Friday.
1512.09142
Campaign 9 of the $K2$ mission: observational parameters, scientific drivers, and community involvement for a simultaneous space- and ground-based microlensing survey
Henderson, et al
K2C9 will conduct a ~3.4 deg2 survey toward the Galactic bulge from 7/April through 1/Juy of 2016 that will leverage the spatial separation between K2 and the Earth to facilitate measurement of the microlens parallax pi_E for >120 microlensing events, including several planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These satellite parallax measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems. In this white paper, provide an overview of the K2C9 space- and ground-based microlensing survey. Specifically detail the demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of K2C9,, and the array of ground-based resources dedicated to concurrent observations. Finally outline the avenues through which the larger community can become involved, and generally encourage participation in K2C9, which constitutes an important pathfinding mission and community exercise in anticipation of WFIRST.
Thursday, December 31, 2015
Day 1031
1512.08800
Gravitational potential wells and the cosmic bulk flow
Kumar, Wang, Feldman, Watkins
The bulk flow is a volume average of the peculiar velocities and a useful probe of the mass distribution on large scales. The gravitational instability model view the bulk flow as a potential flow that obeys a Maxwellian Distribution. Use two N-body sims, the Las Damas Carmen and the Horizon Run, to calculate the bulk flows of various sized volumes in the simulation boxes. Once the bulk flow velocities ad a function of scale is found, investigate the mass and gravitational potential distribution around the volume. Find that matter densities can be asymmetrical and difficult to detect in real surveys, however, the gravitation potential and its gradient may provide better tolls to investigate the underlying matter distribution. This study shows that bulk flows are indeed potential flows and thus provides information on the flow sources. Also show that bulk flow magnitudes follow a Maxwellian distribution on scales >10 Mpc/h.
1512.09093
SN Refsdal: classification as a luminous and blue SN 1987A-like Type II supernova
Kelly, et al
HST and VLT NIR spectra and images of SN Refsdal, discovered as an Einstein cross in Fall 2014, show that the HST light curve of SN Refsdal matches the distinctive, slowly rising light curves of SN 1987A-like SNe, and find strong evidence for a broad H-alpha P-Cygni profile in the HST grism spectrum at z=1.49 of the spiral host galaxy. SNe IIn, powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H-alpha absorption. From the grism spectrum, measure an H-alpha expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame, provides additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V color and a high luminosity for the assumed range of potential magnifications. If SN Refsdal can be modeled as scaled version of SN 1987A, estimate it would have an eject mass of 20±5 Msun. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material (CSM). Using MOSFILRE and X-shoter spectra, estimate a sub solar host-galaxy metallicity (8.3±0.1 dex and <8.4 dex, respectively) near the explosion site.
Monday, December 28, 2015
Day 1030
Wednesday. Thursday. Christmas. Monday. Tuesday.
1512.07914
The LSST data management system
Juric, et al
LSST is a large-aperture, wide-field, ground-based sure system that will image the sky in 6 optical bands from 320 to 1050 nm, uniformly covering approximately 18k deg.sq. of the sky over 800 times. The LSST is currently under construction on Cerro Pachon in Chile, and expected to enter operations in 2022. Once operational, the LSST will explore a wide range of astrophysical questions, from discovering "killer" asteroids to examining the nature of DE. The LSST will generate on average 15 TB of data per night, and will require a comprehensive Data Management system to reduce the raw data to scientifically useful catalogs and images with minimum human intervention. These reductions will result in a real-time alert stream, and 11 data releases over the 10-year duration of LSST operations. To enable this processing, the LSST project is developing a new, general-purpose, high-performance, scalable, well documented, open source data processing software stack for O/IR surveys. Prototypes of this stack are already capable of processing data from existing cameras (e.g., SDSS, DECam, MegaCam), and form the basis of the HSC survey data reduction pipeline.
1512.07916
A free-form mass model of the Hubble Frontier Fields Cluster AS1063 (RXC J2248.l7-4431) with over one hundred constraints
Diego, Broadhurst, Wong, Silk, Lim, Zheng, Lam
Derive a free-form mass distribution for the massive cluster AS1063 (z=0.348) using the completed optical imaging from the HFF program. Based on a subset of 11 multiply lensed systems with spectroscopic redshift, produce a lens model that is accurate enough to unveil new multiply lensed systems, totally over a 100 arclets and to estimate their redshifts geometrically. Consistency is found between this precise model and that obtained using one the subset of lensed sources with spectroscopically measured redshifts. No significant offset is found between the centroid of the mass distribution and that of the X-ray emission map, suggesting a relatively relaxed state for this cluster, although a relatively large elongation of the mass distribution is apparent relative to the X-ray map. For the well resolved lensed images, provide detailed model comparisons to illustrate the precision of the model and hence the reliability of the de-lensed sources. A clear linear structure is associated with one such source extending 23 kpc in length, that could be an example f jet-induced star formation, at z=3.1.
1512.07914
The LSST data management system
Juric, et al
LSST is a large-aperture, wide-field, ground-based sure system that will image the sky in 6 optical bands from 320 to 1050 nm, uniformly covering approximately 18k deg.sq. of the sky over 800 times. The LSST is currently under construction on Cerro Pachon in Chile, and expected to enter operations in 2022. Once operational, the LSST will explore a wide range of astrophysical questions, from discovering "killer" asteroids to examining the nature of DE. The LSST will generate on average 15 TB of data per night, and will require a comprehensive Data Management system to reduce the raw data to scientifically useful catalogs and images with minimum human intervention. These reductions will result in a real-time alert stream, and 11 data releases over the 10-year duration of LSST operations. To enable this processing, the LSST project is developing a new, general-purpose, high-performance, scalable, well documented, open source data processing software stack for O/IR surveys. Prototypes of this stack are already capable of processing data from existing cameras (e.g., SDSS, DECam, MegaCam), and form the basis of the HSC survey data reduction pipeline.
1512.07916
A free-form mass model of the Hubble Frontier Fields Cluster AS1063 (RXC J2248.l7-4431) with over one hundred constraints
Diego, Broadhurst, Wong, Silk, Lim, Zheng, Lam
Derive a free-form mass distribution for the massive cluster AS1063 (z=0.348) using the completed optical imaging from the HFF program. Based on a subset of 11 multiply lensed systems with spectroscopic redshift, produce a lens model that is accurate enough to unveil new multiply lensed systems, totally over a 100 arclets and to estimate their redshifts geometrically. Consistency is found between this precise model and that obtained using one the subset of lensed sources with spectroscopically measured redshifts. No significant offset is found between the centroid of the mass distribution and that of the X-ray emission map, suggesting a relatively relaxed state for this cluster, although a relatively large elongation of the mass distribution is apparent relative to the X-ray map. For the well resolved lensed images, provide detailed model comparisons to illustrate the precision of the model and hence the reliability of the de-lensed sources. A clear linear structure is associated with one such source extending 23 kpc in length, that could be an example f jet-induced star formation, at z=3.1.
Tuesday, December 22, 2015
Day 1029
Tuesday.
1512.06268
Evolution of galaxy shapes from prolate to oblate through compaction events
Tomassetti, Dekel, et al
Study the evolution of global shapes of galaxies using cosmo sims. The shapes refer to the components of DM, stars and gas at the stellar half-mass radius. Most galaxies undergo a characteristic compaction event into a blue nugget at z~2-4, which marks the transition from a DM-dominated central body to a self-gravitating baryonic core. Find that in the high-z, DM-dominated phase, the stellar and DM systems tend to be triaxial, preferentially prolate and mutually aligned. The elongation is supported by an anisotropic velocity dispersion that originates form the assembly of the galaxy along a dominant large-scale filament. Estimate that torques by the dominant halo are capable of inducing the elongation of the stellar system and its alignment with the halo. Then, in association with the transition to self-gravity, small-pericenter orbits puff up and the DM and stellar systems evolve into a more spherical and oblate configuration, aligned with the gas disc and associated with rotation. This transition typically occurs when the stellar mass is ~1e9 Msun and the escape velocity in the core is ~100 km/s, indicating that SN feedback may be effective in keeping the core DM-dominated and the system prolate. The early elongated phase itself may be responsible for the compaction event, and the transition to the oblate phase may be associated with the subsequent quenching in the core.
1512.06507
Constraints on the identity of the dark matter from strong gravitational lenses
Li, Frenk, Cole, Gao, Bose, Hellwing
The CDM model unambiguously predicts that a large number of haloes should survive as sub haloes when they are accreted into a larger halo. The CDM model would be ruled out if such substructures were shown not to exist. By contrast, if the DM consists of WDM particles, then below a threshold mass that depends on the particle mass far fewer substructures would be present. Finding sub haloes below a certain mass would then rule out warm particle masses below some value. Strong gravitational lensing provides a clean method to measure the sub halo mass function through distortions in the structure of Einstein rings and giant arcs. Using mock lensing observations constructed from high-resolution N-body simulations, show that measurements of approximately 20 strong lens systems with a detection limit of 1e7 Msun/h would clearly distinguish CDM from WDM in the case where this consists of 7 keV sterile neutrinos such as those that might be responsible for the 3.5 keV X-ray emission line recently detected in galaxies and clusters.
1512.06268
Evolution of galaxy shapes from prolate to oblate through compaction events
Tomassetti, Dekel, et al
Study the evolution of global shapes of galaxies using cosmo sims. The shapes refer to the components of DM, stars and gas at the stellar half-mass radius. Most galaxies undergo a characteristic compaction event into a blue nugget at z~2-4, which marks the transition from a DM-dominated central body to a self-gravitating baryonic core. Find that in the high-z, DM-dominated phase, the stellar and DM systems tend to be triaxial, preferentially prolate and mutually aligned. The elongation is supported by an anisotropic velocity dispersion that originates form the assembly of the galaxy along a dominant large-scale filament. Estimate that torques by the dominant halo are capable of inducing the elongation of the stellar system and its alignment with the halo. Then, in association with the transition to self-gravity, small-pericenter orbits puff up and the DM and stellar systems evolve into a more spherical and oblate configuration, aligned with the gas disc and associated with rotation. This transition typically occurs when the stellar mass is ~1e9 Msun and the escape velocity in the core is ~100 km/s, indicating that SN feedback may be effective in keeping the core DM-dominated and the system prolate. The early elongated phase itself may be responsible for the compaction event, and the transition to the oblate phase may be associated with the subsequent quenching in the core.
1512.06507
Constraints on the identity of the dark matter from strong gravitational lenses
Li, Frenk, Cole, Gao, Bose, Hellwing
The CDM model unambiguously predicts that a large number of haloes should survive as sub haloes when they are accreted into a larger halo. The CDM model would be ruled out if such substructures were shown not to exist. By contrast, if the DM consists of WDM particles, then below a threshold mass that depends on the particle mass far fewer substructures would be present. Finding sub haloes below a certain mass would then rule out warm particle masses below some value. Strong gravitational lensing provides a clean method to measure the sub halo mass function through distortions in the structure of Einstein rings and giant arcs. Using mock lensing observations constructed from high-resolution N-body simulations, show that measurements of approximately 20 strong lens systems with a detection limit of 1e7 Msun/h would clearly distinguish CDM from WDM in the case where this consists of 7 keV sterile neutrinos such as those that might be responsible for the 3.5 keV X-ray emission line recently detected in galaxies and clusters.
Sunday, December 20, 2015
Day 1028
Monday.
1512.06084
Squeezing the halo bispectrum: a test of bias models
Dizgah, Chan, Norteña, Biagetti, Desjaques
Study the halo-matter cross bispectrum in the presence of primordial non-Gaussianity of the local type. Restrict to the squeezed limit, for which the calculation are straightforward, and perform the measurements in the initial conditions of N-body sims, to mitigate the contamination induced by nonlinear gravitational evolution. The halo-matter cross bispectrum is nto trivial even in this simple limit as it is strongly sensitive to the scale-dependence of the quadratic and 3rd-order halo bias. Therefore, it can be used to test biasing prescriptions. Consider 3 different prescription for halo clustering: excursion set peaks (ESP), local bias and a model in which the halo bias parameters are explicitly derived from a peak-background split. In all cases, the model parameters are fully constrained with statistics other than the cross bispectrum. Measure the cross bispectrum involving one halo fluctuation field and two mass overdensity fields for various halo masses and collapse redshifts. Find that the ESP is in reasonably good agreement with the numerical data, while the other alternatives considered fail in various cases. This suggests that the scale-dependent of halo bias also is a crucial ingredient to the squeezed limit of the halo bispectrum.
1512.06084
Squeezing the halo bispectrum: a test of bias models
Dizgah, Chan, Norteña, Biagetti, Desjaques
Study the halo-matter cross bispectrum in the presence of primordial non-Gaussianity of the local type. Restrict to the squeezed limit, for which the calculation are straightforward, and perform the measurements in the initial conditions of N-body sims, to mitigate the contamination induced by nonlinear gravitational evolution. The halo-matter cross bispectrum is nto trivial even in this simple limit as it is strongly sensitive to the scale-dependence of the quadratic and 3rd-order halo bias. Therefore, it can be used to test biasing prescriptions. Consider 3 different prescription for halo clustering: excursion set peaks (ESP), local bias and a model in which the halo bias parameters are explicitly derived from a peak-background split. In all cases, the model parameters are fully constrained with statistics other than the cross bispectrum. Measure the cross bispectrum involving one halo fluctuation field and two mass overdensity fields for various halo masses and collapse redshifts. Find that the ESP is in reasonably good agreement with the numerical data, while the other alternatives considered fail in various cases. This suggests that the scale-dependent of halo bias also is a crucial ingredient to the squeezed limit of the halo bispectrum.
Thursday, December 17, 2015
Day 1027
Friday.
1512.05591
Problems using ratios of galaxy shape moments on requirements for weak lensing surveys
Israel, Kitching, Massey
The shapes of galaxies can be quantified by ratios of their quadruple moments. For faint galaxies, observational noise can make the denominator close to zero, so the ratios become ill-defined. Knowledge of these ratios (i.e. their measured standard deviation) is commonly used to assess the efficiency of WL surveys. Since the requirements cannot be formally tested for faint galaxies, explore two complementary mitigation strategies. In many WL contexts, the most problematic sources can be removed by a cut in measured size. Investigate how a size cuts affects the required precision of the charge transfer inefficiency model and find slightly wider tolerance margins compared to the full size distribution. However, subtle cases in the data analysis chain may be introduced. Instead, as the second strategy, propose requirements directly on the quadrupole moments themselves. To optimally exploit a Stage-IV DE survey, find that the mean and standard deviation of a population of galaxies' quadrupole moments must be known to better than 1.4e-3 arcsec^2, or the Stokes parameters to 1.9e-3 arcsec^2. This testable requirements can now form the basis for future performance validation, or for proportioning the requirements between subsystems to ensure unbiased cosmo parameter inference.
1512.05734
SN Refsdal : Photometry and time delay measurements of the first Einstein Cross supernova
Rodney, et al
Present the first year HST imaging of SN Refsdal, a gravitationally lensed SN at z=1.488±0.001 with multiple images behind the galaxy cluster MACS J1149.6+2223. The first four observed images of SN Refsdal (images S1-S4) exhibited a slow rise (one ~150 days) to reach a broad peak brightness around 20 April 2015. Using a set of light curve template constructed from the family of SN 1987A-like peculiar Type II SNe, measure time delays for the 4 images relative to S1 of 4±4 (for S2), 2±5 (S3), and 24±7 days (S4). The measured magnification ratios relative to S1 are 1.15±0.05 (S2), 1.01±0.04 (S3), and 0.34±0.01 (S4). Find that none of the template light curves fully captures the photometric behavior of SN Refsdal, so also derive complementary measurements for these parameters using polynomials to represent the intrinsic light curve shape. These more flexible fits deliver fully consistent time delays of 7±2 days (S2), 0.6±3 days (S3), and 27±8 days (S4). The lensing magnification ratios are similarly consistent, measured as 1.17±0.02 (S2), 1.00±0.01 (S3), and 0.38±0.02 (S4). Compare these measurements against published predictions from lens models, and find that the majority of model predictions are in very good agreement with the measurements. Finally, discuss avenues for future improvement of time delay measurements -- both for SN Refsdal and for other strongly lensed SNe yet to come.
1512.05591
Problems using ratios of galaxy shape moments on requirements for weak lensing surveys
Israel, Kitching, Massey
The shapes of galaxies can be quantified by ratios of their quadruple moments. For faint galaxies, observational noise can make the denominator close to zero, so the ratios become ill-defined. Knowledge of these ratios (i.e. their measured standard deviation) is commonly used to assess the efficiency of WL surveys. Since the requirements cannot be formally tested for faint galaxies, explore two complementary mitigation strategies. In many WL contexts, the most problematic sources can be removed by a cut in measured size. Investigate how a size cuts affects the required precision of the charge transfer inefficiency model and find slightly wider tolerance margins compared to the full size distribution. However, subtle cases in the data analysis chain may be introduced. Instead, as the second strategy, propose requirements directly on the quadrupole moments themselves. To optimally exploit a Stage-IV DE survey, find that the mean and standard deviation of a population of galaxies' quadrupole moments must be known to better than 1.4e-3 arcsec^2, or the Stokes parameters to 1.9e-3 arcsec^2. This testable requirements can now form the basis for future performance validation, or for proportioning the requirements between subsystems to ensure unbiased cosmo parameter inference.
1512.05734
SN Refsdal : Photometry and time delay measurements of the first Einstein Cross supernova
Rodney, et al
Present the first year HST imaging of SN Refsdal, a gravitationally lensed SN at z=1.488±0.001 with multiple images behind the galaxy cluster MACS J1149.6+2223. The first four observed images of SN Refsdal (images S1-S4) exhibited a slow rise (one ~150 days) to reach a broad peak brightness around 20 April 2015. Using a set of light curve template constructed from the family of SN 1987A-like peculiar Type II SNe, measure time delays for the 4 images relative to S1 of 4±4 (for S2), 2±5 (S3), and 24±7 days (S4). The measured magnification ratios relative to S1 are 1.15±0.05 (S2), 1.01±0.04 (S3), and 0.34±0.01 (S4). Find that none of the template light curves fully captures the photometric behavior of SN Refsdal, so also derive complementary measurements for these parameters using polynomials to represent the intrinsic light curve shape. These more flexible fits deliver fully consistent time delays of 7±2 days (S2), 0.6±3 days (S3), and 27±8 days (S4). The lensing magnification ratios are similarly consistent, measured as 1.17±0.02 (S2), 1.00±0.01 (S3), and 0.38±0.02 (S4). Compare these measurements against published predictions from lens models, and find that the majority of model predictions are in very good agreement with the measurements. Finally, discuss avenues for future improvement of time delay measurements -- both for SN Refsdal and for other strongly lensed SNe yet to come.
Day 1026
Thursday.
Special Topics
Search for new physics in high mass diphoton events at ATLAS and CMS
CMS collaboration
Report on a search for new physics using high mass diphoton events. The search employs 2.6 fb^-1 of pp collision data collected by the CMS experiments in 2015 at sqrt(s)=13 TeV and it is principally aimed at extra dimensional models leading to resonant production of two photons. Limits on the production cross section of Randal-Sundrum graviton decaying to two photons are obtained in the range 500-4500 GeV.
1512.05095
Degeneracies of parametric lens model families near folds and cusps
Wagner, Bartelmann
Develop an approach to select families of lens models that can describe doubly and triply gravitationally lensed images near folds and cusps using the model-independent ratios of lensing-potential derivatives derived in Wagner & Bartelmann (2015). Models are selected by comparing these model-independent ratios of potential derivatives to (numerically determined) ratios of potential derivatives along critical curves for entire lens model families in a given range of parameter values. This comparison returns parameter ranges which lens model families can reproduce observation within, as well as sections of the critical curve where image sets of the observed type can appear. If the model-independent potential-derivative ratios inferred form the observation fall outside the range of these ratios derived for the lens model family, the entire family can be excluded as a feasible model in the given volume in parameter space. Employ this approach for the family of singular isothermal spheres with external shear to examples of lensing by a galaxy and two galaxy clusters (JVAS B1422+231, SDSS J222+2745,and MACS J1149.5+2223) and show that the results obtained by the general method are in good agreement with results of previous model fits.
1512.05198
Cosmology with all-sky surveys
Bilicki
Various aspects of cosmo require comprehensive all-sky mapping of the cosmic web to considerable depths. In order to probe the whole extragalactic sky beyond 100 Mpc, one must draw on multi wavelength datasets and state-of-the-art photometric z techniques. Summarize the dedicated program that employs the largest photometric all-sky surveys -- 2MASS, WISE and SuperCOSMOS -- to obtain accurate redshift estimates of millions of galaxies. The first outcome of these efforts -- the 2MASS Photometric Redshift Catalog (2MPZ) -- was publicly release in 2013 and includes almost 1 M galaxies with a median redshift of z~0.1. Discuss how the catalog was constructed and how it is being used for various cosmo tests. Also present how combining the WISE mid-IR survey with SuperCOSMOS optical data allows using to depths over 1Gpc on unprecedented angular scales. These photo-z samples, with about 20M sources in total, provide access to volumes large enough to sugary observationally the Copernican Principle of universal homogeneity and isotropy, as well as to probe various aspects of DE and DM through cross-correlations with other data such as the cosmic microwave or gamma-ray backgrounds. They constitute a test-bed for forthcoming wide-angle multi-million galaxy samples expected from such instruments as the SKA, Euclid or LSST.
Special Topics
Search for new physics in high mass diphoton events at ATLAS and CMS
CMS collaboration
Report on a search for new physics using high mass diphoton events. The search employs 2.6 fb^-1 of pp collision data collected by the CMS experiments in 2015 at sqrt(s)=13 TeV and it is principally aimed at extra dimensional models leading to resonant production of two photons. Limits on the production cross section of Randal-Sundrum graviton decaying to two photons are obtained in the range 500-4500 GeV.
1512.05095
Degeneracies of parametric lens model families near folds and cusps
Wagner, Bartelmann
Develop an approach to select families of lens models that can describe doubly and triply gravitationally lensed images near folds and cusps using the model-independent ratios of lensing-potential derivatives derived in Wagner & Bartelmann (2015). Models are selected by comparing these model-independent ratios of potential derivatives to (numerically determined) ratios of potential derivatives along critical curves for entire lens model families in a given range of parameter values. This comparison returns parameter ranges which lens model families can reproduce observation within, as well as sections of the critical curve where image sets of the observed type can appear. If the model-independent potential-derivative ratios inferred form the observation fall outside the range of these ratios derived for the lens model family, the entire family can be excluded as a feasible model in the given volume in parameter space. Employ this approach for the family of singular isothermal spheres with external shear to examples of lensing by a galaxy and two galaxy clusters (JVAS B1422+231, SDSS J222+2745,and MACS J1149.5+2223) and show that the results obtained by the general method are in good agreement with results of previous model fits.
1512.05198
Cosmology with all-sky surveys
Bilicki
Various aspects of cosmo require comprehensive all-sky mapping of the cosmic web to considerable depths. In order to probe the whole extragalactic sky beyond 100 Mpc, one must draw on multi wavelength datasets and state-of-the-art photometric z techniques. Summarize the dedicated program that employs the largest photometric all-sky surveys -- 2MASS, WISE and SuperCOSMOS -- to obtain accurate redshift estimates of millions of galaxies. The first outcome of these efforts -- the 2MASS Photometric Redshift Catalog (2MPZ) -- was publicly release in 2013 and includes almost 1 M galaxies with a median redshift of z~0.1. Discuss how the catalog was constructed and how it is being used for various cosmo tests. Also present how combining the WISE mid-IR survey with SuperCOSMOS optical data allows using to depths over 1Gpc on unprecedented angular scales. These photo-z samples, with about 20M sources in total, provide access to volumes large enough to sugary observationally the Copernican Principle of universal homogeneity and isotropy, as well as to probe various aspects of DE and DM through cross-correlations with other data such as the cosmic microwave or gamma-ray backgrounds. They constitute a test-bed for forthcoming wide-angle multi-million galaxy samples expected from such instruments as the SKA, Euclid or LSST.
Tuesday, December 15, 2015
Day 1025
Wednesday.
1512.03057
Exploring the SDSS Photometric galaxies with clustering redshifts
Rahman, Mendez, Ménard, Scranton, Schmidt, Morrison, Budavári
Apply clustering-based z inference to all extended source from SDSS photometric catalogue, down to r=22. Map the relationships between colors and redshift, without assumption of the sources' spectral energy distributions (SED). Identify and late SF, quiescent galaxies, and AGN, as well as color changes due to spectral features, such as the 4000 A break, redshirting through specific filters. The mapping is globally in good agreement with color-reshift tracks computed with SED templates, but reveals informative differences, such as the need for a lower fraction of M-type stars in certain templates. Compare the clustering-redshift estimates to photometric z and find those two independent estimators to be in good agreement at each limiting magnuide considered. Finally, present the global clustering-redshift distribution of Sloan extended sources, showing objects up to z~0.8. While the overall shape agrees with that inferred from photometric redshifts, the clustering redshift technique results in a smoother distribution, with no indication of structure in redshift space suggested by the photo-z estimates (likely artifacts imprinted by their spectra training set). Also infer a higher fraction of high-z objects. The mapping between the 4 observed colors and redshift can be used to estimate the z probability distribution function of individual galaxies. This work is an initial step towards producing a general mapping between redshift and all available observables in the photometric space, including brightness, size, concentration, and ellipticity.
1512.03814
The XXL Survey. XIII. Baryon content of the bright cluster sample
Eckert, et al
Traditionally, galaxy clusters have been expected to retain all the material accreted since their formation epoch. For this reason, their matter content should be representative of the Universe as a whole, and thus their baryon fraction should be close to the Universal baryon fraction. Make use of the sample of the 100 brightest galaxy clusters discovered in the XXL survey to investigate the fraction of baryons in the form of hot gas and stars in the cluster population. Measure the gas masses of the detected haloes and use a mass--temperature relation directly calibrated using WL measurements for a subset of XXL clusters to estimate the halo mass. Find that the WL calibrated gas fraction of XXL-100-GC clusters is substantially lower than was found n previous studies using hydrostatic masses. The best-fit relation between gas fraction and mass reads f_gas,500 = 0.055±0.007(M_500/1e14 Msun)^0.21±0.11. The baryon budget of galaxy clusters therefore falls short of the Universal baryon fraction by about a factor of two at r_500. The measurements require a hydrostatic bias 1-b=M_X/M_WL=0.72±0.08 to match the gas fraction obtained using lensing and hydrostatic equilibrium. Comparing the gas fraction measurements with the expectations from numerical simulations, the results favor an extreme feedback scheme in which a significant fraction of the baryons are expelled from the cores of halos. This model is, however, in contrast with the thermodynamical properties of observed haloes, which might suggest that WL masses are over estimated. Note that the mass bias 1-b=0.58 as required to reconcile Planck CMB and cluster counts should translate into an even lower baryon fraction, which poses a major challenge to the current understanding of galaxy clusters.
1512.04535
Cross-correlation of gravitational lensing from DES science verification data with SPT and Planck lensing
Kirk, et al
Measure the cross-correlation between WL of galaxy images and of the CMB. The effects of gravitational lensing on different sources will be correlated if the ending is caused by the same mass fluctuations. Use galaxy shape measurements from DES SV (139 deg sq) and overlapping CMB lensing from SPT and Planck. The DES source galaxies have a median redshift of z_med~0.7, while the CMB lensing kernel is broad and peaks at z~2. The resulting cross-correlationis maximally sensitive to mass fluctuations at z~0.44. Assuming the Planck 2015 best-fit cosmology, the amplitude of the DESXSPT cross-power is found to be A=0.88±0.30 and that from DESXPlanck to be A=0.86±0.39, where A=1 corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of 2.9sigma and 2.2sigma respectively. Demonstrate that the results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photometric z uncertainty and CMB lensing systematics. Significant IA of galaxy shapes would increase the X-corr signal inferred from the data; calculate a value of A=1.08±0.36 for DESXSPT when correcting the observations with a simple IA model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation, given the size of the statistical uncertainties and the significant impact of systematic errors, particularly IAs. Provide forecasts for the expected S/N of the combination of the 5-year DES survey and SPT-3G.
1512.04654
Deja Vu all over again: The reappearance of supernova Refsdal
Kelly, et al
In HST imaging taken on 10 Nov 2014, 4 images of SN 'Refsdal' (z=1.49) appeared in an Einstein-cross--like configuration (images S1-S4) around an early-type galaxy in the cluster MACS J1149.5+2223 (z=0.54). The gravitational potential of the cluster creates 3 full images of the SF host galaxy of the SN. Almost all lens models of the cluster have predicted that the SN should reappear within approximately one year in a second host-galaxy image, offset by ~8" from the previous images. In HST observations taken on 11 Dec 2015, find a new source that is interpreted as a new image of SN Refsdal. This marks the first time the appearance of a SN a a particular time and location in the sky was successfully predicted in advance! Use these data and the light curve from the first 4 observed images of SN Refsdal to place constraints on the relative time delay and magnification of the new image (SX), compare to images S1-S4. This enables, for the first time, to test lens model predictions of both magnifications and time delays for a lensed SN. Find that the timing and brightness of the new image are consistent with the blind predictions of a fraction of the models. The reappearance illustrate the discriminatory power of this blind test and its utility to uncover sources of systematic uncertainty in the lens models. From planned HST photometry, expect to reach precision of 1-2% on the relative time delay between S1-S4 and SX.
1512.03057
Exploring the SDSS Photometric galaxies with clustering redshifts
Rahman, Mendez, Ménard, Scranton, Schmidt, Morrison, Budavári
Apply clustering-based z inference to all extended source from SDSS photometric catalogue, down to r=22. Map the relationships between colors and redshift, without assumption of the sources' spectral energy distributions (SED). Identify and late SF, quiescent galaxies, and AGN, as well as color changes due to spectral features, such as the 4000 A break, redshirting through specific filters. The mapping is globally in good agreement with color-reshift tracks computed with SED templates, but reveals informative differences, such as the need for a lower fraction of M-type stars in certain templates. Compare the clustering-redshift estimates to photometric z and find those two independent estimators to be in good agreement at each limiting magnuide considered. Finally, present the global clustering-redshift distribution of Sloan extended sources, showing objects up to z~0.8. While the overall shape agrees with that inferred from photometric redshifts, the clustering redshift technique results in a smoother distribution, with no indication of structure in redshift space suggested by the photo-z estimates (likely artifacts imprinted by their spectra training set). Also infer a higher fraction of high-z objects. The mapping between the 4 observed colors and redshift can be used to estimate the z probability distribution function of individual galaxies. This work is an initial step towards producing a general mapping between redshift and all available observables in the photometric space, including brightness, size, concentration, and ellipticity.
1512.03814
The XXL Survey. XIII. Baryon content of the bright cluster sample
Eckert, et al
Traditionally, galaxy clusters have been expected to retain all the material accreted since their formation epoch. For this reason, their matter content should be representative of the Universe as a whole, and thus their baryon fraction should be close to the Universal baryon fraction. Make use of the sample of the 100 brightest galaxy clusters discovered in the XXL survey to investigate the fraction of baryons in the form of hot gas and stars in the cluster population. Measure the gas masses of the detected haloes and use a mass--temperature relation directly calibrated using WL measurements for a subset of XXL clusters to estimate the halo mass. Find that the WL calibrated gas fraction of XXL-100-GC clusters is substantially lower than was found n previous studies using hydrostatic masses. The best-fit relation between gas fraction and mass reads f_gas,500 = 0.055±0.007(M_500/1e14 Msun)^0.21±0.11. The baryon budget of galaxy clusters therefore falls short of the Universal baryon fraction by about a factor of two at r_500. The measurements require a hydrostatic bias 1-b=M_X/M_WL=0.72±0.08 to match the gas fraction obtained using lensing and hydrostatic equilibrium. Comparing the gas fraction measurements with the expectations from numerical simulations, the results favor an extreme feedback scheme in which a significant fraction of the baryons are expelled from the cores of halos. This model is, however, in contrast with the thermodynamical properties of observed haloes, which might suggest that WL masses are over estimated. Note that the mass bias 1-b=0.58 as required to reconcile Planck CMB and cluster counts should translate into an even lower baryon fraction, which poses a major challenge to the current understanding of galaxy clusters.
1512.04535
Cross-correlation of gravitational lensing from DES science verification data with SPT and Planck lensing
Kirk, et al
Measure the cross-correlation between WL of galaxy images and of the CMB. The effects of gravitational lensing on different sources will be correlated if the ending is caused by the same mass fluctuations. Use galaxy shape measurements from DES SV (139 deg sq) and overlapping CMB lensing from SPT and Planck. The DES source galaxies have a median redshift of z_med~0.7, while the CMB lensing kernel is broad and peaks at z~2. The resulting cross-correlationis maximally sensitive to mass fluctuations at z~0.44. Assuming the Planck 2015 best-fit cosmology, the amplitude of the DESXSPT cross-power is found to be A=0.88±0.30 and that from DESXPlanck to be A=0.86±0.39, where A=1 corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of 2.9sigma and 2.2sigma respectively. Demonstrate that the results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photometric z uncertainty and CMB lensing systematics. Significant IA of galaxy shapes would increase the X-corr signal inferred from the data; calculate a value of A=1.08±0.36 for DESXSPT when correcting the observations with a simple IA model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation, given the size of the statistical uncertainties and the significant impact of systematic errors, particularly IAs. Provide forecasts for the expected S/N of the combination of the 5-year DES survey and SPT-3G.
1512.04654
Deja Vu all over again: The reappearance of supernova Refsdal
Kelly, et al
In HST imaging taken on 10 Nov 2014, 4 images of SN 'Refsdal' (z=1.49) appeared in an Einstein-cross--like configuration (images S1-S4) around an early-type galaxy in the cluster MACS J1149.5+2223 (z=0.54). The gravitational potential of the cluster creates 3 full images of the SF host galaxy of the SN. Almost all lens models of the cluster have predicted that the SN should reappear within approximately one year in a second host-galaxy image, offset by ~8" from the previous images. In HST observations taken on 11 Dec 2015, find a new source that is interpreted as a new image of SN Refsdal. This marks the first time the appearance of a SN a a particular time and location in the sky was successfully predicted in advance! Use these data and the light curve from the first 4 observed images of SN Refsdal to place constraints on the relative time delay and magnification of the new image (SX), compare to images S1-S4. This enables, for the first time, to test lens model predictions of both magnifications and time delays for a lensed SN. Find that the timing and brightness of the new image are consistent with the blind predictions of a fraction of the models. The reappearance illustrate the discriminatory power of this blind test and its utility to uncover sources of systematic uncertainty in the lens models. From planned HST photometry, expect to reach precision of 1-2% on the relative time delay between S1-S4 and SX.
Monday, December 14, 2015
Day 1024
Tuesday.
Special Topics
Detection of a SN near the center of the galaxy cluster field MACS1149 consistent wth predictions of a new image of Supernova Refsdal
www.astronomerstelegram.org
In HST WFC3-IR exposures taken on UT 2015 Dec 10 (GO-14199; PI:Kelly), a new transient source in the MACS J1149.6+2223 (Ebeling+2003) galaxy cluster field has been discovered.
The new source was not detected in WFC3-IR exposures taken during a previous visit to the field on UT 2015 Oct 30.8 nor in earlier imaging from the Frontier SN program, Frontier fields, or Grism Lens-Amplified Survey from Space (GLASS) programs.
The new image is marginally detected in data taken in November 2015. This new image coincides with a multiply imaged BG galaxy at z-1.49. This same galaxy, but seen as a different image, is the host galaxy of SN Refsdal, a SN discovered in November 2014 as four separate images in an Einstein cross configuraiont round an early-type cluster member. Multiple lensing models consistently predicted that SN Refsdal would re-appear, within several years, at the position of the other image of the host galaxy cluster to the galaxy center. The new SN, denoted 'SX', is significantly fainter than images S1-S3 of the SN Refsdal Einstein cross when they were discovered in images taken on UT 2014 November 10.
The new SN position is both approximately spatially and temporally coincident with predictions for the location and timing of the delayed image of SN Refsdal. Moreover, the brightness differences are also approximately consistent with relative magnification predictions.
Conclude that this new SN is likely the re-appearance of SN Refsdal.
1512.03834
Are the formation and abundances of metal-poor stars the result of dust dynamics?
Hopkins, Conroy
Large dust grains can fluctuate dramatically in their local density, relative to gas, in neutral, turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. Show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains under these conditions. This can have important consequences for star formation and stellar abundances in extremely metal-poor stars. Low-mass stars could form in dust-enhanced regions almost immediately after some dust forms, even if the galaxy-average metallicity is too low for fragmentation to occur. The abundances of these 'promoted' stars may contain interesting signatures, as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced or fluctuate independently. Remarkably, otherwise puzzling abundance patterns of some metal poor stars can be well-fit by standard core-collapse SNe yeilds, if fluctuating dust-to-gas ratios are allowed. Also show that the observed log-normal-like distribution of enhancements n these species agrees with the simulations. Moreover, confirm Mg and Si are correlated in these stars, with abundance ratios similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows large enhancements as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. This suggests that (1) dust exists in second-generation star formation, (2) dust-to-gas ratio fluctuations occurs and can be important for star formation, and (3) light element abundances of these stars may be affected by the chemistry of dust where they formed, rather than directly tracing nucleosynthesis.
1512.03903
The XXL Survey X: K-band luminosity - weak-lensing mass relation for groups and clusters of galaxies
Ziparo, Smith, et al
Present the K-band luminosity-halomass relation (L_K,500-M_500,WL), for a subsample of 20 of the 100 brightest clusters in the XXL survey observed with WIRCam at CFHT. Measure this relation via WL down to M_500,WL=3.5e13 Msun, allowing to investigate whether the slope of the L_K-M relation is different for groups and clusters, as seen in other works. The clusters in the sample span a wide range in mass, M=0.35-12.1e14 Msun, at 0<z<0.6. The K-band luminosity scales as log10(L_K,500/1e12 Lsun) ~ beta log10 (M_500,WL/1e14 Msun) with beta = 0.85±0.3 and an intrinsic scatter of sigma_lnL_K|M = 0.37±0.18. combining the sample with some clusters in LoCuSS, obtain a slope of 1.05±0.15 and an intrinsic scatter of 0.14±0.08. The flattening in the L_K-M seen in previous works is not seen here and might be a result of a bias in the mass measurement due to assumptions on the dynamical state of the systems. Also study the richness-mass relation and find that group-sized halos have more galaxies per unit halo mass than massive clusters. However, the BCG in low-mass systems contributes a greater fraction to the total cluster light than BCGs do in massive clusters; the luminosity gap between the two brightest galaxies is more prominent for group-sized haloes. This result is a natural outcome of the hierarchical growth of structures, where massive galaxies form and gain mass within low-mass groups and are ultimately accreted into more massive clusters to become either part of the BCG or one of the brighter galaxies.
1512.04189
Intensity mapping cross-correlations: connecting the largest scales to galaxy evolution
Wolf, Tonini, Blake, Wyithe
Intensity mapping of HI is a new observational tool that can be used to efficiently map the LSS of the Universe over wide redshift ranges. The PS of the intensity maps contains cosmo info on the matter distribution and probes galaxy evolution by tracing the HI content of galaxies at different redshifts and the scale-dependence of HI clustering. The cross-correlation of intensity maps with galaxy surveys is a robust measure of the PS which diminishes systematics caused by instrumental effects and foreground removal. Examine the cross-correlation signatures at z=0.9 using a variant of the semi-analytical galaxy formation model SAGE apply to the Millennium sim in order to model the HI gas of galaxies as well as their optical magnitudes based on their SF history. Determine the clustering of the cross-correlation power for different type of galaxies determined by their colors, acting as a proxy for their SF activity. Find that the cross-correlation coefficient for red quiescent galaxies falls off more quickly on smaller scales k>0.2h/Mpc than for blue SF galaxies. Additionally, create a mock catalogue of highly SF galaxies using a select function to mimic the WiggleZ survey, and use this to predict existing and future cross-correlation measurement of the GBT and Parkes telescope. Find that the cross-power of highly SF galaxies shows a higher clustering on small scales than any other galaxy type and that this significantly alters the PS shape on sales k>0.2h/Mpc. Show that the cross-correlation coefficient is not negligible when interpreting the cosmo cross-power spectrum. On the other hand, it contains information about the HI content of the optically selected galaxies.
Special Topics
Detection of a SN near the center of the galaxy cluster field MACS1149 consistent wth predictions of a new image of Supernova Refsdal
www.astronomerstelegram.org
In HST WFC3-IR exposures taken on UT 2015 Dec 10 (GO-14199; PI:Kelly), a new transient source in the MACS J1149.6+2223 (Ebeling+2003) galaxy cluster field has been discovered.
The new source was not detected in WFC3-IR exposures taken during a previous visit to the field on UT 2015 Oct 30.8 nor in earlier imaging from the Frontier SN program, Frontier fields, or Grism Lens-Amplified Survey from Space (GLASS) programs.
The new image is marginally detected in data taken in November 2015. This new image coincides with a multiply imaged BG galaxy at z-1.49. This same galaxy, but seen as a different image, is the host galaxy of SN Refsdal, a SN discovered in November 2014 as four separate images in an Einstein cross configuraiont round an early-type cluster member. Multiple lensing models consistently predicted that SN Refsdal would re-appear, within several years, at the position of the other image of the host galaxy cluster to the galaxy center. The new SN, denoted 'SX', is significantly fainter than images S1-S3 of the SN Refsdal Einstein cross when they were discovered in images taken on UT 2014 November 10.
The new SN position is both approximately spatially and temporally coincident with predictions for the location and timing of the delayed image of SN Refsdal. Moreover, the brightness differences are also approximately consistent with relative magnification predictions.
Conclude that this new SN is likely the re-appearance of SN Refsdal.
1512.03834
Are the formation and abundances of metal-poor stars the result of dust dynamics?
Hopkins, Conroy
Large dust grains can fluctuate dramatically in their local density, relative to gas, in neutral, turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. Show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains under these conditions. This can have important consequences for star formation and stellar abundances in extremely metal-poor stars. Low-mass stars could form in dust-enhanced regions almost immediately after some dust forms, even if the galaxy-average metallicity is too low for fragmentation to occur. The abundances of these 'promoted' stars may contain interesting signatures, as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced or fluctuate independently. Remarkably, otherwise puzzling abundance patterns of some metal poor stars can be well-fit by standard core-collapse SNe yeilds, if fluctuating dust-to-gas ratios are allowed. Also show that the observed log-normal-like distribution of enhancements n these species agrees with the simulations. Moreover, confirm Mg and Si are correlated in these stars, with abundance ratios similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows large enhancements as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. This suggests that (1) dust exists in second-generation star formation, (2) dust-to-gas ratio fluctuations occurs and can be important for star formation, and (3) light element abundances of these stars may be affected by the chemistry of dust where they formed, rather than directly tracing nucleosynthesis.
1512.03903
The XXL Survey X: K-band luminosity - weak-lensing mass relation for groups and clusters of galaxies
Ziparo, Smith, et al
Present the K-band luminosity-halomass relation (L_K,500-M_500,WL), for a subsample of 20 of the 100 brightest clusters in the XXL survey observed with WIRCam at CFHT. Measure this relation via WL down to M_500,WL=3.5e13 Msun, allowing to investigate whether the slope of the L_K-M relation is different for groups and clusters, as seen in other works. The clusters in the sample span a wide range in mass, M=0.35-12.1e14 Msun, at 0<z<0.6. The K-band luminosity scales as log10(L_K,500/1e12 Lsun) ~ beta log10 (M_500,WL/1e14 Msun) with beta = 0.85±0.3 and an intrinsic scatter of sigma_lnL_K|M = 0.37±0.18. combining the sample with some clusters in LoCuSS, obtain a slope of 1.05±0.15 and an intrinsic scatter of 0.14±0.08. The flattening in the L_K-M seen in previous works is not seen here and might be a result of a bias in the mass measurement due to assumptions on the dynamical state of the systems. Also study the richness-mass relation and find that group-sized halos have more galaxies per unit halo mass than massive clusters. However, the BCG in low-mass systems contributes a greater fraction to the total cluster light than BCGs do in massive clusters; the luminosity gap between the two brightest galaxies is more prominent for group-sized haloes. This result is a natural outcome of the hierarchical growth of structures, where massive galaxies form and gain mass within low-mass groups and are ultimately accreted into more massive clusters to become either part of the BCG or one of the brighter galaxies.
1512.04189
Intensity mapping cross-correlations: connecting the largest scales to galaxy evolution
Wolf, Tonini, Blake, Wyithe
Intensity mapping of HI is a new observational tool that can be used to efficiently map the LSS of the Universe over wide redshift ranges. The PS of the intensity maps contains cosmo info on the matter distribution and probes galaxy evolution by tracing the HI content of galaxies at different redshifts and the scale-dependence of HI clustering. The cross-correlation of intensity maps with galaxy surveys is a robust measure of the PS which diminishes systematics caused by instrumental effects and foreground removal. Examine the cross-correlation signatures at z=0.9 using a variant of the semi-analytical galaxy formation model SAGE apply to the Millennium sim in order to model the HI gas of galaxies as well as their optical magnitudes based on their SF history. Determine the clustering of the cross-correlation power for different type of galaxies determined by their colors, acting as a proxy for their SF activity. Find that the cross-correlation coefficient for red quiescent galaxies falls off more quickly on smaller scales k>0.2h/Mpc than for blue SF galaxies. Additionally, create a mock catalogue of highly SF galaxies using a select function to mimic the WiggleZ survey, and use this to predict existing and future cross-correlation measurement of the GBT and Parkes telescope. Find that the cross-power of highly SF galaxies shows a higher clustering on small scales than any other galaxy type and that this significantly alters the PS shape on sales k>0.2h/Mpc. Show that the cross-correlation coefficient is not negligible when interpreting the cosmo cross-power spectrum. On the other hand, it contains information about the HI content of the optically selected galaxies.
Sunday, December 13, 2015
Day 1023
Monday.
1512.03538
The inner structure of dwarf sized haloes in warm and cold dark matter cosmologies
Gonzalez-Samaniego, Avila-Reese, Colin
By means of N-body+hydro zoom-in sims, study the evolution of the inner DM and stellar mass distributions of central dwarf galaxies formed in haloes of viral masses 2-3e10 Msun at z=0, both in a WDM and CDM cosmology. The half-mode mass in the WDM power spectrum of the simulations is Mv=2e10 Msun. In the DM only sims halo density profiles are well described by the NFW parametric fit in both cosmologies, though the WDM haloes have concentrations lower by factors 1.5-2.0 than their CDM counterparts. In the hydro sims, the effects of baryons significantly flatten the inner density, velocity dispersion, and pseudo phase-space density profiles of the WDM haloes but not of the CDM ones. The density slope measured at ~0.02xRv, alpha, becomes shallow in periods of 2 to 5 Gyr in the WDM runs. Explore whether this flattening process correlates with the global SF, Ms/Mv ratio, gas outflow, and internal specific angular momentum histories. Do not find any clear trends but when alpha is shallower than -0.5, Ms/Mv is always between 0.25 and 1%. Conclude that the main reason of the formation of the shallow core is the presence of strong gas mass fluctuations inside the inner halo, which are consequence of the feedback driven by a very bursty and sustained SF history in shallow gravitational potentials. The WDM halos, which ensemble late and are less concentrated than the CDM ones, obey these conditions. There are also (rare) CDM systems with extend mass assembly histories that obey these conditions and form indeed shallow cores. The dynamical heating and expansion processes, behind the DM core flattening, apply also to the stars in such a way that the stellar age and metallicity gradients of the dwarfs are softened, their stellar half-mass radii strongly grow with time, and their central surface densities decrease.
1512.03625
RCSLenS: A new estimator for large-scale galaxy-matter correlations
Buddendiek, et al
Measurements of galaxy bias b and galaxy-matter cross-correlation coefficient r for the BOSS LOWZ LRG sample. Using a statistical WL analysis of the RCSLenS, find the bias properties of this sample to be higher than previously reported with b=2.45 and r=1.64 on scales between 3' and 20'. Repeat the measurement for angular scales of 20'<theta<70' , which yields b=2.39 and r=1.24. This is the first application of a data compression analysis using a complete set of discrete estimators for gg lensing and galaxy clustering. As cosmo data sets grow, this new method of data compression will become increasingly important in order to interpret joint WL and galaxy clustering measurements and to estimate the data covariance. In future studies this formalism can be used as a tool to study the LSS of the universe to yield a precise determination of cosmo parameters.
1512.03626
CFHTLenS and RCSLenS: Testing photometric redshift distributions using angular cross-correlations with spectroscopic galaxy surveys
Choi et al
Determine the accuracy of galaxy redshift distributions as estimated from photo-z probability distributions p(z). The method utilizes measurements of the angular cross-correlation between photometric galaxies and an overlapping sample of galaxies with spectroscopic redshifts. Describe the redshift leakage from a galaxy photometric redshift bin j into a spectroscopic redshift bin i using the sum of the p(z) for the galaxies residing in bin j. Then predict the angular cross-correlation between photo and spectra galaxies due to intrinsic galaxy clustering when i!=j as a function of the measured angular cross-correlation when i=j. Also account for enhanced clustering arising from lensing magnification using a halo model. The comparison of this prediction with the measured signal provides a consistency check on the validity of using the summed p(z) to determine galaxy redshift distributions in cosmo analyses, as advocated by CFHTLenS. Present an analysis of the photo-z measured by CFHTLenS, which overlaps BOSS. Also analyse RCSLenS, which overlaps both BOSS and WiggleZ Dark Energy Survey. Find that the summed p(z) from both surveys are generally biased with respect to the true underlying distributions. If uncounted for, this bias would lead to errors in cosmo parameter estimation from CFHTLenS by less than ~4%. For photo-z bins which spatially overlap in 3-D with the spec-z sample, determine redshift bias corrections which can be used in future cosmo analyses that rely on accurate galaxy redshift distributions.
1512.03627
RCSLenS: Cosmic distances from weak lensing
Kitching, et al
Present results of applying the shear-ratio methods to the RCSLenS data. The method takes the ratio of the mean of the WL tangential shear signal about galaxy clusters, averaged over all clusters of the same redshift, in multiple background redshift inns. In taking a ratio the mass-dependence of the shear signal is cancelled-out leaving a statistic that is dependent on the geometric part of the lensing kernel only. Apply this method to 535 clusters and measure a cocmo-indpendent distance-redshift relation to redshifts z~1. In combination with Planck data, the method lifts the degeneracies in the CMB measurements, resulting in cosmo parameter constraints of OmegaM=0.31±0.10 and w0=-1.02±0.37, for a flat wCDM cosmology.
1512.03538
The inner structure of dwarf sized haloes in warm and cold dark matter cosmologies
Gonzalez-Samaniego, Avila-Reese, Colin
By means of N-body+hydro zoom-in sims, study the evolution of the inner DM and stellar mass distributions of central dwarf galaxies formed in haloes of viral masses 2-3e10 Msun at z=0, both in a WDM and CDM cosmology. The half-mode mass in the WDM power spectrum of the simulations is Mv=2e10 Msun. In the DM only sims halo density profiles are well described by the NFW parametric fit in both cosmologies, though the WDM haloes have concentrations lower by factors 1.5-2.0 than their CDM counterparts. In the hydro sims, the effects of baryons significantly flatten the inner density, velocity dispersion, and pseudo phase-space density profiles of the WDM haloes but not of the CDM ones. The density slope measured at ~0.02xRv, alpha, becomes shallow in periods of 2 to 5 Gyr in the WDM runs. Explore whether this flattening process correlates with the global SF, Ms/Mv ratio, gas outflow, and internal specific angular momentum histories. Do not find any clear trends but when alpha is shallower than -0.5, Ms/Mv is always between 0.25 and 1%. Conclude that the main reason of the formation of the shallow core is the presence of strong gas mass fluctuations inside the inner halo, which are consequence of the feedback driven by a very bursty and sustained SF history in shallow gravitational potentials. The WDM halos, which ensemble late and are less concentrated than the CDM ones, obey these conditions. There are also (rare) CDM systems with extend mass assembly histories that obey these conditions and form indeed shallow cores. The dynamical heating and expansion processes, behind the DM core flattening, apply also to the stars in such a way that the stellar age and metallicity gradients of the dwarfs are softened, their stellar half-mass radii strongly grow with time, and their central surface densities decrease.
1512.03625
RCSLenS: A new estimator for large-scale galaxy-matter correlations
Buddendiek, et al
Measurements of galaxy bias b and galaxy-matter cross-correlation coefficient r for the BOSS LOWZ LRG sample. Using a statistical WL analysis of the RCSLenS, find the bias properties of this sample to be higher than previously reported with b=2.45 and r=1.64 on scales between 3' and 20'. Repeat the measurement for angular scales of 20'<theta<70' , which yields b=2.39 and r=1.24. This is the first application of a data compression analysis using a complete set of discrete estimators for gg lensing and galaxy clustering. As cosmo data sets grow, this new method of data compression will become increasingly important in order to interpret joint WL and galaxy clustering measurements and to estimate the data covariance. In future studies this formalism can be used as a tool to study the LSS of the universe to yield a precise determination of cosmo parameters.
1512.03626
CFHTLenS and RCSLenS: Testing photometric redshift distributions using angular cross-correlations with spectroscopic galaxy surveys
Choi et al
Determine the accuracy of galaxy redshift distributions as estimated from photo-z probability distributions p(z). The method utilizes measurements of the angular cross-correlation between photometric galaxies and an overlapping sample of galaxies with spectroscopic redshifts. Describe the redshift leakage from a galaxy photometric redshift bin j into a spectroscopic redshift bin i using the sum of the p(z) for the galaxies residing in bin j. Then predict the angular cross-correlation between photo and spectra galaxies due to intrinsic galaxy clustering when i!=j as a function of the measured angular cross-correlation when i=j. Also account for enhanced clustering arising from lensing magnification using a halo model. The comparison of this prediction with the measured signal provides a consistency check on the validity of using the summed p(z) to determine galaxy redshift distributions in cosmo analyses, as advocated by CFHTLenS. Present an analysis of the photo-z measured by CFHTLenS, which overlaps BOSS. Also analyse RCSLenS, which overlaps both BOSS and WiggleZ Dark Energy Survey. Find that the summed p(z) from both surveys are generally biased with respect to the true underlying distributions. If uncounted for, this bias would lead to errors in cosmo parameter estimation from CFHTLenS by less than ~4%. For photo-z bins which spatially overlap in 3-D with the spec-z sample, determine redshift bias corrections which can be used in future cosmo analyses that rely on accurate galaxy redshift distributions.
1512.03627
RCSLenS: Cosmic distances from weak lensing
Kitching, et al
Present results of applying the shear-ratio methods to the RCSLenS data. The method takes the ratio of the mean of the WL tangential shear signal about galaxy clusters, averaged over all clusters of the same redshift, in multiple background redshift inns. In taking a ratio the mass-dependence of the shear signal is cancelled-out leaving a statistic that is dependent on the geometric part of the lensing kernel only. Apply this method to 535 clusters and measure a cocmo-indpendent distance-redshift relation to redshifts z~1. In combination with Planck data, the method lifts the degeneracies in the CMB measurements, resulting in cosmo parameter constraints of OmegaM=0.31±0.10 and w0=-1.02±0.37, for a flat wCDM cosmology.
Friday, December 11, 2015
Day 1022
Friday.
1512.03050
Introducing decorated HODs: modeling assembly bias in the galaxy-halo connection
Hearing, Zentner, van den Bosch, Campbell, Tollerud
The connection between galaxies and dark matter haloes is often inferred form data using probabilistic models, such as the Halo Occupation Distribution (HOD). Conventional HOD formulations assume that only halo mass governs the galaxy-halo connection. Violations of this assumption, known as galaxy assembly bias, threaten the HOD program. Introduce decorated HODs, a new, flexible class of models designed to account for assembly bias. Decorated HODs minimally expand the parameter space and maximize the independence between traditional and novel HOD parameters. Use decorated HODs to quality the influence of assembly bias on clustering and lensing statistics. For SDSS-like samples, the impact of assembly bias on galaxy clustering can be as large as a factor of two on r~200 kpc scales and ~15% in the linear regime. Assembly bias can either enhance or diminish clustering on large scales, but generally increases clustering on scales r<~1 Mpc. Performed the calculations with Halotools, an open-source, community-driven python package for studying the galaxy-halo connection. Conclude by describing the use of decorated HODs to treat assembly bias in otherwise conventional likelihood analyses.
1512.03062
Observation and confirmation of six strong lensing systems in the Dark Energy Survey Science Verification Data
Nord et al
In DES SV, identify 53 candidate systems, the obtain spectroscopic follow-up of 21 candidates using GMOS at Gemini South and IMACS at Magellan/Baade. Confirmed 6 candidates as gravitational lenses: Three of the systems are newly discovered, and the remaining three were previously known. Of the 21 observed candidates, the remaining 15 were either not detected in spectra observations, were observed and did not exhibit continuum emission (or spectral features), or were ruled out as lensing system. The confirmed sample consists of one group-scale and five galaxy cluster-scale lenses. The lensed sources range in redshift z~0.80-3.2, and in i-band surface brightness i_SB~23-25 mag/sq-arcsec (2" aperture) . For each of the 6 systems, estimate the Einstein rides and the enclosed mass, which have ranges ~5.0-8.6" and ~7.5e12-6.4e13 Msun, respectively.
1512.03402
Recovering the tidal field in the projected galaxy distribution
Alonso, Hadzhiyska, Strauss
Present a method to recover and study the projected gravitational tidal forces from a galaxy survey containing little or no redshift information. The method and the physical interpretation of the recovered tidal maps as a tracer of the cosmic web are described in detail. First apply the method to a simulated galaxy survey and study the accuracy with which the cosmic web can be recovered in the presence of different observational effects, showing that the projected tidal field can be estimated with reasonable precision over large regions of the sky. Then apply the method to the 2MASS survey and present a publicly available full-sky map of the projected tidal forces in the local Universe. As an example of an application of these data, further study the distribution of galaxy luminosities across the different elements of the cosmic web, finding that, while more luminous objects are found preferentially in the most dense environments, there is no further segregation by tidal environment.
1512.03050
Introducing decorated HODs: modeling assembly bias in the galaxy-halo connection
Hearing, Zentner, van den Bosch, Campbell, Tollerud
The connection between galaxies and dark matter haloes is often inferred form data using probabilistic models, such as the Halo Occupation Distribution (HOD). Conventional HOD formulations assume that only halo mass governs the galaxy-halo connection. Violations of this assumption, known as galaxy assembly bias, threaten the HOD program. Introduce decorated HODs, a new, flexible class of models designed to account for assembly bias. Decorated HODs minimally expand the parameter space and maximize the independence between traditional and novel HOD parameters. Use decorated HODs to quality the influence of assembly bias on clustering and lensing statistics. For SDSS-like samples, the impact of assembly bias on galaxy clustering can be as large as a factor of two on r~200 kpc scales and ~15% in the linear regime. Assembly bias can either enhance or diminish clustering on large scales, but generally increases clustering on scales r<~1 Mpc. Performed the calculations with Halotools, an open-source, community-driven python package for studying the galaxy-halo connection. Conclude by describing the use of decorated HODs to treat assembly bias in otherwise conventional likelihood analyses.
1512.03062
Observation and confirmation of six strong lensing systems in the Dark Energy Survey Science Verification Data
Nord et al
In DES SV, identify 53 candidate systems, the obtain spectroscopic follow-up of 21 candidates using GMOS at Gemini South and IMACS at Magellan/Baade. Confirmed 6 candidates as gravitational lenses: Three of the systems are newly discovered, and the remaining three were previously known. Of the 21 observed candidates, the remaining 15 were either not detected in spectra observations, were observed and did not exhibit continuum emission (or spectral features), or were ruled out as lensing system. The confirmed sample consists of one group-scale and five galaxy cluster-scale lenses. The lensed sources range in redshift z~0.80-3.2, and in i-band surface brightness i_SB~23-25 mag/sq-arcsec (2" aperture) . For each of the 6 systems, estimate the Einstein rides and the enclosed mass, which have ranges ~5.0-8.6" and ~7.5e12-6.4e13 Msun, respectively.
1512.03402
Recovering the tidal field in the projected galaxy distribution
Alonso, Hadzhiyska, Strauss
Present a method to recover and study the projected gravitational tidal forces from a galaxy survey containing little or no redshift information. The method and the physical interpretation of the recovered tidal maps as a tracer of the cosmic web are described in detail. First apply the method to a simulated galaxy survey and study the accuracy with which the cosmic web can be recovered in the presence of different observational effects, showing that the projected tidal field can be estimated with reasonable precision over large regions of the sky. Then apply the method to the 2MASS survey and present a publicly available full-sky map of the projected tidal forces in the local Universe. As an example of an application of these data, further study the distribution of galaxy luminosities across the different elements of the cosmic web, finding that, while more luminous objects are found preferentially in the most dense environments, there is no further segregation by tidal environment.
Wednesday, December 9, 2015
Day 1021
Thursday.
1512.02231
The large-scale 3-point correlation function of the SDSS BOSS DR12 CMASS galaxies
Slepian, Eisenstein, et al
Report a measurement of the large-scale 3PCF of galaxies using the largest dataset for this purpose to date; 777k LRGs in SDSS BOSS DR12 CMASS sample. This work exploits the novel algorithm of Slepian&Eisenstein (2015) to compute the multiple moments of the 3PCF in O(N^2) time, with N the number of galaxies. Leading-order perturbation theory models the data well in a compressed basis where one triangle side is integrated out. Also present an accurate and computationally efficient means of estimating the covariance matrix. With these techniques and redshift-space linear and non-linear biases are measured, with 2.6% precision on the former if sigma8 is fixed. The data also indicates a 2.8 sigma preference for the BAO, confirming the presence of BAO in the 3PCF.
1512.02636
The link between the assembly of the inner dark matter halo and the angular momentum evolution of galaxies in the EAGLE simulation
Zavala, Frenk, Bower, Schaye, et al
Explore the co-evolution of the specific angular momentum of DM haloes and the cold baryons that comprise the galaxies within. Study over 2k central galaxies within the reference cosmo hydro sim of the EAGLE project. Employ a methodology within which the evolutionary history of a system is specified by the time-evolving properties of the Lagrangian particles that define it at z=0. Find a strong correlation between the evolution of the specific angular momentum of today's stars (cold gas) and that of the inner (whole) DM halo they are associated with. This link is particularly strong for the stars formed before the epoch of maximum expansion and subsequent collapse of the central DM halo (turnaround). Spheroids are typically assembled primarily from stars formed prior to turnaround, and are therefore destined to suffer a net loss of angular momentum associated with the strong merging activity during the assembly of the inner DM halo. Stellar discs retain their specific angular momentum it acquired by tidal torques during the linear growth of the halo. Since the specific angular momentum loss of the stars is tied to the galaxy's morphology today, it may be possible to use these results to predict, statistically, the assembly history of a all given the morphology of the galaxy it hosts.
1512.02882
Planck intermediate results. XLI. A map of lensing-induced B-modes
Planck Collaboration
The lensing-induced B-mode signal is a valuable probe of the DM distribution integrated back to the last-scattering surface, with a broad kernel that peaks at z~2. It also constitutes an important contaminant for the extraction of the primary CMB B-modes from inflation. Combining all-sky coverage and high resolution and sensitivity, Planck provides accurate nearly all-sky measurements of both the polarization E-mode signal and the integrated mass distribution via the reconstruction of the CMB gravitational lensing. By combining these two data products, produce an all-sky template mass of the secondary CMB B-modes using a real-space algorithm that minimizes the impact of sky masks. The cross-correlation of this template with an observed (primordial and secondary) B-mode map can be used to measure the lensing B-mode power spectrum at all angular scales. In particular when cross-correlating with the B-mode contribution directly derived from the Planck polarization maps, obtain lensing-induced B-mode PS measurements at a significance of 12 sigma, which are in agreement with the theoretical expectation derived from the Planck best-fit LCDM model. This unique nearly all-sky secondary B-mode template, which includes the lensing-induced information from intermediate to small (10<ell<1000) angular scales, is delivered as part of the Planck 2015 public data release. It will be particularly useful for experiments searching for primordial B-modes, such as BICEP2/Keck Array or LiteBIRD, since it will enable an estimate to be made of the secondary (i.e., lensing) contribution to the measured total CMB B-modes.
1512.02231
The large-scale 3-point correlation function of the SDSS BOSS DR12 CMASS galaxies
Slepian, Eisenstein, et al
Report a measurement of the large-scale 3PCF of galaxies using the largest dataset for this purpose to date; 777k LRGs in SDSS BOSS DR12 CMASS sample. This work exploits the novel algorithm of Slepian&Eisenstein (2015) to compute the multiple moments of the 3PCF in O(N^2) time, with N the number of galaxies. Leading-order perturbation theory models the data well in a compressed basis where one triangle side is integrated out. Also present an accurate and computationally efficient means of estimating the covariance matrix. With these techniques and redshift-space linear and non-linear biases are measured, with 2.6% precision on the former if sigma8 is fixed. The data also indicates a 2.8 sigma preference for the BAO, confirming the presence of BAO in the 3PCF.
1512.02636
The link between the assembly of the inner dark matter halo and the angular momentum evolution of galaxies in the EAGLE simulation
Zavala, Frenk, Bower, Schaye, et al
Explore the co-evolution of the specific angular momentum of DM haloes and the cold baryons that comprise the galaxies within. Study over 2k central galaxies within the reference cosmo hydro sim of the EAGLE project. Employ a methodology within which the evolutionary history of a system is specified by the time-evolving properties of the Lagrangian particles that define it at z=0. Find a strong correlation between the evolution of the specific angular momentum of today's stars (cold gas) and that of the inner (whole) DM halo they are associated with. This link is particularly strong for the stars formed before the epoch of maximum expansion and subsequent collapse of the central DM halo (turnaround). Spheroids are typically assembled primarily from stars formed prior to turnaround, and are therefore destined to suffer a net loss of angular momentum associated with the strong merging activity during the assembly of the inner DM halo. Stellar discs retain their specific angular momentum it acquired by tidal torques during the linear growth of the halo. Since the specific angular momentum loss of the stars is tied to the galaxy's morphology today, it may be possible to use these results to predict, statistically, the assembly history of a all given the morphology of the galaxy it hosts.
1512.02882
Planck intermediate results. XLI. A map of lensing-induced B-modes
Planck Collaboration
The lensing-induced B-mode signal is a valuable probe of the DM distribution integrated back to the last-scattering surface, with a broad kernel that peaks at z~2. It also constitutes an important contaminant for the extraction of the primary CMB B-modes from inflation. Combining all-sky coverage and high resolution and sensitivity, Planck provides accurate nearly all-sky measurements of both the polarization E-mode signal and the integrated mass distribution via the reconstruction of the CMB gravitational lensing. By combining these two data products, produce an all-sky template mass of the secondary CMB B-modes using a real-space algorithm that minimizes the impact of sky masks. The cross-correlation of this template with an observed (primordial and secondary) B-mode map can be used to measure the lensing B-mode power spectrum at all angular scales. In particular when cross-correlating with the B-mode contribution directly derived from the Planck polarization maps, obtain lensing-induced B-mode PS measurements at a significance of 12 sigma, which are in agreement with the theoretical expectation derived from the Planck best-fit LCDM model. This unique nearly all-sky secondary B-mode template, which includes the lensing-induced information from intermediate to small (10<ell<1000) angular scales, is delivered as part of the Planck 2015 public data release. It will be particularly useful for experiments searching for primordial B-modes, such as BICEP2/Keck Array or LiteBIRD, since it will enable an estimate to be made of the secondary (i.e., lensing) contribution to the measured total CMB B-modes.
Tuesday, December 8, 2015
Day 1020
Wednesday.
1512.01253
How does the choice of observable influence our estimation of the centre of a galaxy cluster? Insights from cosmological simulations
Cui, Power, Biffi, Borgani, Knabe, Murante, Fabjan, Lewis, Poole
Galaxy clusters are an established and powerful test-bed for theories of both galaxy evolution and cosmology. Accurate interpretation of cluster observations often requires robust identification of the location of the centre. Using a statistical sample of clusters drawn from a suit of cosmo sims in which a range of galaxy formation models are explored, investigate how the location of this centre is affected by the choice of observable - stars, hot gas, or the full mass distribution as can be probed by the gravitational potential. Explore several measures of cluster centre: the minimum of the gravitational potential, which would expect to define the centre if the cluster is in dynamical equilibrium; the peak of the density; the centre of BCG; and the peak and centroid of X-ray luminosity. Find that the centre of BCG correlates more strongly with the minimum of the gravitational potential than the X-ray defined centre, while AGN feedback acts to significantly enhance the offset between the peak X-ray luminosity and minimum gravitational potential. These results highlight the importance of centre identification when interpreting clusters observations, in particular when comparing theoretical predications and observational data.
1512.02219
Vertical disc heating in Milky Way-sized galaxies in a cosmological context
Grand, Springel, Gómez, Marinucci, Pakmor, Campbell, Jenkins
Vertically extended, high velocity dispersion stellar distributions appear to be a ubiquitous feature of disc galaxies, and both internal and external mechanisms have been proposed to be the major driver of their formation. However, it is unclear to what extent each mechanism can generate such a distribution, which is likely to depend on the assembly history of the galaxy. To this end, perform 16 high res cosmos-zoom simulations of MW-sized galaxies using the state-of-the-art cosmological magneto-hydrodynamical code REPO, and analyse the evolution of the vertical kinematics of the stellar disc in connection with various heating mechanisms. Find that the bar is the dominant heating mechanism in most cases, whereas spiral arms, radial migration, and adiabatic heating from mid-plane density growth are all sub-dominant. The strongest source, though less prevalent than bars, originates from external perturbations from satellite/sub-haloes of masses log10(M/Msun)>10. However, in many simulations the orbits of newborn star particles become cooler with time, such that they dominate the shape of the age-velocity dispersion relation and overall vertical disc structure unless a strong external perturbation takes place.
1512.02236
The alignment of galaxy spin with the shear field in observations
Pahoa, Libeskind, Tempel, Hoffman, Tully, et al
Tidal torque theory suggests that galaxies gain angular momentum in the linear stage of structure formation. Such a theory predicts alignments between the spin of haloes and tidal shear field. However, NL evolution and angular momentum acquisition may later this prediction significantly. In this paper, use a reconstruction of the cosmic shear field from observed peculiar velocities combined with spin axes extracted from galaxies within 115 Mpc (~8000 km/s) from 2MRS catalog, to test whether or not galaxies appear aligned with principal axes of shear field. Although linear reconstructions of the tidal field have looked at similar issues, this is the first such study to examine galaxy alignments with velocity-shear field. Ellipticals in the 2MRS sample, show a statistically significant alignment with tow of the principal axes of the shear field. In general, elliptical galaxies have their short axis aligned with the axis of greatest compression and perpendicular to the axis of slowest compression. Spiral galaxies show no signal. Such an alignment is significantly strengthened when considering only those galaxies that are used in velocity field reconstruction. When examining such a subsample, a weak alignment with the axis of greatest compression emerges for spiral galaxies as well. This result indicates that although velocity field reconstructions still rely on family noisy and sparse data, the underlying alignment with shear field is strong enough to be visible even when small numbers of galaxies are considered - especially if those galaxies are used as constraints in the reconstruction.
1512.02342
Galaxy and Mass Assembly (GAMA): the stellar mass budget by galaxy type
Moffatt, et al
Report an expanded sample of visual morphological classifications from GAMA phase two, which now includes 7556 objects (previously 3727 in phase one). Define a local (z<0.06) sample and classify galaxies into E, S0-Sa, SB0-SBa, Sab-Scd, SBabSBcd, Sd-Irr, and "little blue spheroid" types. Using these updated classifications, derive stellar mass function fits to individual galaxy populations divided both by morphological class and more general spheroid- or disk-dominated categories with a lower mass limit of log(M*/Msun)=8 (on dex below earlier morphological mass function determinations). Find that all individual morphological classes and the combined spheroid-/bulge-dominated classes are well described by single Schechter stellar mass function forms. Find that the total stellar mass densities for individual galaxy populations and for the entire galaxy population are bounded within the stellar mass limits and derive an estimated total stellar mass density of rho_star = 2.5e8 Msun h_0.7/Mpc^3, which corresponds to an approximately 4% fraction of baryons found in stars. The mass contributions to this total stellar mass density by galaxies that are dominated by spheroidal components (E and S0-Sa classes) and by disk components (Sab-Scd and Sd-Irr classes) are approximately 70% and 30%, respectively.
1512.01253
How does the choice of observable influence our estimation of the centre of a galaxy cluster? Insights from cosmological simulations
Cui, Power, Biffi, Borgani, Knabe, Murante, Fabjan, Lewis, Poole
Galaxy clusters are an established and powerful test-bed for theories of both galaxy evolution and cosmology. Accurate interpretation of cluster observations often requires robust identification of the location of the centre. Using a statistical sample of clusters drawn from a suit of cosmo sims in which a range of galaxy formation models are explored, investigate how the location of this centre is affected by the choice of observable - stars, hot gas, or the full mass distribution as can be probed by the gravitational potential. Explore several measures of cluster centre: the minimum of the gravitational potential, which would expect to define the centre if the cluster is in dynamical equilibrium; the peak of the density; the centre of BCG; and the peak and centroid of X-ray luminosity. Find that the centre of BCG correlates more strongly with the minimum of the gravitational potential than the X-ray defined centre, while AGN feedback acts to significantly enhance the offset between the peak X-ray luminosity and minimum gravitational potential. These results highlight the importance of centre identification when interpreting clusters observations, in particular when comparing theoretical predications and observational data.
1512.02219
Vertical disc heating in Milky Way-sized galaxies in a cosmological context
Grand, Springel, Gómez, Marinucci, Pakmor, Campbell, Jenkins
Vertically extended, high velocity dispersion stellar distributions appear to be a ubiquitous feature of disc galaxies, and both internal and external mechanisms have been proposed to be the major driver of their formation. However, it is unclear to what extent each mechanism can generate such a distribution, which is likely to depend on the assembly history of the galaxy. To this end, perform 16 high res cosmos-zoom simulations of MW-sized galaxies using the state-of-the-art cosmological magneto-hydrodynamical code REPO, and analyse the evolution of the vertical kinematics of the stellar disc in connection with various heating mechanisms. Find that the bar is the dominant heating mechanism in most cases, whereas spiral arms, radial migration, and adiabatic heating from mid-plane density growth are all sub-dominant. The strongest source, though less prevalent than bars, originates from external perturbations from satellite/sub-haloes of masses log10(M/Msun)>10. However, in many simulations the orbits of newborn star particles become cooler with time, such that they dominate the shape of the age-velocity dispersion relation and overall vertical disc structure unless a strong external perturbation takes place.
1512.02236
The alignment of galaxy spin with the shear field in observations
Pahoa, Libeskind, Tempel, Hoffman, Tully, et al
Tidal torque theory suggests that galaxies gain angular momentum in the linear stage of structure formation. Such a theory predicts alignments between the spin of haloes and tidal shear field. However, NL evolution and angular momentum acquisition may later this prediction significantly. In this paper, use a reconstruction of the cosmic shear field from observed peculiar velocities combined with spin axes extracted from galaxies within 115 Mpc (~8000 km/s) from 2MRS catalog, to test whether or not galaxies appear aligned with principal axes of shear field. Although linear reconstructions of the tidal field have looked at similar issues, this is the first such study to examine galaxy alignments with velocity-shear field. Ellipticals in the 2MRS sample, show a statistically significant alignment with tow of the principal axes of the shear field. In general, elliptical galaxies have their short axis aligned with the axis of greatest compression and perpendicular to the axis of slowest compression. Spiral galaxies show no signal. Such an alignment is significantly strengthened when considering only those galaxies that are used in velocity field reconstruction. When examining such a subsample, a weak alignment with the axis of greatest compression emerges for spiral galaxies as well. This result indicates that although velocity field reconstructions still rely on family noisy and sparse data, the underlying alignment with shear field is strong enough to be visible even when small numbers of galaxies are considered - especially if those galaxies are used as constraints in the reconstruction.
1512.02342
Galaxy and Mass Assembly (GAMA): the stellar mass budget by galaxy type
Moffatt, et al
Report an expanded sample of visual morphological classifications from GAMA phase two, which now includes 7556 objects (previously 3727 in phase one). Define a local (z<0.06) sample and classify galaxies into E, S0-Sa, SB0-SBa, Sab-Scd, SBabSBcd, Sd-Irr, and "little blue spheroid" types. Using these updated classifications, derive stellar mass function fits to individual galaxy populations divided both by morphological class and more general spheroid- or disk-dominated categories with a lower mass limit of log(M*/Msun)=8 (on dex below earlier morphological mass function determinations). Find that all individual morphological classes and the combined spheroid-/bulge-dominated classes are well described by single Schechter stellar mass function forms. Find that the total stellar mass densities for individual galaxy populations and for the entire galaxy population are bounded within the stellar mass limits and derive an estimated total stellar mass density of rho_star = 2.5e8 Msun h_0.7/Mpc^3, which corresponds to an approximately 4% fraction of baryons found in stars. The mass contributions to this total stellar mass density by galaxies that are dominated by spheroidal components (E and S0-Sa classes) and by disk components (Sab-Scd and Sd-Irr classes) are approximately 70% and 30%, respectively.
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