disruption of infalling galaxies with similar characteristics in mass (M*~3e10 Msun) and metallicity than the MW.
1405.2072
Missing black holes in brightest cluster galaxies as evidence for the occurrence of super kicks in nature
Gerosa, Sesana
SMBH can be kicked out because of the asymmetric gravitational wave emission (during a merger event) with kicks as large as ~5000 km/s, pushing the SMBHs out in the cluster outskirts for a time comparable to galaxy-evolution timescales. Measurements of SMBH occupation fraction can be used to observationally test the existence of super kicks in nature; BCGs are the ideal objects to explore this possibility. A single observational confirmation of a missing nuclear SMBH would provide strong evidence for the occurrence of super kicks in the strong-gravity regime of BH mergers.
Day 653
Sunday.
1401.7017
Calcium-rich gap transients: solving the Calcium Conundrum in the intracluster medium
Mulchaey, Kasliwal, Kollmeier
The abundance of Ca in ICM is higher than expected using models for core-collapse and Type Ia SNe alone, but can be alleviated by including a contribution from the recently discovered subclass of SNe known as Ca-rich gap transients. These SNe type seem to be associated with intracluster stars, and not individual galaxies.
1401.7022
Inflationary freedom and cosmological neutrino constraints
de Putter, Linder, Mishra
Massive relic neutrinos affect the expansion history of the universe and lead to a suppression of matter clustering on scales smaller than the associated free streaming length, but the resulting effect on cosmological perturbations is relative to the primordial PS of density perturbations from inflation, so freedom in the primordial PS affects neutrino mass constraints. Using measurements of the CMB, the galaxy PS and the Hubble constant, constrain neutrino mass and number of species for a model independent primordial PS. Describing the primordial PS by a 20-node spline, find that the neutrino mass upper limit is a factor 3 weaker than when a power law form is imposed, if only CMB data are used. The primordial PS itself is constrained to better than 10% in the wave vector range k~0.01-0.25 Mpc^-2. Galaxy clustering data and a determination of the Hubble constant play a key role in reining in the effects of inflationary freedom on neutrino constraints. The inclusion of both eliminates the inflationary freedom degradation of the neutrino mass bound, giving for the sum of neutrino masses Sum m_nu< 0.18 eV (at 95% CL, Planck+BOSS+H0), approximately independent of the assumed primordial PS model. When allowing for a free effective number of species, N_eff, the joint constraints on Sum m_nu and N_eff are loosened by a factor 1.7 when the power law form of the primordial PS is abandoned in favor of the spline parameterization.
1401.7051
A CMB lensing-galaxy intrinsic alignment contaminant to gravitational lensing cross-correlated probes of the universe and a proposal for calibration
Troxel, Ishak
Introduce a cross-correlation term between CMB lensing and IA (phi I). This effect acts as a contaminant to the cross-correlation between CMB lensing and galaxy lensing. The latter cross-correlation has recently been detected for the first time, and measurements will greatly improve as the area of overlap between galaxy and CMB surveys increases and measurement of the CMB polarization become more significant. This will constitute a powerful probe for studying the structure and evolution of the universe. The magnitude of the phi I term is found to be about 15% of the pure CMB lensing-galaxy lensing component and acts to reduce the magnitude of its measured spectrum. This offset in the spectrum will strongly impact its use for precision cosmological study if left unmitigated. Also propose a method to calibrate this phi I contamination through use of a scaling relation that allows one to reduce the impact of phi I by a factor of 20 or more in all redshift bins, which would reduce its magnitude down to detection limits in almost all cases. This will allow the full use of this probe for precision cosmology.
1401.7221
Tides, planetary companions, and habitability: Habitability in the habitable zone of low-mass stars
Van Laerhoven, Barnes, Greenberg
Earth-scale planets in the classical HZ are more likely to be habitable if they possess active geophysics [because O, N, S, P, gets replenished from the planet itself into the presumably existing liquid water; rotating Fe core in the molten earth generates B-fields that deflect harmful CRs; and stabilizes the temperature by C recycling into the crust]. Without a constant internal energy source, planets cool as they age, eventually terminating tectonic activity and rendering the planet sterile to life [in Earth, at least some of the heat is maintained from radioactive decay of elements in the molten core, though]. However, for planets orbiting low-mass stars, the presence of an outer companion could generate enough tidal heat in the HZ planet to prevent such cooling. The range of mass and orbital parameters for the companion that give adequate long-term heating of the inner HZ planet, while avoiding very early total desiccation, is probably substantial. Locate the ideal location for the outer of a pair of planets, under the assumption that they inner planet has the same incident flux as Earth, orbiting example stars: a generic late M dwarf (Teff=2670K) and the M9V/L0 dwarf DEN1048. Thus discoveries of Earth-scale planets in the HZ zone of old small stars should be followed by searches for outer companion planets that might be essential for current habitability.
1401.7017
Calcium-rich gap transients: solving the Calcium Conundrum in the intracluster medium
Mulchaey, Kasliwal, Kollmeier
The abundance of Ca in ICM is higher than expected using models for core-collapse and Type Ia SNe alone, but can be alleviated by including a contribution from the recently discovered subclass of SNe known as Ca-rich gap transients. These SNe type seem to be associated with intracluster stars, and not individual galaxies.
1401.7022
Inflationary freedom and cosmological neutrino constraints
de Putter, Linder, Mishra
Massive relic neutrinos affect the expansion history of the universe and lead to a suppression of matter clustering on scales smaller than the associated free streaming length, but the resulting effect on cosmological perturbations is relative to the primordial PS of density perturbations from inflation, so freedom in the primordial PS affects neutrino mass constraints. Using measurements of the CMB, the galaxy PS and the Hubble constant, constrain neutrino mass and number of species for a model independent primordial PS. Describing the primordial PS by a 20-node spline, find that the neutrino mass upper limit is a factor 3 weaker than when a power law form is imposed, if only CMB data are used. The primordial PS itself is constrained to better than 10% in the wave vector range k~0.01-0.25 Mpc^-2. Galaxy clustering data and a determination of the Hubble constant play a key role in reining in the effects of inflationary freedom on neutrino constraints. The inclusion of both eliminates the inflationary freedom degradation of the neutrino mass bound, giving for the sum of neutrino masses Sum m_nu< 0.18 eV (at 95% CL, Planck+BOSS+H0), approximately independent of the assumed primordial PS model. When allowing for a free effective number of species, N_eff, the joint constraints on Sum m_nu and N_eff are loosened by a factor 1.7 when the power law form of the primordial PS is abandoned in favor of the spline parameterization.
1401.7051
A CMB lensing-galaxy intrinsic alignment contaminant to gravitational lensing cross-correlated probes of the universe and a proposal for calibration
Troxel, Ishak
Introduce a cross-correlation term between CMB lensing and IA (phi I). This effect acts as a contaminant to the cross-correlation between CMB lensing and galaxy lensing. The latter cross-correlation has recently been detected for the first time, and measurements will greatly improve as the area of overlap between galaxy and CMB surveys increases and measurement of the CMB polarization become more significant. This will constitute a powerful probe for studying the structure and evolution of the universe. The magnitude of the phi I term is found to be about 15% of the pure CMB lensing-galaxy lensing component and acts to reduce the magnitude of its measured spectrum. This offset in the spectrum will strongly impact its use for precision cosmological study if left unmitigated. Also propose a method to calibrate this phi I contamination through use of a scaling relation that allows one to reduce the impact of phi I by a factor of 20 or more in all redshift bins, which would reduce its magnitude down to detection limits in almost all cases. This will allow the full use of this probe for precision cosmology.
1401.7221
Tides, planetary companions, and habitability: Habitability in the habitable zone of low-mass stars
Van Laerhoven, Barnes, Greenberg
Earth-scale planets in the classical HZ are more likely to be habitable if they possess active geophysics [because O, N, S, P, gets replenished from the planet itself into the presumably existing liquid water; rotating Fe core in the molten earth generates B-fields that deflect harmful CRs; and stabilizes the temperature by C recycling into the crust]. Without a constant internal energy source, planets cool as they age, eventually terminating tectonic activity and rendering the planet sterile to life [in Earth, at least some of the heat is maintained from radioactive decay of elements in the molten core, though]. However, for planets orbiting low-mass stars, the presence of an outer companion could generate enough tidal heat in the HZ planet to prevent such cooling. The range of mass and orbital parameters for the companion that give adequate long-term heating of the inner HZ planet, while avoiding very early total desiccation, is probably substantial. Locate the ideal location for the outer of a pair of planets, under the assumption that they inner planet has the same incident flux as Earth, orbiting example stars: a generic late M dwarf (Teff=2670K) and the M9V/L0 dwarf DEN1048. Thus discoveries of Earth-scale planets in the HZ zone of old small stars should be followed by searches for outer companion planets that might be essential for current habitability.
Saturday, May 10, 2014
Day 652
Saturday.
1401.6456
A rapid evolving region in the galactic center: why S-stars thermalize and more massive stars are missing
Chen, Amaro-Seoane
The observed population of "S-stars" within a distance of 1" from SgrA* contradicts the understanding of star formation, due to the forbiddingly violent environment. A suggested possibility is that these stars form far and have been brought by some fast dynamical process, since they are young. Nonetheless, all conjectured mechanisms either fail to reproduce their eccentricities -- without resorting to extra ingredients, which render the models more complicated -- or cannot explain the problem of "inverse mass segregation" at the Galactic Center: the fact that lighter stars are closer to the center (the S-stars) and more massive ones, WR and O-stars, father out. In this Letter, put forward the idea that the responsible for both, the distribution of the eccentricities and the paucity of massive stars, in an induced Kozai-Lidov-like resonance exerted by the observed disk on the stars populating the innermost 1" region, considering that the disk probably extended to smaller radius in the past.
1401.6459
The Local Void: for or against $\Lambda$CDM?
Xie, Gao, Guo
The emptiness of the Local Void has been put forward as a serious challenge to the current standard paradigm of structure formation in LCDM. Use a high resolution cosmological N-body sim, the Millennium-II run, combined with a sophisticated SAM, to explore statistically whether the local void is allowed within the current knowledge of galaxy formation in LCDM. Find that about 15% of the LG analogue systems (11 of 77) in the simulation are associated with nearby low density regions having size and 'emptiness' similar to those of the observed Local Void. This suggests that, rather than a crisis of the LCDM, the emptiness of the Local Void is indeed a success of the standard LCDM theory. The paucity of faint galaxies in such voids results from a combination of two factors: a lower amplitude of the halo mass function in the voids than in the field, and a lower galaxy formation efficiency in void haloes due to halo assembly bias effects. While the former is the dominating factor, the latter also plays a sizable role. The halo assembly bias effect results in a stellar mass fraction 25% lower for void galaxies when compared to field galaxies with the same halo mass.
1401.6842
3d cosmic shear: cosmology from CFHTLenS
Kitching et al
Present the first application of 3d cosmic shear to a wide-field WL survey. 3d cosmic shear is a technique that analyses WL in 3d using a spherical harmonic approach, and does not bin data in the redshift direction. This is applied to CFHTLenS, a 154 square degree imaging survey wit ha median redshift of 0.7 and an effective number density of 11 galaxies per square arc minute usable for WL. To account for survey masks, apply a 3d pseudo-Cl approach on WL data, and to avoid uncertainties in the highly NL regime, separately analyze radial wave numbers k<=1.5h/Mpc and k>=5.0h/Mpc, and angular wave numbers l~400-5000. Show how one can recover 2d and tomographic PS from the full 3d cosmic shear PS and present a measurement of the 2d cosmic shear power spectrum, and measurements of a set of 2-bin and 6-bin cosmic shear tomographic PS; in doing so, find that using the 3d power in the calculation of such 2d and tomographic PS from data naturally accounts for a minimum scale in the matter PS. Use 3d cosmic shear to constrain cosmologies with parameters OmegaM, OmegaB, sigma8, h, ns, w0, wa. For a non-evolving DE EoS, and assuming a flat cosmology, lensing combined with WMAP7 results in h=0.78pm0.12, OmeagM=0.252pm0.079, sigma8=0.88pm0.23, and w=-1.16pm0.38 using only scales k<=1.5h/Mpc. Also present results of lensing combined with first year Planck results, where no tension is found with the results form this analysis, but also find no significant improvement over the Planck results alone. Find evidence of a suppression of power compared to LCDM on small scales 1.5<k<=5.0h/Mpc in the lensing data, which is consistent with predictions of the effect of baryonic feedback on the matter PS.
1401.6456
A rapid evolving region in the galactic center: why S-stars thermalize and more massive stars are missing
Chen, Amaro-Seoane
The observed population of "S-stars" within a distance of 1" from SgrA* contradicts the understanding of star formation, due to the forbiddingly violent environment. A suggested possibility is that these stars form far and have been brought by some fast dynamical process, since they are young. Nonetheless, all conjectured mechanisms either fail to reproduce their eccentricities -- without resorting to extra ingredients, which render the models more complicated -- or cannot explain the problem of "inverse mass segregation" at the Galactic Center: the fact that lighter stars are closer to the center (the S-stars) and more massive ones, WR and O-stars, father out. In this Letter, put forward the idea that the responsible for both, the distribution of the eccentricities and the paucity of massive stars, in an induced Kozai-Lidov-like resonance exerted by the observed disk on the stars populating the innermost 1" region, considering that the disk probably extended to smaller radius in the past.
1401.6459
The Local Void: for or against $\Lambda$CDM?
Xie, Gao, Guo
The emptiness of the Local Void has been put forward as a serious challenge to the current standard paradigm of structure formation in LCDM. Use a high resolution cosmological N-body sim, the Millennium-II run, combined with a sophisticated SAM, to explore statistically whether the local void is allowed within the current knowledge of galaxy formation in LCDM. Find that about 15% of the LG analogue systems (11 of 77) in the simulation are associated with nearby low density regions having size and 'emptiness' similar to those of the observed Local Void. This suggests that, rather than a crisis of the LCDM, the emptiness of the Local Void is indeed a success of the standard LCDM theory. The paucity of faint galaxies in such voids results from a combination of two factors: a lower amplitude of the halo mass function in the voids than in the field, and a lower galaxy formation efficiency in void haloes due to halo assembly bias effects. While the former is the dominating factor, the latter also plays a sizable role. The halo assembly bias effect results in a stellar mass fraction 25% lower for void galaxies when compared to field galaxies with the same halo mass.
1401.6842
3d cosmic shear: cosmology from CFHTLenS
Kitching et al
Present the first application of 3d cosmic shear to a wide-field WL survey. 3d cosmic shear is a technique that analyses WL in 3d using a spherical harmonic approach, and does not bin data in the redshift direction. This is applied to CFHTLenS, a 154 square degree imaging survey wit ha median redshift of 0.7 and an effective number density of 11 galaxies per square arc minute usable for WL. To account for survey masks, apply a 3d pseudo-Cl approach on WL data, and to avoid uncertainties in the highly NL regime, separately analyze radial wave numbers k<=1.5h/Mpc and k>=5.0h/Mpc, and angular wave numbers l~400-5000. Show how one can recover 2d and tomographic PS from the full 3d cosmic shear PS and present a measurement of the 2d cosmic shear power spectrum, and measurements of a set of 2-bin and 6-bin cosmic shear tomographic PS; in doing so, find that using the 3d power in the calculation of such 2d and tomographic PS from data naturally accounts for a minimum scale in the matter PS. Use 3d cosmic shear to constrain cosmologies with parameters OmegaM, OmegaB, sigma8, h, ns, w0, wa. For a non-evolving DE EoS, and assuming a flat cosmology, lensing combined with WMAP7 results in h=0.78pm0.12, OmeagM=0.252pm0.079, sigma8=0.88pm0.23, and w=-1.16pm0.38 using only scales k<=1.5h/Mpc. Also present results of lensing combined with first year Planck results, where no tension is found with the results form this analysis, but also find no significant improvement over the Planck results alone. Find evidence of a suppression of power compared to LCDM on small scales 1.5<k<=5.0h/Mpc in the lensing data, which is consistent with predictions of the effect of baryonic feedback on the matter PS.
Friday, May 9, 2014
Day 651
Friday.
1405.1414
Stars as resonant absorbers of gravitational waves
McKernan, Ford, Kocsis, Haiman
Quadrupole oscillation modes in stars can resonate with indecent GWs, and grow NL at the expense of GW energy. Stars near MBHB (massive BH binaries) can act as GW-charged batteries, cooling radiatively. Mass-loss from these stars can prompt MBHB accretion at near-Eddington rates. GW opacity is independent of amplitude, so distant resonating stars can eclipse GW sources. Absorption by the Sun of GWs from Galactic WD binaries may be detectable with second-generation space-based GW detectors as a shadow within a complex diffraction pattern.
1405.1418
Properties of galaxies reproduced by a hydrodynamic simulation
Vogelsberger, … Springel, Xu, Hernquist, et al
Previous simulations of cosmic structures failed to create a mixed population of elliptical and spiral galaxies due to numerical inaccuracies and incomplete physical models. Because of computational constraints, they were unable to track the small locale evolution of gas and stars to the present epoch within a representative portion of the Universe. Report a simulation that starts 12 Myrs after BB, and traces 13 Byrs of cosmic evolution with 12 billion resolution elements in a volume of (106.5Mpc)^3. Yields a reasonable population of ellipticals and spirals, reproduces the distribution of galaxies in clusters and statistics of hydrogen on large scales, and at the same time the metal and hydrogen content of galaxies on small scales.
1405.1427
Gone with the wind: where is the missing stellar wind energy from massive star clusters?
Rosen et al
Star clusters larger than ~1e3 Msun contain multiple hot stars that launch fast stellar winds. The integrated kinetic energy carried by these winds is comparable to that delivered by SN explosions, suggesting that at early times winds could be an important form of feedback on the surrounding cold material from which the star cluster formed. However, the interaction of these winds with the surrounding clumpy, turbulent, cold gas is complex and poorly understood. Investigate this problem via an accounting exercise: use empirically determined properties of four well-studied massive stars clusters to determine where the energy injected by stellar winds ultimately ends up. Consider a range of kinetic energy loss channels, including radiative cooling, mechanical work on the cold interstellar medium, thermal conduction, heating of dust via collisions by the hot gas, and bulk advection of thermal energy by the hot gas. Show that, for at least some of the clusters, none of these channels can account for more than a small fraction of the injected energy. Suggest that turbulent mixing at the hot-cold interface or physical leakage of the hot gas from the HII region can efficiently remove the kinetic energy injected by the massive stars in young star clusters. Even for the clusters where it is able to account for all the injected kinetic energy, show that accounting sets strong constraints on the importance of stellar winds as a mechanism for feedback on the cold ISM.
1405.1432
Delensing galaxy surveys
Chang, Jain
WL can cause displacements, magnification, rotation and shearing of the images of distant galaxies. Most studies focus on the shear and magnification effects since they are more easily observed. IN this paper, focus on the feet of lensing displacements on wide field images. Galaxies at 0.5<z<1 are typically displaced by 1 arc minute, and the displiacemtns are cohenereng over degree-size patches. HOwever the displacement effect is z-dependent, so there is a visible relative shift between galaxies at different redshifts, even if they are close on the sky. SHow that the reconstruction of the original galaxy position is now feasible with lensing surveys that cover many hundreds of square degrees. Test with simulations two approaches to "delensing": one uses shear measurements and the other uses the FG galaxy distribution as a proxy for the mass. Also estimate the effect of FG deflections on gg lensing measurements and find it is relevant only for LSST and Euclid-era surveys.
1405.1447
Understanding higher-order nonlocal halo bias at large scales by combining the power spectrum with the bispectrum
Saito, Baldauf, Vlah, Seljak, Okumura, McDonald
Understanding the relation between underlying matter distriubiton and biased tracers such as galaxy or DM halo is essential to extract cosmological information from ongoing or future galaxy redshift surveys. At sufficiently large scales such as the BAO scale, a standard approach for the bias problem on the basis of the PT is to assume the 'local bias' model in which the density field of biased tracers is deterministically expanded in terms of matter density field at the same position. The higher-order bias parameters are then determined by combining the PS with higher-order statistics such as the bispectrum. As is pointed out by recent studies, however, NL gravitational evolution naturally includes nonlocal bias terms even if initially starting only with purely local bias. Previous works showed that the second-order nonlocal bias term, which corresponds to the gravitational tidal field, is important to explain the characteristic scale-dependence of the bispectrum. In this paper, extend the non-local bias term up to 3rd order, and investigate whether the PT-based model including NL bias terms can simultaneously explain the PS and the bispectrum of simulated haloes in N-body simulations. Show that the PS, including density and momentum, and the bispectrum between halo and matter in N-body simulations can be simultaneously well explained by the model including up to 3rd order nonlocal bias terms up to k~0.1h/Mpc. Also, the results seem in a good agreement with theoretical predictions of a simple coevolution picture, although the agreement is not perfect. These demonstration clearly shows a failure of the local bias model even at such large scales, and conclude that nonlocal bias terms should be consistently included in order to model statistics of haloes.
1405.1539
A new method of weak lensing shear measurement using 0th order ellipticity and ERA
Okura, Futamase
Developed a new method for WL shear analysis using the ellipticity defined by the 0th order moment of the image and a new method of PSF correction called the ERA method. Although there is a strong correlation between the ellipticity calculated using this approach and the usual ellipticity defined by the 2nd order moment, the ellipticity calculated here has a higher S/N ratio because it is weighted to the central region of the image. These results were confirmed using data for A1689 from the Subaru telescope. The new PSF correction technique developed is also applied here, which uses an artificial image with the same ellipticity as the lensed images, and avoids the systematic error associated with the approximation used in previous approaches for PSF correction. Therefore it is expected that this new method measures the shear more accurately than the previous moment method. Tested and confirmed this expectation using simulated images.
1405.1566
Detection of a super void aligned with the cold spot of the cosmic microwave background
Szapudi et al
Use the WISE-2MASS IR galaxy catalog matched with PS1 galaxies to search for a super void in the direction of the CMB cold spot. Imaging catalog has median z~0.14, and we obtain photometric z from PS1 optical colors to create a tomographic map of the galaxy distribution. The radial profile centered on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous CMB results, test for under densities within two angular radii, 5 and 15 deg. The counts in photo-z bins show significantly low densities at high significance, >5 sigma and >6 sigma, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is z~0.15-0.25. Data combined with an earlier measurement are consistent with a large R_void=192pm15 Mpc/h (2sigma) super void with delta~-0.13pm0.03 centered at z=0.22pm0.01. Such a super void, constituting a ~3.5-5 sigma fluctuation in a Gaussian distribution of the LCDM model, is a plausible cause for the Cold Spot.
1405.1604
Jupiter as a giant cosmic ray detector
RImmer, Stark, Helling
In order to be observed, air showers in Jupiter's atmosphere would need to be oriented toward the Earth, and would need to occur sufficiently high in the atmosphere that the gamma rays an penetrate. Demonstrate that under these assumptions, Jupiter provides an effective CR "detector" area of 3.3e7 km^2. Predict that Fermi-LAT should be able to detect events of energy>1e21 eV with fluence 1e-7 erg/cm2 at a rate of about one per month. THe observed number of air showers may provide an indirect measure of the flux of CRs > 1e20 eV. Extensive air showers also produce a synchrotron signature that may be measurable by ALMA. Simultaneous observations of Jupiter with ALMA and Fermi-LAT could be used to provide broad constraints on the energies of the initiating CRs.
1405.1910
Optical spectra of 73 stripped-envelope core-collapse supernovae
Modjaz, et al
Present 645 optical spectra of 73 SNe of types IIb, Ib, Ic and broad-lined Ic. All of these types are attributed to the core collapse of massive stars, with varying degrees of intact H and He envelopes before explosion. The SNe in the sample have a mean redshift <cz>=4200 km/s. Most of these spectra were gathered at the Harvard-Smithsonian CfA between 2004 and 2009. For 53 SNe, these are the first published spectra. The data coverage range from mere identification (1-3 spectra) for a few SNe to extensive series of observations (10-30 spectra) that trace the spectral evolution for others, with an average of 9 spectra per SN. For 44 SNe of the 73 SNe presented here, have well-determined dates of maximum light to determine the phase of each spectrum. Sample constitutes the most extensive spectral library of stripped-envelope SNe to date. Provide very early coverage (as early as 30 days before V-band max) for photospheric spectra, as well as late-time nebular coverage when the innermost regions of the SNe are visible (as late as 2 years after explosion, while for SN1993J, there are data as late as 11.6 years). This data set has homogeneous observations and reductions that allow us to study the spectroscopic diversity of these classes of stripped SNe and to compare these to SNe associated with gamma-ray bursts. Undertake these matters in follow-up papers.
1405.2020
Generalized slow roll for tensors
Hu
The recent BICEP2 detection of degree scale CMB B-mode polarization, coupled with a deficit of observed power in large angle temperature anisotropy, suggest that the slow-roll parameter epsilon_H, the fractional variation in the Hubble rate per e-fold, is both relatively large and may evolve from an even larger value on scales greater than the horizon at recombination. The relatively large tensor contribution implied also requires finite matching features in the tensor PS for any scalar PS feature proposed to explain anomalies in the temperature data. Extend the generalized slow-roll approach for computing power spectra, appropriate for such models where the slow-roll parameters vary, to tensor features where scalar features are large. This approach also generalizes the tensor-scalar consistency relation to be between the ratio of tensor and scalar sources and features in the two power spectra. Features in the tensor spectrum are generically suppressed by e_H relative those in the scalar spectrum and by the smoothness of the Hubble rate, which must obey covariant conservation of energy, versus its derivatives. Their detection in near future CMB data would indicate a fast roll period of inflation where e_H approaches order unity, allowed but not required by inflationary explanations of temperature anomalies.
1405.2035
Shape profiles and orientation bias for weak and strong lensing cluster haloes
Groener, Goldberg
Study the intrinsic shape and alignment of isodensities of galaxy cluster haloes extracted from the MultiDark MDR1 cosmological simulation. Find that the simulated haloes are extremely prolate on small scales, and increasingly spherical on larger ones. Due to this trend, projection along the LoS produces an overestimate of the concentration index as a decreasing function of radius. Based on this result, predict that the selection of clusters based upon their strong lensing features will tend to produce a larger over-concentration bias when compared with WL of this same population, a difference of ~17%. Isodensities are found to be fairly well-aligned throughout the entirety of the radial scale of each halo population. However, major axes of individual halos have been found to deviate by as much as ~30deg. Also present a value-added catalog of our analysis results, which have made publicly available to download.
1405.1414
Stars as resonant absorbers of gravitational waves
McKernan, Ford, Kocsis, Haiman
Quadrupole oscillation modes in stars can resonate with indecent GWs, and grow NL at the expense of GW energy. Stars near MBHB (massive BH binaries) can act as GW-charged batteries, cooling radiatively. Mass-loss from these stars can prompt MBHB accretion at near-Eddington rates. GW opacity is independent of amplitude, so distant resonating stars can eclipse GW sources. Absorption by the Sun of GWs from Galactic WD binaries may be detectable with second-generation space-based GW detectors as a shadow within a complex diffraction pattern.
1405.1418
Properties of galaxies reproduced by a hydrodynamic simulation
Vogelsberger, … Springel, Xu, Hernquist, et al
Previous simulations of cosmic structures failed to create a mixed population of elliptical and spiral galaxies due to numerical inaccuracies and incomplete physical models. Because of computational constraints, they were unable to track the small locale evolution of gas and stars to the present epoch within a representative portion of the Universe. Report a simulation that starts 12 Myrs after BB, and traces 13 Byrs of cosmic evolution with 12 billion resolution elements in a volume of (106.5Mpc)^3. Yields a reasonable population of ellipticals and spirals, reproduces the distribution of galaxies in clusters and statistics of hydrogen on large scales, and at the same time the metal and hydrogen content of galaxies on small scales.
1405.1427
Gone with the wind: where is the missing stellar wind energy from massive star clusters?
Rosen et al
Star clusters larger than ~1e3 Msun contain multiple hot stars that launch fast stellar winds. The integrated kinetic energy carried by these winds is comparable to that delivered by SN explosions, suggesting that at early times winds could be an important form of feedback on the surrounding cold material from which the star cluster formed. However, the interaction of these winds with the surrounding clumpy, turbulent, cold gas is complex and poorly understood. Investigate this problem via an accounting exercise: use empirically determined properties of four well-studied massive stars clusters to determine where the energy injected by stellar winds ultimately ends up. Consider a range of kinetic energy loss channels, including radiative cooling, mechanical work on the cold interstellar medium, thermal conduction, heating of dust via collisions by the hot gas, and bulk advection of thermal energy by the hot gas. Show that, for at least some of the clusters, none of these channels can account for more than a small fraction of the injected energy. Suggest that turbulent mixing at the hot-cold interface or physical leakage of the hot gas from the HII region can efficiently remove the kinetic energy injected by the massive stars in young star clusters. Even for the clusters where it is able to account for all the injected kinetic energy, show that accounting sets strong constraints on the importance of stellar winds as a mechanism for feedback on the cold ISM.
1405.1432
Delensing galaxy surveys
Chang, Jain
WL can cause displacements, magnification, rotation and shearing of the images of distant galaxies. Most studies focus on the shear and magnification effects since they are more easily observed. IN this paper, focus on the feet of lensing displacements on wide field images. Galaxies at 0.5<z<1 are typically displaced by 1 arc minute, and the displiacemtns are cohenereng over degree-size patches. HOwever the displacement effect is z-dependent, so there is a visible relative shift between galaxies at different redshifts, even if they are close on the sky. SHow that the reconstruction of the original galaxy position is now feasible with lensing surveys that cover many hundreds of square degrees. Test with simulations two approaches to "delensing": one uses shear measurements and the other uses the FG galaxy distribution as a proxy for the mass. Also estimate the effect of FG deflections on gg lensing measurements and find it is relevant only for LSST and Euclid-era surveys.
1405.1447
Understanding higher-order nonlocal halo bias at large scales by combining the power spectrum with the bispectrum
Saito, Baldauf, Vlah, Seljak, Okumura, McDonald
Understanding the relation between underlying matter distriubiton and biased tracers such as galaxy or DM halo is essential to extract cosmological information from ongoing or future galaxy redshift surveys. At sufficiently large scales such as the BAO scale, a standard approach for the bias problem on the basis of the PT is to assume the 'local bias' model in which the density field of biased tracers is deterministically expanded in terms of matter density field at the same position. The higher-order bias parameters are then determined by combining the PS with higher-order statistics such as the bispectrum. As is pointed out by recent studies, however, NL gravitational evolution naturally includes nonlocal bias terms even if initially starting only with purely local bias. Previous works showed that the second-order nonlocal bias term, which corresponds to the gravitational tidal field, is important to explain the characteristic scale-dependence of the bispectrum. In this paper, extend the non-local bias term up to 3rd order, and investigate whether the PT-based model including NL bias terms can simultaneously explain the PS and the bispectrum of simulated haloes in N-body simulations. Show that the PS, including density and momentum, and the bispectrum between halo and matter in N-body simulations can be simultaneously well explained by the model including up to 3rd order nonlocal bias terms up to k~0.1h/Mpc. Also, the results seem in a good agreement with theoretical predictions of a simple coevolution picture, although the agreement is not perfect. These demonstration clearly shows a failure of the local bias model even at such large scales, and conclude that nonlocal bias terms should be consistently included in order to model statistics of haloes.
1405.1539
A new method of weak lensing shear measurement using 0th order ellipticity and ERA
Okura, Futamase
Developed a new method for WL shear analysis using the ellipticity defined by the 0th order moment of the image and a new method of PSF correction called the ERA method. Although there is a strong correlation between the ellipticity calculated using this approach and the usual ellipticity defined by the 2nd order moment, the ellipticity calculated here has a higher S/N ratio because it is weighted to the central region of the image. These results were confirmed using data for A1689 from the Subaru telescope. The new PSF correction technique developed is also applied here, which uses an artificial image with the same ellipticity as the lensed images, and avoids the systematic error associated with the approximation used in previous approaches for PSF correction. Therefore it is expected that this new method measures the shear more accurately than the previous moment method. Tested and confirmed this expectation using simulated images.
1405.1566
Detection of a super void aligned with the cold spot of the cosmic microwave background
Szapudi et al
Use the WISE-2MASS IR galaxy catalog matched with PS1 galaxies to search for a super void in the direction of the CMB cold spot. Imaging catalog has median z~0.14, and we obtain photometric z from PS1 optical colors to create a tomographic map of the galaxy distribution. The radial profile centered on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous CMB results, test for under densities within two angular radii, 5 and 15 deg. The counts in photo-z bins show significantly low densities at high significance, >5 sigma and >6 sigma, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is z~0.15-0.25. Data combined with an earlier measurement are consistent with a large R_void=192pm15 Mpc/h (2sigma) super void with delta~-0.13pm0.03 centered at z=0.22pm0.01. Such a super void, constituting a ~3.5-5 sigma fluctuation in a Gaussian distribution of the LCDM model, is a plausible cause for the Cold Spot.
1405.1604
Jupiter as a giant cosmic ray detector
RImmer, Stark, Helling
In order to be observed, air showers in Jupiter's atmosphere would need to be oriented toward the Earth, and would need to occur sufficiently high in the atmosphere that the gamma rays an penetrate. Demonstrate that under these assumptions, Jupiter provides an effective CR "detector" area of 3.3e7 km^2. Predict that Fermi-LAT should be able to detect events of energy>1e21 eV with fluence 1e-7 erg/cm2 at a rate of about one per month. THe observed number of air showers may provide an indirect measure of the flux of CRs > 1e20 eV. Extensive air showers also produce a synchrotron signature that may be measurable by ALMA. Simultaneous observations of Jupiter with ALMA and Fermi-LAT could be used to provide broad constraints on the energies of the initiating CRs.
1405.1910
Optical spectra of 73 stripped-envelope core-collapse supernovae
Modjaz, et al
Present 645 optical spectra of 73 SNe of types IIb, Ib, Ic and broad-lined Ic. All of these types are attributed to the core collapse of massive stars, with varying degrees of intact H and He envelopes before explosion. The SNe in the sample have a mean redshift <cz>=4200 km/s. Most of these spectra were gathered at the Harvard-Smithsonian CfA between 2004 and 2009. For 53 SNe, these are the first published spectra. The data coverage range from mere identification (1-3 spectra) for a few SNe to extensive series of observations (10-30 spectra) that trace the spectral evolution for others, with an average of 9 spectra per SN. For 44 SNe of the 73 SNe presented here, have well-determined dates of maximum light to determine the phase of each spectrum. Sample constitutes the most extensive spectral library of stripped-envelope SNe to date. Provide very early coverage (as early as 30 days before V-band max) for photospheric spectra, as well as late-time nebular coverage when the innermost regions of the SNe are visible (as late as 2 years after explosion, while for SN1993J, there are data as late as 11.6 years). This data set has homogeneous observations and reductions that allow us to study the spectroscopic diversity of these classes of stripped SNe and to compare these to SNe associated with gamma-ray bursts. Undertake these matters in follow-up papers.
1405.2020
Generalized slow roll for tensors
Hu
The recent BICEP2 detection of degree scale CMB B-mode polarization, coupled with a deficit of observed power in large angle temperature anisotropy, suggest that the slow-roll parameter epsilon_H, the fractional variation in the Hubble rate per e-fold, is both relatively large and may evolve from an even larger value on scales greater than the horizon at recombination. The relatively large tensor contribution implied also requires finite matching features in the tensor PS for any scalar PS feature proposed to explain anomalies in the temperature data. Extend the generalized slow-roll approach for computing power spectra, appropriate for such models where the slow-roll parameters vary, to tensor features where scalar features are large. This approach also generalizes the tensor-scalar consistency relation to be between the ratio of tensor and scalar sources and features in the two power spectra. Features in the tensor spectrum are generically suppressed by e_H relative those in the scalar spectrum and by the smoothness of the Hubble rate, which must obey covariant conservation of energy, versus its derivatives. Their detection in near future CMB data would indicate a fast roll period of inflation where e_H approaches order unity, allowed but not required by inflationary explanations of temperature anomalies.
1405.2035
Shape profiles and orientation bias for weak and strong lensing cluster haloes
Groener, Goldberg
Study the intrinsic shape and alignment of isodensities of galaxy cluster haloes extracted from the MultiDark MDR1 cosmological simulation. Find that the simulated haloes are extremely prolate on small scales, and increasingly spherical on larger ones. Due to this trend, projection along the LoS produces an overestimate of the concentration index as a decreasing function of radius. Based on this result, predict that the selection of clusters based upon their strong lensing features will tend to produce a larger over-concentration bias when compared with WL of this same population, a difference of ~17%. Isodensities are found to be fairly well-aligned throughout the entirety of the radial scale of each halo population. However, major axes of individual halos have been found to deviate by as much as ~30deg. Also present a value-added catalog of our analysis results, which have made publicly available to download.
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