Tuesday.
1501.05950
The contributions of matter inside and outside of haloes to the matter power spectrum
van Daalen, Schaye
Halo-based models have been successful in predicting the clustering of matter, but the validity of the postulate that the clustering is fully determined by matter inside haloes remains largely untested, and it is not clear a priori whether non-virialised matter might contribute significantly to the NL clustering signal. Investigate the contribution of haloes to the matter PS as a function of both sale and halo mass by combining a set of cosmo N-body sims to calculate the contributions of different spherical overdensity regions, FoF groups and matter outside haloes to the PS. Find that matter inside spherical overdensity regions of size R200m cannot account for all power for 1<k<100 h/Mpc, regardless of the minimum halo mass. At most, it accounts for 95% of the power (k>20 h/Mpc). For 2<k<10 h/Mpc, haloes with mass M200m<1e11 Msunh contribute negligibly to the PS, and the results appear to be converged with decreasing halo mass. When haloes are taken to be regions of size R020c, the amount of power unaccounted for is larger on all scales. Accounting also for matter inside for groups but outside R200m increases the contribution of halo matter on most scales probed here by 5-15%. Matter inside FoF groups with M200m>1e9 Msun/h accounts for essentially all power for 3<k<100 h/Mpc. Therefore expect halo models that ignore the contribution of matter outside R200m to overestimate the contribution of haloes of any mass to the power on small scales (k>1 h/Mpc).
Monday, January 26, 2015
Sunday, January 25, 2015
Day 823
Monday.
1501.05736
Optical technologies for the observation of low Earth orbit objects
Hampf, Wagner, Riede
To avoid collisions with space debris, the near Earth orbit must be continuously scanned by other ground- or spaced-based facilities. For the low Earth orbit, radar telescopes are the workhorse for this task, especially due to their continuous availability. However, optical observation methods can deliver complementary information, especially towards high accuracy measurements. Passive-optical observations are inexpensive and can yield very precise information about the apparent position of the object in the sky via comparison with background stars. However, the object's distance from the observer is not readily accessible, which constitutes a major drawback of this approach for the precise calculation of the orbital elements. Two experimental methods have been devised to overcome this problem: using two observatories a few kilometers apart, strictly simultaneous observations of the same object yield an accurate, instantaneous 3d position determination through measurement of the parallax. If only one observatory is available, a pulsed laser can be used in addition to the passive-optical channel to measure the distance to the object, in a similar fashion as used by the satellite laser ranging community. However, compared to conventional laser ranging, a stronger laser and more elaborate tracking algorithms are necessary. The two approaches can also be combined by illuminating the object with a pulsed laser from one observatory and measuring the return times at both observatories. These techniques are explored by German Aerospace Center in Stuttgart using its orbital debris research observatory, in cooperation with the Satellite Laser Ranging station in Graz and the Geodetic Observatory in Wettzell. This contribution will present some of the results and plans for further measurement campaigns.
1501.05736
Optical technologies for the observation of low Earth orbit objects
Hampf, Wagner, Riede
To avoid collisions with space debris, the near Earth orbit must be continuously scanned by other ground- or spaced-based facilities. For the low Earth orbit, radar telescopes are the workhorse for this task, especially due to their continuous availability. However, optical observation methods can deliver complementary information, especially towards high accuracy measurements. Passive-optical observations are inexpensive and can yield very precise information about the apparent position of the object in the sky via comparison with background stars. However, the object's distance from the observer is not readily accessible, which constitutes a major drawback of this approach for the precise calculation of the orbital elements. Two experimental methods have been devised to overcome this problem: using two observatories a few kilometers apart, strictly simultaneous observations of the same object yield an accurate, instantaneous 3d position determination through measurement of the parallax. If only one observatory is available, a pulsed laser can be used in addition to the passive-optical channel to measure the distance to the object, in a similar fashion as used by the satellite laser ranging community. However, compared to conventional laser ranging, a stronger laser and more elaborate tracking algorithms are necessary. The two approaches can also be combined by illuminating the object with a pulsed laser from one observatory and measuring the return times at both observatories. These techniques are explored by German Aerospace Center in Stuttgart using its orbital debris research observatory, in cooperation with the Satellite Laser Ranging station in Graz and the Geodetic Observatory in Wettzell. This contribution will present some of the results and plans for further measurement campaigns.
Thursday, January 22, 2015
Day 822
Friday.
1501.05520
Halo mass distribution reconstruction across the cosmic web
Zhao, et al
Study the relation between halo mass and its environment from a probabilistic perspective. Find that halo mass depends not only on local DM density, but also on non-local quantities such as the cosmic web environment and the halo-exclusion effect. Given these accurate relations, develop the HADRON-code (Halo mAss Distribution ReconstructiON), a technique which permits assigning halo masses to a distribution of haloes in 3d. This can be applied to the fast production of mock galaxy catalogues, by assigning halo masses, and reproducing accurately the bias for different mass cuts. The resulting clustering of the halo populations agree well with that drawn from the BigMultiDark N-body simulation: the power spectra are within 1-sigma up to scales of k=0.2 h/Mpc, when using augmented Lagrangian perturbation theory based mock catalogues. Only the most massive haloes show a larger deviation. For these, find evidence of the halo-exclusion effect. A clear improvement is achieved when assigning the highest masses to haloes with a minimum distance separation. Also compute the 2- and 3-pt correlation functions, and find an excellent agreement with N-body results. The work represents a quantitative application of the cosmic web classification. It can have further interesting applications in the multi-tracer analysis of the large-scale structure for future galaxy surveys.
1501.05571
The information content of anisotropic baryon acoustic oscillation scale measurements
Ross, Percival, Manera
Show: measurements mead using either the monopole and quadrupole, or the monopole and mu^2 power-law moment, are optimal for anisotropic BAO measurements, in that they contain all of the available information using two moments, the minimal number required to measure both H(z) and D_A(z). Test predictions using 600 mock galaxy samples, finding a good match to the analytic predictions. Results should enable the optimal extraction of information from future galaxy surveys such as eBOSS, DESI and Euclid.
1501.05520
Halo mass distribution reconstruction across the cosmic web
Zhao, et al
Study the relation between halo mass and its environment from a probabilistic perspective. Find that halo mass depends not only on local DM density, but also on non-local quantities such as the cosmic web environment and the halo-exclusion effect. Given these accurate relations, develop the HADRON-code (Halo mAss Distribution ReconstructiON), a technique which permits assigning halo masses to a distribution of haloes in 3d. This can be applied to the fast production of mock galaxy catalogues, by assigning halo masses, and reproducing accurately the bias for different mass cuts. The resulting clustering of the halo populations agree well with that drawn from the BigMultiDark N-body simulation: the power spectra are within 1-sigma up to scales of k=0.2 h/Mpc, when using augmented Lagrangian perturbation theory based mock catalogues. Only the most massive haloes show a larger deviation. For these, find evidence of the halo-exclusion effect. A clear improvement is achieved when assigning the highest masses to haloes with a minimum distance separation. Also compute the 2- and 3-pt correlation functions, and find an excellent agreement with N-body results. The work represents a quantitative application of the cosmic web classification. It can have further interesting applications in the multi-tracer analysis of the large-scale structure for future galaxy surveys.
1501.05571
The information content of anisotropic baryon acoustic oscillation scale measurements
Ross, Percival, Manera
Show: measurements mead using either the monopole and quadrupole, or the monopole and mu^2 power-law moment, are optimal for anisotropic BAO measurements, in that they contain all of the available information using two moments, the minimal number required to measure both H(z) and D_A(z). Test predictions using 600 mock galaxy samples, finding a good match to the analytic predictions. Results should enable the optimal extraction of information from future galaxy surveys such as eBOSS, DESI and Euclid.
Wednesday, January 21, 2015
Day 821
Thursday.
1501.04977
Quiescent compact galaxies at intermediate redshift in the COSMOS field II. The fundamental plane of massive galaxies
Zahid, et al
~150 massive quiescent galaxies with an average sigma ~ 250 km/s and 0.2<z>0.8. More than half of the galaxies in the sample are compact. The COSMOS galaxies exhibit a tight relation (~0.1 dex scatter) between surface brightness, velocity dispersion and size. At a fixed combination of velocity dispersion and size, the COSMOS galaxies are brighter than galaxies in the local universe. The surface brightness offsets are correlated with the rest-frame g-z color and D_n4000 index; bluer galaxies and those with smaller D_n4000 indices have larger offsets. Stellar population synthesis models indicate that the massive COSMOS galaxies are younger and therefore brighter than similarly massive quiescent galaxies in the local universe. Passive evolution alone brings the massive compact quiescent COSMOS galaxies into the local fundamental plane at z=0. Therefore, evolution in size or velocity dispersion for massive compact quiescent galaxies since z~1 is constrained by the small scatter observed in the fundamental plane. Conclude that massive compact quiescent galaxies at z<~1 are not a special class of objects but rather the tail of the mass and size distribution of the normal quiescent galaxy population.
1501.04977
Quiescent compact galaxies at intermediate redshift in the COSMOS field II. The fundamental plane of massive galaxies
Zahid, et al
~150 massive quiescent galaxies with an average sigma ~ 250 km/s and 0.2<z>0.8. More than half of the galaxies in the sample are compact. The COSMOS galaxies exhibit a tight relation (~0.1 dex scatter) between surface brightness, velocity dispersion and size. At a fixed combination of velocity dispersion and size, the COSMOS galaxies are brighter than galaxies in the local universe. The surface brightness offsets are correlated with the rest-frame g-z color and D_n4000 index; bluer galaxies and those with smaller D_n4000 indices have larger offsets. Stellar population synthesis models indicate that the massive COSMOS galaxies are younger and therefore brighter than similarly massive quiescent galaxies in the local universe. Passive evolution alone brings the massive compact quiescent COSMOS galaxies into the local fundamental plane at z=0. Therefore, evolution in size or velocity dispersion for massive compact quiescent galaxies since z~1 is constrained by the small scatter observed in the fundamental plane. Conclude that massive compact quiescent galaxies at z<~1 are not a special class of objects but rather the tail of the mass and size distribution of the normal quiescent galaxy population.
Tuesday, January 20, 2015
Day 820
Wednesday.
1501.04650
Cool core bias in Sunyaev-Zel'dovich galaxy cluster surveys
Lin, McDonald, Benson, MIller
Estimate the effect on the observed SZ signal of centrally-peaked gas density profiles (cool cores) and radio emission from the BCG by creating mock observations of sample of clusters that span the observed range of classical cooling rates and radio luminosities. Find that the inclusion of a cool core can cause a change in the measured SPT significant of a cluster between 0.01% - 10% at z>0.3, increasing with cuspiness of the cool core and angular size on the sky of the cluster (i.e., decreasing redshift, increasing mass). Provide quantitative estimates of the bias in the SZ signal as a function of a gas density cushiness parameter, z, mass and the 1.4 GHz radio luminosity of the central AGN. Based on this work, estimate that for the Phoenix cluster (one of the strongest cool cores known), the presence of a cool core is biasing the SZ significance high by ~6%. The ubiquity of radio galaxies at the centers of cool core clusters will offset the cool core bias to varying degrees.
1501.04733
Improving the LSST dithering pattern and cadence for dark energy studies
Carroll, Gawiser, ... et al
LSST: observed the entire southern sky over 10 years starting in 2022 in 6 liters, grizzly, with unprecedented depth and time sampling. Artificial power on the scale of 2.5 deg LSST FoV will contaminate measurements of BAO, which fall at the same angular scale at z~1. Using the HEALPix framework, demonstrate the impact of an "un-dithered" sure, in which 17% of each LSST FoV is overlapped by neighboring observations, generating a honeycomb pattern of strongly varying survey depth and significant artificial power on BAO angular scales. Find that adopting large dithers of amplitude close to the LSST FoV radius reduces artificial structure in the galaxy distribution by a factor of ~10. Propose an observing strategy utilizing large dithers within the main survey and minimal dithers for the LSST Deep Driling Fields. Show that applying various magnitude cutoffs can further increase survey uniformity. Find that a magnitude cut of r<27.3 remove significant spurious power from the angular PS with a minimal reduction in the total number of observed galaxies over the ten-year LSST run . Also determine the effectiveness of the observing strategy for SNeIa and predict that the main survey will contribute ~100k SNeIa. Propose a concentrated survey where LSST observes 1/3 of its main survey area each year, increasing the number of main survey SNeIa by a factor of ~1.5, while still enabling the successful pursuit of other science drivers.
1501.04650
Cool core bias in Sunyaev-Zel'dovich galaxy cluster surveys
Lin, McDonald, Benson, MIller
Estimate the effect on the observed SZ signal of centrally-peaked gas density profiles (cool cores) and radio emission from the BCG by creating mock observations of sample of clusters that span the observed range of classical cooling rates and radio luminosities. Find that the inclusion of a cool core can cause a change in the measured SPT significant of a cluster between 0.01% - 10% at z>0.3, increasing with cuspiness of the cool core and angular size on the sky of the cluster (i.e., decreasing redshift, increasing mass). Provide quantitative estimates of the bias in the SZ signal as a function of a gas density cushiness parameter, z, mass and the 1.4 GHz radio luminosity of the central AGN. Based on this work, estimate that for the Phoenix cluster (one of the strongest cool cores known), the presence of a cool core is biasing the SZ significance high by ~6%. The ubiquity of radio galaxies at the centers of cool core clusters will offset the cool core bias to varying degrees.
1501.04733
Improving the LSST dithering pattern and cadence for dark energy studies
Carroll, Gawiser, ... et al
LSST: observed the entire southern sky over 10 years starting in 2022 in 6 liters, grizzly, with unprecedented depth and time sampling. Artificial power on the scale of 2.5 deg LSST FoV will contaminate measurements of BAO, which fall at the same angular scale at z~1. Using the HEALPix framework, demonstrate the impact of an "un-dithered" sure, in which 17% of each LSST FoV is overlapped by neighboring observations, generating a honeycomb pattern of strongly varying survey depth and significant artificial power on BAO angular scales. Find that adopting large dithers of amplitude close to the LSST FoV radius reduces artificial structure in the galaxy distribution by a factor of ~10. Propose an observing strategy utilizing large dithers within the main survey and minimal dithers for the LSST Deep Driling Fields. Show that applying various magnitude cutoffs can further increase survey uniformity. Find that a magnitude cut of r<27.3 remove significant spurious power from the angular PS with a minimal reduction in the total number of observed galaxies over the ten-year LSST run . Also determine the effectiveness of the observing strategy for SNeIa and predict that the main survey will contribute ~100k SNeIa. Propose a concentrated survey where LSST observes 1/3 of its main survey area each year, increasing the number of main survey SNeIa by a factor of ~1.5, while still enabling the successful pursuit of other science drivers.
Monday, January 19, 2015
Day 819
Tuesday.
1501.04104
Bluk flows and end of the dark ages with the SKA
Maio, Ciardi, Koopmans
The early Universe is a probe of the birth of primordial objects, first SF events and consequent production of photons and heavy elements. Higher-order corrections to the cosmological linear perturbation theory predicts the formation of coherent supersonic gases streaming motions at decoupling time. These bulk flows impact the gas cooling process and determine a cascade effect on the whole baryon evolution. By analytical estimates and N-body hydrodynamical chemistry numerical simulations including atomic an molecular evolution, gas cooling, SF, feedback effects and metal spreading for individual species from different stellar populations according to the proper yields and lifetimes, discuss the role of these primordial bulk flows at the end of the dark ages and their detectable impacts during the first GYr in view of the upcoming SKA mission. Early bulk flows can inhibit molecular gas cooling capabilities, suppressing SF, metal spreading and the abundance of small primordial galaxies in the infant Universe. This can determine a delay in the re-ionization process and in the heating of neutral hydrogen making the observable HI signal during cosmic evolution patchier and noisier. The planned SKA mission will represent a major advance over existing instruments, since it will be able to probe the effects on HI 21cm at z~6-20 and on molecular ling emissions from first collapsing sites at z~20-40. Therefore, it will be optimal to address the effects of primordial streaming motions on early baryon evolution and to give constraints on structure formation in the first Gyr.
1501.04105
The bias of the submillimetre galaxy population: SMGs are poor tracers of the most massive structures n the z~2 universe
Miller, ... Behroozi et al
From Bolshoi cosmo sims, find that SMGs exhibit a relatively complex bias: some regions of high SMG overdensity are underdense in terms of DM mass, and some regions of high DM overdensity contain no SMGs. Because of their rarity, Poisson noise causes scattering the SMG overdensity at fixed DM overdensity. Consequently, rich associations of less-luminous, more-abundant galaxies (i.e., Lyman-break galaxy analogues) trace the highest DM over densities because of 'downsizing': at z<~2.5, the most-massive galaxies that reside in the highest DM over densities have already had their SF quenched and are thus no longer SMGs. Furthermore, because of Poisson noise and downsizing, some of the highest over densities are not associated with any SMGs. Conversely, some bright SMGs are in underdense regions.
1501.04104
Bluk flows and end of the dark ages with the SKA
Maio, Ciardi, Koopmans
The early Universe is a probe of the birth of primordial objects, first SF events and consequent production of photons and heavy elements. Higher-order corrections to the cosmological linear perturbation theory predicts the formation of coherent supersonic gases streaming motions at decoupling time. These bulk flows impact the gas cooling process and determine a cascade effect on the whole baryon evolution. By analytical estimates and N-body hydrodynamical chemistry numerical simulations including atomic an molecular evolution, gas cooling, SF, feedback effects and metal spreading for individual species from different stellar populations according to the proper yields and lifetimes, discuss the role of these primordial bulk flows at the end of the dark ages and their detectable impacts during the first GYr in view of the upcoming SKA mission. Early bulk flows can inhibit molecular gas cooling capabilities, suppressing SF, metal spreading and the abundance of small primordial galaxies in the infant Universe. This can determine a delay in the re-ionization process and in the heating of neutral hydrogen making the observable HI signal during cosmic evolution patchier and noisier. The planned SKA mission will represent a major advance over existing instruments, since it will be able to probe the effects on HI 21cm at z~6-20 and on molecular ling emissions from first collapsing sites at z~20-40. Therefore, it will be optimal to address the effects of primordial streaming motions on early baryon evolution and to give constraints on structure formation in the first Gyr.
1501.04105
The bias of the submillimetre galaxy population: SMGs are poor tracers of the most massive structures n the z~2 universe
Miller, ... Behroozi et al
From Bolshoi cosmo sims, find that SMGs exhibit a relatively complex bias: some regions of high SMG overdensity are underdense in terms of DM mass, and some regions of high DM overdensity contain no SMGs. Because of their rarity, Poisson noise causes scattering the SMG overdensity at fixed DM overdensity. Consequently, rich associations of less-luminous, more-abundant galaxies (i.e., Lyman-break galaxy analogues) trace the highest DM over densities because of 'downsizing': at z<~2.5, the most-massive galaxies that reside in the highest DM over densities have already had their SF quenched and are thus no longer SMGs. Furthermore, because of Poisson noise and downsizing, some of the highest over densities are not associated with any SMGs. Conversely, some bright SMGs are in underdense regions.
Sunday, January 18, 2015
Day 818
Monday.
1501.03822
Real time cosmology - a direct measure of the expansion rate of the Universe
Klöckner et al
The SKA enables an ultimate test in cosmology by measuring the expansion rate of the Universe in real time. This can be done by a rather simple experiment of observing the neutral hydrogen (HI) signal of galaxies at two different epochs. The signal will encounter a change in frequency imprinted as the Universe expands over time and thus monitoring the drift in frequencies will provide a real time measure of the cosmic acceleration. Over a period of 12 years, one would expect a frequency shift of the order 0.1 Hz assuming a standard LCDM cosmology. Based on the sensitivity estimates of the SKA and the number counts of the expected HI galaxies, it is shown that the number counts are sufficiently high to compensate for the observational uncertainties of the measurements and hence allow a statistical detection of the frequency shift.
1501.03828
Weak gravitational lensing with the Square Kilometre Array
Brown, Bacon, .. Harrison, Joachim, Metcalfe, ... Zuntz, Abdalla, Bridle, Jarvis, Kitching, Miller, et al
Investigate the capabilities of various stages of the SKA to perform world-leading weak gravitational lensing surveys. Outline a way forward to develop the tools needed for pursuing weak lensing in the radio band. Identify the key analysis challenges and the key pathfinder experiments that will allow to address them in the run up to the SKA. Identify and summarize the unique and potentially very powerful aspects of radio weak lensing surveys, facilitated by the SKA, that can solve major challenges in the field of WL. These include the use of polarization and rotational velocity information to control IA, and the new area of WL using intensity mapping experiments. Show how the SKA lensing surveys will both complement and enhance corresponding efforts in the optical wavebands through cross-correlation techniques and by way of extending the reach of WL to high z.
1501.03848
Cross correlation surveys with the Square Kilometre Array
Kirk, Benoit-Lévy, Abdalla, Bull, Joachimi
SKA will be able to perform state of the art LSS as well as WL measurements of the distribution of matter in the Universe. Concentrate on the synergies that result from cross-correlating these different SKA data products as well as external correlation with the WL measurements available from CMB missions. Show that the DE FoM obtained individually from WL/LSS measurements and their independent combination is significantly increased when their full cross-correlations are taken in to account. This is due to the increased knowledge of galaxy bias as a function of z as well as the extra information from the different cosmological dependences of the cross-correlations. Show that the cross-correlation between a spectroscopic LSS sample and a WL sample with photometric z can calibrate these same photometric z, and their scatter, to high accuracy by modeling them as nuisance parameters and fitting them simultaneously. Finally, show that Modified Gravity parameters are greatly constrained by this cross-correlations because WL and z-space distortions (from LSS survey) break strong degeneracies in common parameterizations of modified gravity.
1501.03977
Synergy between the Large Synoptic Survey Telescope and the Square Kilometer Array
Bacon, Bridle, Abdalla, ... et al
Describe how WL and galaxy clustering studies with LSST and SKA can provide improved constraints on the causes of the cosmological acceleration. Summarize the benefits to galaxy evolution studies of combining deep optical multi-band imaging with radio observations. Discuss the excellent match between one of the most unique features of the LSST, its temporal cadence in the optical waveband, and the time resolution of the SKA.
1501.03978
Euclid & SKA Symergies
Kitching, et al
The two experiments are synergistic in several respects, both through the scientific objectives and through the control of systematic effects. SKA Phase-1 and Euclid will be commissioned on similar timescales offering an exciting opportunity to exploit synergies between these facilities.
1501.03822
Real time cosmology - a direct measure of the expansion rate of the Universe
Klöckner et al
The SKA enables an ultimate test in cosmology by measuring the expansion rate of the Universe in real time. This can be done by a rather simple experiment of observing the neutral hydrogen (HI) signal of galaxies at two different epochs. The signal will encounter a change in frequency imprinted as the Universe expands over time and thus monitoring the drift in frequencies will provide a real time measure of the cosmic acceleration. Over a period of 12 years, one would expect a frequency shift of the order 0.1 Hz assuming a standard LCDM cosmology. Based on the sensitivity estimates of the SKA and the number counts of the expected HI galaxies, it is shown that the number counts are sufficiently high to compensate for the observational uncertainties of the measurements and hence allow a statistical detection of the frequency shift.
1501.03828
Weak gravitational lensing with the Square Kilometre Array
Brown, Bacon, .. Harrison, Joachim, Metcalfe, ... Zuntz, Abdalla, Bridle, Jarvis, Kitching, Miller, et al
Investigate the capabilities of various stages of the SKA to perform world-leading weak gravitational lensing surveys. Outline a way forward to develop the tools needed for pursuing weak lensing in the radio band. Identify the key analysis challenges and the key pathfinder experiments that will allow to address them in the run up to the SKA. Identify and summarize the unique and potentially very powerful aspects of radio weak lensing surveys, facilitated by the SKA, that can solve major challenges in the field of WL. These include the use of polarization and rotational velocity information to control IA, and the new area of WL using intensity mapping experiments. Show how the SKA lensing surveys will both complement and enhance corresponding efforts in the optical wavebands through cross-correlation techniques and by way of extending the reach of WL to high z.
1501.03848
Cross correlation surveys with the Square Kilometre Array
Kirk, Benoit-Lévy, Abdalla, Bull, Joachimi
SKA will be able to perform state of the art LSS as well as WL measurements of the distribution of matter in the Universe. Concentrate on the synergies that result from cross-correlating these different SKA data products as well as external correlation with the WL measurements available from CMB missions. Show that the DE FoM obtained individually from WL/LSS measurements and their independent combination is significantly increased when their full cross-correlations are taken in to account. This is due to the increased knowledge of galaxy bias as a function of z as well as the extra information from the different cosmological dependences of the cross-correlations. Show that the cross-correlation between a spectroscopic LSS sample and a WL sample with photometric z can calibrate these same photometric z, and their scatter, to high accuracy by modeling them as nuisance parameters and fitting them simultaneously. Finally, show that Modified Gravity parameters are greatly constrained by this cross-correlations because WL and z-space distortions (from LSS survey) break strong degeneracies in common parameterizations of modified gravity.
1501.03977
Synergy between the Large Synoptic Survey Telescope and the Square Kilometer Array
Bacon, Bridle, Abdalla, ... et al
Describe how WL and galaxy clustering studies with LSST and SKA can provide improved constraints on the causes of the cosmological acceleration. Summarize the benefits to galaxy evolution studies of combining deep optical multi-band imaging with radio observations. Discuss the excellent match between one of the most unique features of the LSST, its temporal cadence in the optical waveband, and the time resolution of the SKA.
1501.03978
Euclid & SKA Symergies
Kitching, et al
The two experiments are synergistic in several respects, both through the scientific objectives and through the control of systematic effects. SKA Phase-1 and Euclid will be commissioned on similar timescales offering an exciting opportunity to exploit synergies between these facilities.
Thursday, January 15, 2015
Day 817
Friday.
1501.03509
Exploring degeneracies in modified gravity with weak lensing
Leonard, Baker, Ferreira
By considering linear-order departures from GR, compute a novel expression for the WL convergence PS under alternative theories of gravity. This comprises and integral over a 'kernel' of GR quantities multiplied by a theory-dependent 'source' term. The clear separation between theory-independent and -dependent terms allows for an explicit understanding of each physical effect introduced by altering the theory of gravity. Take advantage of this to explore the degeneracies between gravitation parameters in WL observations.
1501.03573
Mapping galaxy encounters in numerical simulations: the spatial extent of induced star formation
Moreno, ... Hernquist
Employ a suite of 75 simulations of galaxies in idealized major mergers (M* ratio ~2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced SF. Although the total SF in galaxy encounters is generally elevated relative to isolated galaxies, find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at large galacto-cenetric radii. The radial dependence of the SF enhancement is stronger in the less massive galaxy than in the primary, and is also more pronounced in mergers of more closely aligned disc spin orientations. Conversely, these trends are almost entirely independent of the encounter's impact parameter and orbital eccentricity. Predictions of the radial dependence of triggered SF, and specifically the suppression of SF beyond kpc-scales, will be testable with the next generation of IFS surveys.
1501.03509
Exploring degeneracies in modified gravity with weak lensing
Leonard, Baker, Ferreira
By considering linear-order departures from GR, compute a novel expression for the WL convergence PS under alternative theories of gravity. This comprises and integral over a 'kernel' of GR quantities multiplied by a theory-dependent 'source' term. The clear separation between theory-independent and -dependent terms allows for an explicit understanding of each physical effect introduced by altering the theory of gravity. Take advantage of this to explore the degeneracies between gravitation parameters in WL observations.
1501.03573
Mapping galaxy encounters in numerical simulations: the spatial extent of induced star formation
Moreno, ... Hernquist
Employ a suite of 75 simulations of galaxies in idealized major mergers (M* ratio ~2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced SF. Although the total SF in galaxy encounters is generally elevated relative to isolated galaxies, find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at large galacto-cenetric radii. The radial dependence of the SF enhancement is stronger in the less massive galaxy than in the primary, and is also more pronounced in mergers of more closely aligned disc spin orientations. Conversely, these trends are almost entirely independent of the encounter's impact parameter and orbital eccentricity. Predictions of the radial dependence of triggered SF, and specifically the suppression of SF beyond kpc-scales, will be testable with the next generation of IFS surveys.
Day 816
Thursday.
1501.03155
Gusty, gaseous flows of FIRE: galactic winds in cosmological simulations with explicit stellar feedback
Muratov, ... Hopkins, Quataert, Murray
Present an analysis of the galaxy-scale gaseous outflows from the Feedback in Realistic Environments (FIRE) sims. This suite of hydrodynamic cosmological zoom simulations provides a sample of haloes where SF giant molecular clouds are resolved to z=0, and features an explicit stellar feedback model on small scales. In this work, focus on quantifying the gas mass ejected out of galaxies in winds and how this material travels through the halo. Correlate these quantities to star formation in galaxies throughout cosmic history. Simulations reveal that a significant portion of every galaxy's evolution, particularly at high z, is dominated by bursts of SF, which are followed by powerful gusts of galactic outflow that sweep up a large fraction of gas in the ISM and send it through the circumgalactic medium. The dynamical effect of these outflows can significantly limit the amount of SF within the affected galaxy. At low z, however, sufficiently massive glaxies corresponding to L*-progenitors develop stable disks and switch into a continuous and quiescent mode of SF that does not drive outflows into the halo. Find inflow to be more continuous than outflow, although filamentary accretion onto the galaxy can be temporarily disrupted by recently ejected outflows. Using a variety of techniques, measure outflow rates and use them to derive mass-loading factors, and their dependence on circular velocity, halo mass, and stellar mass for a large sample of galaxies in the FIRE simulation suite, spanning four decades in halo mass, six decades in stellar mass, and a range of 4.0 > z > 0. Mass-loading factors for L*-progenitors are eta~=10 at high z, but decrease to eta<<1 at low z.
1501.03280
Solving the puzzle of subhalo spins
Wang, et al
Onions+ suggested, in Investigating the spin parameter distribution of subhaloes in two high resolution isolated halo simulations, that typical subhalo spins are consistently lower than the spin distribution found for field haloes. To further examine this puzzle, analyzed simulations of a cosmo volume with sufficient resolution to resolve a significant subhalo popualtion. Confirm the result of Onions+ and show that the typical spin of a subhalo decreases with decreasing mass and increasing proximity to the host halo center. Interpret this as the growing influence of tidal stripping in removing the outer layers, and hence the higher angular momentum particles, of the subhaloes as they move within the host potential. Investigating the z dependence of this effect, find that the typical subhalo spin is smaller with decreasing z. This indicates a temporal evolution as expected in the tidal stripping scenario.
Tuesday, January 13, 2015
Day 815
Tuesday, Wednesday.
1501.02798
Assembly bias & redshift-space distortions: impact on cluster dynamics tests of general relativity
Hearin
The RSD of galaxies surrounding massive clusters is emerging as a promising testbed for theories of modified gravity. Conventional applications of this method rely upon the assumption that the velocity field in the cluster environment is uniquely determined by the cluster mass profile. Yet, dark matter haloes in N-body simulations are known to violate the assumption that viral mass determines the configuration space distribution, an effect known as assembly bias. In this letter, show that assembly bias in simulated DM haloes also manifests in velocity space. In the 1-10 Mpc environment surrounding a cluster, a high-concentration "tracer" haloes exhibit a 10-20% larger pairwise-velocity dispersion profile relative to low-concentration tracer haloes of the same mass. This difference is comparable to the size of the RSD signal predicted by f(R) models designed to account for the cosmic acceleration. Use the age matching technique to study how color-selection effects may influence the cluster RSD signal, finding a ~10% effect due to refer satellites preferentially occupying higher mass haloes, and a ~5% effect due to assembly-biased colors of centrals. In order to use cluster RSD measurements to robustly constrain modified gravity, likely will need to develop empirical galaxy formation models more sophisticated than any in the current literature.
1501.02802
Characterization and correction of charge-induced pixel shifts in DECam
Gruen, Bernstein, Jarvis, Rowe, Vikram, Plazas, Seitz
Interaction of charges in CCDs with the already accumulated charge distribution causes both a flux dependence o the PSF (an increase of observed size with flux, also known as the brighter/fatter effect) and pixel-to-pixel correlations of the noise in flat fields. Describe these effects in the DECam with charge dependent shifts of effective pixel borders, i.e., the Antilogus+2014 model, which is then fit to measurements of flat-field noise correlations. The latter fall off approximately as a power-law r^-2.5 with pixel separation r, are isotropic except for an asymmetry in the direct neighbors along rows and columns, are stable in time, and are weakly dependent on wavelength. They show variations from chip to chip at the 20% level that correlate with the Si resistivity. The charge shifts predicted by the model cause biased shape measurements, primarily due to their effect on bright stars, at levels exceeding WL science requirements. Measure the flux dependence of star images and show that the effect can be mitigated by applying the reverse charge shifts at the pixel level during image processing. Differences in stellar size, however, remain significant due to residuals at larger distance from the centroid.
1501.03014
On the origin of intrinsic alignment in cosmic shear measurements: an analytic argument
Camelio, Lombardi
Galaxy IA can be a severe source of error in WL studies. The problem has been widely studied by numerical simulations and with heuristic models, but without a clear theoretical justification of its origin and amplitude. In particular, it is still unclear whether intrinsic alignment of galaxies is dominated by formation and accretion processes or by the effects of the instantaneous tidal field acting upon them. Investigate this question by developing a simple model of IA for elliptical galaxies, based on the instantaneous tidal field. Making use of the galaxy stellar distribution function, estimate the IA signal and find that although it has the expected dependence on the tidal field, it is too weak to account for the observed signal. This is an indirect validation of the standard view that IA is caused by formation and/or accretion processes.
1501.03119
Constraints and tensions in testing general relativity from Planck and CFHTLenS including intrinsic alignment systematics
Dossett, Ishak, Parkinson, Davis
Present constraints on GR at cosmo scales and the impact of IA in CFHTLenS on those constraints. Consider CMB T data from Planck, galaxy PS from WiggleZ, WL tomography from CFHTLenS, ISW-galaxy X-corrs, and BAO data from 6dF, SDSS DR7, and BOSS DR9. Use a parameterization of the MG that is binned in z and scale, a parameterization that evolves monotonically in scale but is binned in z, and a functional parameterization that evolves only in z. Present the results in terms of the MG parameters Q and Sigma. Employ an IA model with an amplitude A_CHFTLenS that is included in the parameter analysis. Find an improvement in the constraints on the MG parameters corresponding to 40-53% increase on the figure of merit compared to previous studies, and GR is found consistent with the data at the 95% CL. The bounds found on A_CFHTLenS are sensitive to whether the MG parameterization is scale dependent, and the correlations between A_CFHTLenS and MG parameters are found weak to moderate. A_CFHTLENS is found consistent with zero for the 3 MG parmeterizations and when the whole lensing sample is used. A significantly non-zero A_CFHTLenS for GR and the scale-independent MG parameterization is found when the optimized early-type galaxy sample of Heymans+2013 is used. Find that the tensions observed in previous studies persist, and there is an indication that CMB data and lensing data prefer different values for MG parameters, particularly for the parameter Sigma. The analysis of the confidence contours and probability distributions suggest that the bimodality found follows that of the known tension in the sigma_8 parameter.
1501.02798
Assembly bias & redshift-space distortions: impact on cluster dynamics tests of general relativity
Hearin
The RSD of galaxies surrounding massive clusters is emerging as a promising testbed for theories of modified gravity. Conventional applications of this method rely upon the assumption that the velocity field in the cluster environment is uniquely determined by the cluster mass profile. Yet, dark matter haloes in N-body simulations are known to violate the assumption that viral mass determines the configuration space distribution, an effect known as assembly bias. In this letter, show that assembly bias in simulated DM haloes also manifests in velocity space. In the 1-10 Mpc environment surrounding a cluster, a high-concentration "tracer" haloes exhibit a 10-20% larger pairwise-velocity dispersion profile relative to low-concentration tracer haloes of the same mass. This difference is comparable to the size of the RSD signal predicted by f(R) models designed to account for the cosmic acceleration. Use the age matching technique to study how color-selection effects may influence the cluster RSD signal, finding a ~10% effect due to refer satellites preferentially occupying higher mass haloes, and a ~5% effect due to assembly-biased colors of centrals. In order to use cluster RSD measurements to robustly constrain modified gravity, likely will need to develop empirical galaxy formation models more sophisticated than any in the current literature.
1501.02802
Characterization and correction of charge-induced pixel shifts in DECam
Gruen, Bernstein, Jarvis, Rowe, Vikram, Plazas, Seitz
Interaction of charges in CCDs with the already accumulated charge distribution causes both a flux dependence o the PSF (an increase of observed size with flux, also known as the brighter/fatter effect) and pixel-to-pixel correlations of the noise in flat fields. Describe these effects in the DECam with charge dependent shifts of effective pixel borders, i.e., the Antilogus+2014 model, which is then fit to measurements of flat-field noise correlations. The latter fall off approximately as a power-law r^-2.5 with pixel separation r, are isotropic except for an asymmetry in the direct neighbors along rows and columns, are stable in time, and are weakly dependent on wavelength. They show variations from chip to chip at the 20% level that correlate with the Si resistivity. The charge shifts predicted by the model cause biased shape measurements, primarily due to their effect on bright stars, at levels exceeding WL science requirements. Measure the flux dependence of star images and show that the effect can be mitigated by applying the reverse charge shifts at the pixel level during image processing. Differences in stellar size, however, remain significant due to residuals at larger distance from the centroid.
1501.03014
On the origin of intrinsic alignment in cosmic shear measurements: an analytic argument
Camelio, Lombardi
Galaxy IA can be a severe source of error in WL studies. The problem has been widely studied by numerical simulations and with heuristic models, but without a clear theoretical justification of its origin and amplitude. In particular, it is still unclear whether intrinsic alignment of galaxies is dominated by formation and accretion processes or by the effects of the instantaneous tidal field acting upon them. Investigate this question by developing a simple model of IA for elliptical galaxies, based on the instantaneous tidal field. Making use of the galaxy stellar distribution function, estimate the IA signal and find that although it has the expected dependence on the tidal field, it is too weak to account for the observed signal. This is an indirect validation of the standard view that IA is caused by formation and/or accretion processes.
1501.03119
Constraints and tensions in testing general relativity from Planck and CFHTLenS including intrinsic alignment systematics
Dossett, Ishak, Parkinson, Davis
Present constraints on GR at cosmo scales and the impact of IA in CFHTLenS on those constraints. Consider CMB T data from Planck, galaxy PS from WiggleZ, WL tomography from CFHTLenS, ISW-galaxy X-corrs, and BAO data from 6dF, SDSS DR7, and BOSS DR9. Use a parameterization of the MG that is binned in z and scale, a parameterization that evolves monotonically in scale but is binned in z, and a functional parameterization that evolves only in z. Present the results in terms of the MG parameters Q and Sigma. Employ an IA model with an amplitude A_CHFTLenS that is included in the parameter analysis. Find an improvement in the constraints on the MG parameters corresponding to 40-53% increase on the figure of merit compared to previous studies, and GR is found consistent with the data at the 95% CL. The bounds found on A_CFHTLenS are sensitive to whether the MG parameterization is scale dependent, and the correlations between A_CFHTLenS and MG parameters are found weak to moderate. A_CFHTLENS is found consistent with zero for the 3 MG parmeterizations and when the whole lensing sample is used. A significantly non-zero A_CFHTLenS for GR and the scale-independent MG parameterization is found when the optimized early-type galaxy sample of Heymans+2013 is used. Find that the tensions observed in previous studies persist, and there is an indication that CMB data and lensing data prefer different values for MG parameters, particularly for the parameter Sigma. The analysis of the confidence contours and probability distributions suggest that the bimodality found follows that of the known tension in the sigma_8 parameter.
Monday, January 12, 2015
Day 814
Monday. Tuesday.
1501.01960
How to bend galaxy disc profiles: the role of halo spin
Herpich et al
The radial density profiles of stellar galaxy disks can be well approximated as an exponential. Compared to this canonical form, however, the profiles in the majority of disc galaxies show downward or upward breaks at large radii. Currently, there is no coherent explanation in a galaxy formation context of the radial profiles per se, along with the two types of profiles breaks. Using a set of controlled hydrodynamic simulations of disc galaxy formation, find a correlation between the host halo's initial angular momentum and the resulting radial profile of the stellar disc: galaxies that live in haloes with a low spin parameter (lambda <~0.03 show an up-bending break in their disc density profiles, while galaxies in haloes of higher angular momentum show a down-bending break. Find that the case of pure exponential profiles (lambda ~0.035) coincides with the peak of the spin parameter distribution from cosmological simulations. The simulations not only imply an explanation of the observed behaviors, but also suggest that the physical original of this effect is related to the amount of radial redistribution of stellar mass, which is anti-correlated with lambda.
1401.01963
Green valley galaxies
Salim
The "green valley" is a wide region separating the blue and red peaks in the UV-opitcal color magnitude diagram, first revealed using GALEX UV photometry. They highlight the discriminating power of UV to very low relative levels of ongoing SF, to which the optical colors, including u-r, are insensitive. It corresponds to massive galaxies below the SF "main" sequence, and therefore represents a critical tool for the study of the quenching of SF and its possible resurgence in otherwise quiescent galaxies. This article reviews the results pertaining to morphology, structure, environment, dust content and gas properties of green valley galaxies in the local universe. Their relationship to AGN is also discussed. Attention is given to biases emerging from defining the "green valley" using optical colors. Review various evolutionary scenarios and present evidence for a new, quasi-static view of the green valley, in which the majority of galaxies currently in the green valley were only partially quenched in the distant past and now participate in a slow cosmic decline of SF, which also drives down the activity on the MS, presumably as a result of the dwindling accretion/cooling onto galaxy disks.
1501.01966
The stellar mass - halo mass relation for low mass X-ray groups at 0.5<z<1 in the CDFS with CSI
Patel et al
Since z~1, the stellar mass density locked in low mass groups and clusters has grown by a factor of ~8. Make statistical measurements of the stellar mass content of low mass X-ray groups at 0.5<z<1, enabling the calibration of stellar-to-halo mass scales for wide-field optical and IR surveys. Groups selected from Chandra and XMM-Newton observations of CDFS. Stellar mass computed using galaxies from Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey. Find no evidence for any significant evolution in the stellar-halo mass relation since z<1.
1501.01973
Satellite dwarf galaxies in a hierarchical universe: infall histories, group preprocessing, and reionization
Wetzel, Deason, Garrison-Kimmel
In the LG, almost all satellite dwarf galaxies that are within the viral radius of the MW and M31 exhibit strong environmental influence. The orbital histories of these satellite provide the key to understanding the role of the MW/M31 halo, lower mass groups, and cosmic reionization on the evolution of dwarf galaxies. Examine the viral-infall histories of satellites with M*=1e3-9 Msun using the ELVIS suite of cosmo zoom-in dissipation's simulations of 48 MW/M31-like haloes. Satellites at z=0 fell into the MW/M31 haloes typically 5-8 Gyr ago at z=0.5-1. However, they first fell into any host halo typically 7-10 Gyr ago at z=0.7-1.5. This difference arises because many satellites experienced "group preprocession" in another host halo, typically of Mvir~1e0-12 Msun, before falling into the MW/M31 haloes. Satellites with lower-mass and/or those closer to the MW/M31 fell in earlier and are more likely to have experienced group preprocessing; half of all satellites with M*<1e6 Msun were preprocessed in a group. Infalling groups also drive most satellite-satellite mergers within the MW/M31 haloes. Finally, none of the surviving satellites at z=0 were within the viral radius of their MW/M31 halo during reionization (z>6), and only <4% were satellites of any other host halo during reioinization. Thus, effects of cosmic reionization vs host-halo environment on the formation histories of surviving dwarf galaxies in the LG occurred at distance epochs and are separable in time.
1501.02047
Photometric redshift with bayesian priors on physical properties of galaxies
Tanaka
Preset a proof-of-concept analysis of photo-z with Bayesian priors on physical properties of galaxies. This concept is particularly suited for upcoming/on-going large imaging surveys, in which only several broad-band filters are available and it is hard to break some of the degeneracies in the multi-color space. Construct model templates of galaxies using a stellar population synthesis code and apply Bayesian priors on physical properties such as stellar mass and SFR. These priors are a function of redshift and they effectively evolve the templates with time in an observationally motivated way. Demonstrate that the priories help reduce the degeneracy and deliver significantly improved photometric redshifts. Furthermore, show that a template error function, which corrects for systematic flux errors in the model templates as a function of rest-frame wavelength, delivers further improvements. One great advantage of the technique is that they simultaneously measure z and physical properties of galaxies in a fully self-consistent manner, unlike the two-step measurements with different templates often performed. One may worry that the physical priors bias the inferred galaxy properties, but they show that the bias is smaller than systematic uncertainties inherent in physical properties inferred from the SED fitting and hence is not a major issue.e Extensively test and tune the priors in the on-going HSC survey and will make the code publicly available in the future.
1501.02055
Impact of baryonic processes on weak lensing cosmology: higher-order statistics and parameter bias
Osato, Shirasaki, Yoshida
Study the impact of baryonic physics on cosmological parameter estimation with WL surveys. Run a set of cosmo hydro sims with different galaxy formation models. Then perform ray-tracing simulations through the total matter density field to generate 100 independent convergence maps of 25 deg2 FoV, and use them to examine the ability of the following 3 lensing statistics as cosmological probes; PS, peak counts, and Minkowski Functionals. For the upcoming wide-field observations such as HSC survey with a sky coverage of 1400 deg2, the higher-order statistics provide tight constraints on the matter density, density fluctuation amplitude, and DE EoS, but appreciable parameter bias is induced by the baryonic processes such as gas cooling and stellar feedback. When PS, peak counts and MF are used, the relative bias in the DE EoS w is at the level of, (0.06, 0.5-0.6, and 0.01-0.1) sigma, respectively, where sigma is the overall error derived from Fisher analysis. Find the bias is induced in different directions in the parameter space depending on the statistics employed. While the 2pt statistics, i.e., PS, yield robust results against baryonic effects, the overall constraining power is weak compared with the other higher-order statistics. On the other hand, using higher-order statistics alone results in significantly biased parameter estimate. Suggest to use an optimized combination of, for example, PS and higher-order statistics so that the baryonic effects on parameter estimation are mitigated. Such 'calibrated' combination can place stringent and robust constraints on cosmological parameters.
1501.02251
On the origin of intracluster light in massive galaxy clusters
DeMaio, Gonzalez, Zabludoff, Zaritsky
The results of this pilot study are suggestive of a formation history of these clusters in which the ICL is built-up by the stripping of >0.2 L* galaxies, and disfavor significant contribution to the ICL by dwarf disruption or major mergers with the BCG.
1501.01960
How to bend galaxy disc profiles: the role of halo spin
Herpich et al
The radial density profiles of stellar galaxy disks can be well approximated as an exponential. Compared to this canonical form, however, the profiles in the majority of disc galaxies show downward or upward breaks at large radii. Currently, there is no coherent explanation in a galaxy formation context of the radial profiles per se, along with the two types of profiles breaks. Using a set of controlled hydrodynamic simulations of disc galaxy formation, find a correlation between the host halo's initial angular momentum and the resulting radial profile of the stellar disc: galaxies that live in haloes with a low spin parameter (lambda <~0.03 show an up-bending break in their disc density profiles, while galaxies in haloes of higher angular momentum show a down-bending break. Find that the case of pure exponential profiles (lambda ~0.035) coincides with the peak of the spin parameter distribution from cosmological simulations. The simulations not only imply an explanation of the observed behaviors, but also suggest that the physical original of this effect is related to the amount of radial redistribution of stellar mass, which is anti-correlated with lambda.
1401.01963
Green valley galaxies
Salim
The "green valley" is a wide region separating the blue and red peaks in the UV-opitcal color magnitude diagram, first revealed using GALEX UV photometry. They highlight the discriminating power of UV to very low relative levels of ongoing SF, to which the optical colors, including u-r, are insensitive. It corresponds to massive galaxies below the SF "main" sequence, and therefore represents a critical tool for the study of the quenching of SF and its possible resurgence in otherwise quiescent galaxies. This article reviews the results pertaining to morphology, structure, environment, dust content and gas properties of green valley galaxies in the local universe. Their relationship to AGN is also discussed. Attention is given to biases emerging from defining the "green valley" using optical colors. Review various evolutionary scenarios and present evidence for a new, quasi-static view of the green valley, in which the majority of galaxies currently in the green valley were only partially quenched in the distant past and now participate in a slow cosmic decline of SF, which also drives down the activity on the MS, presumably as a result of the dwindling accretion/cooling onto galaxy disks.
1501.01966
The stellar mass - halo mass relation for low mass X-ray groups at 0.5<z<1 in the CDFS with CSI
Patel et al
Since z~1, the stellar mass density locked in low mass groups and clusters has grown by a factor of ~8. Make statistical measurements of the stellar mass content of low mass X-ray groups at 0.5<z<1, enabling the calibration of stellar-to-halo mass scales for wide-field optical and IR surveys. Groups selected from Chandra and XMM-Newton observations of CDFS. Stellar mass computed using galaxies from Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey. Find no evidence for any significant evolution in the stellar-halo mass relation since z<1.
1501.01973
Satellite dwarf galaxies in a hierarchical universe: infall histories, group preprocessing, and reionization
Wetzel, Deason, Garrison-Kimmel
In the LG, almost all satellite dwarf galaxies that are within the viral radius of the MW and M31 exhibit strong environmental influence. The orbital histories of these satellite provide the key to understanding the role of the MW/M31 halo, lower mass groups, and cosmic reionization on the evolution of dwarf galaxies. Examine the viral-infall histories of satellites with M*=1e3-9 Msun using the ELVIS suite of cosmo zoom-in dissipation's simulations of 48 MW/M31-like haloes. Satellites at z=0 fell into the MW/M31 haloes typically 5-8 Gyr ago at z=0.5-1. However, they first fell into any host halo typically 7-10 Gyr ago at z=0.7-1.5. This difference arises because many satellites experienced "group preprocession" in another host halo, typically of Mvir~1e0-12 Msun, before falling into the MW/M31 haloes. Satellites with lower-mass and/or those closer to the MW/M31 fell in earlier and are more likely to have experienced group preprocessing; half of all satellites with M*<1e6 Msun were preprocessed in a group. Infalling groups also drive most satellite-satellite mergers within the MW/M31 haloes. Finally, none of the surviving satellites at z=0 were within the viral radius of their MW/M31 halo during reionization (z>6), and only <4% were satellites of any other host halo during reioinization. Thus, effects of cosmic reionization vs host-halo environment on the formation histories of surviving dwarf galaxies in the LG occurred at distance epochs and are separable in time.
1501.02047
Photometric redshift with bayesian priors on physical properties of galaxies
Tanaka
Preset a proof-of-concept analysis of photo-z with Bayesian priors on physical properties of galaxies. This concept is particularly suited for upcoming/on-going large imaging surveys, in which only several broad-band filters are available and it is hard to break some of the degeneracies in the multi-color space. Construct model templates of galaxies using a stellar population synthesis code and apply Bayesian priors on physical properties such as stellar mass and SFR. These priors are a function of redshift and they effectively evolve the templates with time in an observationally motivated way. Demonstrate that the priories help reduce the degeneracy and deliver significantly improved photometric redshifts. Furthermore, show that a template error function, which corrects for systematic flux errors in the model templates as a function of rest-frame wavelength, delivers further improvements. One great advantage of the technique is that they simultaneously measure z and physical properties of galaxies in a fully self-consistent manner, unlike the two-step measurements with different templates often performed. One may worry that the physical priors bias the inferred galaxy properties, but they show that the bias is smaller than systematic uncertainties inherent in physical properties inferred from the SED fitting and hence is not a major issue.e Extensively test and tune the priors in the on-going HSC survey and will make the code publicly available in the future.
1501.02055
Impact of baryonic processes on weak lensing cosmology: higher-order statistics and parameter bias
Osato, Shirasaki, Yoshida
Study the impact of baryonic physics on cosmological parameter estimation with WL surveys. Run a set of cosmo hydro sims with different galaxy formation models. Then perform ray-tracing simulations through the total matter density field to generate 100 independent convergence maps of 25 deg2 FoV, and use them to examine the ability of the following 3 lensing statistics as cosmological probes; PS, peak counts, and Minkowski Functionals. For the upcoming wide-field observations such as HSC survey with a sky coverage of 1400 deg2, the higher-order statistics provide tight constraints on the matter density, density fluctuation amplitude, and DE EoS, but appreciable parameter bias is induced by the baryonic processes such as gas cooling and stellar feedback. When PS, peak counts and MF are used, the relative bias in the DE EoS w is at the level of, (0.06, 0.5-0.6, and 0.01-0.1) sigma, respectively, where sigma is the overall error derived from Fisher analysis. Find the bias is induced in different directions in the parameter space depending on the statistics employed. While the 2pt statistics, i.e., PS, yield robust results against baryonic effects, the overall constraining power is weak compared with the other higher-order statistics. On the other hand, using higher-order statistics alone results in significantly biased parameter estimate. Suggest to use an optimized combination of, for example, PS and higher-order statistics so that the baryonic effects on parameter estimation are mitigated. Such 'calibrated' combination can place stringent and robust constraints on cosmological parameters.
1501.02251
On the origin of intracluster light in massive galaxy clusters
DeMaio, Gonzalez, Zabludoff, Zaritsky
The results of this pilot study are suggestive of a formation history of these clusters in which the ICL is built-up by the stripping of >0.2 L* galaxies, and disfavor significant contribution to the ICL by dwarf disruption or major mergers with the BCG.
Thursday, January 8, 2015
Day 813
Friday.
1501.01632
Cosmic variance of the galaxy cluster weak lensing signal
Gruen, Seitz, et al
Intrinsic variations of the projected density profiles of clusters of galaxies at fixed mass are a source of uncertainty for cluster weak lensing. Present a semi-analytical model to account for this effect, based on a combination of variations in halo concentration, ellipticity and orientation, and the presence of correlated haloes. Calibrate the parameters of the model at the 10% level to match the empirical cosmic variance of cluster profiles at M200m=1e14-15 Msun/h, z=0.25~0.5 in a cosmological simulation. Show that WL measurements of clusters provide correct mass likelihoods. Effects on the achievable accuracy of WL cluster mass measurements are particularly strong for the most massive clusters and deep observations (with ~20% uncertainty from cosmic variance alone at M200m=1e15 Msun/h and 0.25), but significant also under typical ground-based conditions. Show that neglecting intrinsic profile variations leads to biases in the mass-observable relation constrained with WL, both for intrinsic scatter and overall scale (the latter at the 15% level). These biases are in excess of the statistical errors of upcoming surveys and can be avoided if the cosmic variance of cluster profiles is accounted for.
1501.01632
Cosmic variance of the galaxy cluster weak lensing signal
Gruen, Seitz, et al
Intrinsic variations of the projected density profiles of clusters of galaxies at fixed mass are a source of uncertainty for cluster weak lensing. Present a semi-analytical model to account for this effect, based on a combination of variations in halo concentration, ellipticity and orientation, and the presence of correlated haloes. Calibrate the parameters of the model at the 10% level to match the empirical cosmic variance of cluster profiles at M200m=1e14-15 Msun/h, z=0.25~0.5 in a cosmological simulation. Show that WL measurements of clusters provide correct mass likelihoods. Effects on the achievable accuracy of WL cluster mass measurements are particularly strong for the most massive clusters and deep observations (with ~20% uncertainty from cosmic variance alone at M200m=1e15 Msun/h and 0.25), but significant also under typical ground-based conditions. Show that neglecting intrinsic profile variations leads to biases in the mass-observable relation constrained with WL, both for intrinsic scatter and overall scale (the latter at the 15% level). These biases are in excess of the statistical errors of upcoming surveys and can be avoided if the cosmic variance of cluster profiles is accounted for.
Wednesday, January 7, 2015
Day 812
Thursday.
1410.5423
Glow in the dark matter: observing galactic haloes with scattered light
Davis, Silk
Constrain upper limit on the DM-photon cross section using the Dragonfly instrument, by considering the observation of diffuse haloes of light around the disks of spiral galaxies.
1410.5631
Data driven discovery in astrophysics
Longo et al
Describe some of the recent examples of machine learning tool applications on big data.
1501.01306
Understanding the cosmic web
Cautun et al
At early times the cosmic is dominated by tenuous filaments and sheets, which, during subsequent evolution, merge together, such that the present day web is dominated by fewer, but much more massive, structures. Also show that voids are more naturally described in terms of their boundaries and not their centers. Illustrate this for void density profiles, which, when expressed as function of the distance from void boundary, show a universal profile in good qualitative agreement with the theoretical shell-crossing framework of expanding underdense regions.
1501.01398
Can we measure galaxy environments with photometric redshifts?
Lai, ... Merson, Baugh, et al
Quantify how the density measured with the nearest neighbor approach is affected by photo-z uncertainties by using the Durham mock catalogs, in which the 3D real-space environments and the properties of galaxies are exactly known. Furthermore, present an optimization scheme in the choice of parameters used in the 2D projected measurement which yields the tightest correlation with respect to the 3D real-space environments. By adopting the parameters in the density measurements, show that the correlation between the 2D projected optimized density and real-space density can still be revealed, and the color-density relation is also visible even for a photo-z uncertainty up to sigma[Delta_z/(1+z)] = 0.06. Find that a deep (i~25) photometric z survey with sigma[Delta_z/(1+z)]=0.02 yields a comparable performance of density measurement to a shallower i~22.5 (24.1) spectroscopic sample with 40%(20%) sampling rate. Finally, discuss the application of the local density measurements to the Pan-STARRS Medium Deep survey, one of the largest on-going deep imaging surveys. Using data from ~5deg^2 of survey area, results show that it is possible to measure local density and to probe the color-density relation in the PS-MDS, confirming the simulation results. The color-density relation, however, quickly degrades for data covering smaller areas.
1501.01487
Tests for the expansion of the Universe
Lopez-Corredoira
Review some independent cosmo tests of the expansion of the universe: CMB temperature vs z, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczy'nski test. Some tests favor expansion and others favor a static Universe. Almost all tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, and evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.
1410.5423
Glow in the dark matter: observing galactic haloes with scattered light
Davis, Silk
Constrain upper limit on the DM-photon cross section using the Dragonfly instrument, by considering the observation of diffuse haloes of light around the disks of spiral galaxies.
1410.5631
Data driven discovery in astrophysics
Longo et al
Describe some of the recent examples of machine learning tool applications on big data.
1501.01306
Understanding the cosmic web
Cautun et al
At early times the cosmic is dominated by tenuous filaments and sheets, which, during subsequent evolution, merge together, such that the present day web is dominated by fewer, but much more massive, structures. Also show that voids are more naturally described in terms of their boundaries and not their centers. Illustrate this for void density profiles, which, when expressed as function of the distance from void boundary, show a universal profile in good qualitative agreement with the theoretical shell-crossing framework of expanding underdense regions.
1501.01398
Can we measure galaxy environments with photometric redshifts?
Lai, ... Merson, Baugh, et al
Quantify how the density measured with the nearest neighbor approach is affected by photo-z uncertainties by using the Durham mock catalogs, in which the 3D real-space environments and the properties of galaxies are exactly known. Furthermore, present an optimization scheme in the choice of parameters used in the 2D projected measurement which yields the tightest correlation with respect to the 3D real-space environments. By adopting the parameters in the density measurements, show that the correlation between the 2D projected optimized density and real-space density can still be revealed, and the color-density relation is also visible even for a photo-z uncertainty up to sigma[Delta_z/(1+z)] = 0.06. Find that a deep (i~25) photometric z survey with sigma[Delta_z/(1+z)]=0.02 yields a comparable performance of density measurement to a shallower i~22.5 (24.1) spectroscopic sample with 40%(20%) sampling rate. Finally, discuss the application of the local density measurements to the Pan-STARRS Medium Deep survey, one of the largest on-going deep imaging surveys. Using data from ~5deg^2 of survey area, results show that it is possible to measure local density and to probe the color-density relation in the PS-MDS, confirming the simulation results. The color-density relation, however, quickly degrades for data covering smaller areas.
1501.01487
Tests for the expansion of the Universe
Lopez-Corredoira
Review some independent cosmo tests of the expansion of the universe: CMB temperature vs z, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczy'nski test. Some tests favor expansion and others favor a static Universe. Almost all tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, and evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.
Monday, January 5, 2015
Day 811
Wednesday.
1412.6501
Confirmation of a star formation bias in type Ia supernova distances and its effect on measurement of the Hubble Constant
Rigault, et al
Previously, used the Nearby Supernova Factory sample to show that SNeIa having locally SF environments are dimmer than SNeIa having locally passive environments. Here, use the constitution sample together with host galaxy data from GALEX to independently confirm that result. The effect is seen using both the SALT2 and MLCS2k2 light curve fitting and standardization methods, with brightness differences of 0.094pm0.037 mag for SALT2 and 0.155pm0.041 mag for MLCS2k2 with R_V=2.5 When combined with previous measurement the effect is 0.094pm0.037 mag for SALT2. If the ratio of these local SNIa environments changes with redshift or sample selection, this can lead to a bias in cosmological measurements. Explore this issue further, using as an example the direct measurement of H0. GALEX observations show that the SNeIa having standardized absolute magnitudes calibrated via the Cepheid period-luminosity relation using HST originate in predominantly SF environments, where as only ~50% of the Hubble flow comparison sample have locally SF environments. As a consequence, the H0 measurement using SNeIa is currently overestimated. Correcting for this bias, find a value of H0^corr=70.6pm2.6 km/s/Mpc when using the LMC distance, MW parallaxes and the NGC4258 megamaser as the Cepheid zero point, and 68.8pm3.3km/s/Mpc when only using NGC4258. The correction brings the direct measurement of N0 within 1sigma of recent indirect measurements based on the CMB PS.
1501.00996
Using atomic clocks to detect gravitational waves
Loeb, Maoz
Atomic clocks have recently reached a rational timing precision of <1e-18. Point out that an array of atomic clocks, distributed along the Earth's orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz GWs, such as those emitted by SMBH binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, cruelty envisioned for the eLISA mission.
1501.01002
The first galaxies: simulating their feedback-regulated assembly
Jeon, et al
Investigate the formation of a galaxy reaching a virial mass of 1e8 at z~10 by carrying out a zoomed radiation-hydrodynamical cosmo sim. This sim traces Pop III SF, characterized by a modestly top-heavy IMF, and considers stellar feedback such as photoionization heating from Pop III and Pop II stars, mechanical and chemical feedback from SNe, and X-ray feedback from accreting BHs and high-mass X-ray binaries. Self-consistently impose a transition in SF mode from top-heavy Pop III to low-mass Pop II at the critical metallicity Zcrit=1e-3.5 Zsun. Find that the SFR in the computational box is dominated by Pop III until z~13, and by Pop II thereafter. The IGM is metal-enriched to an average of Zavg=1e-4 Zsun at z~10, mainly by pair-instability SNe, while 70% of the produced Pop II stars die in core-collapse SNe. The simulated galaxy experiences bursty SF, with a substantially reduced gas content due to photoionization heating form Pop III and Pop II stars, together with SN feedback. Specifically, this gives rise to a baryon fraction of fbar=0.05 at z~10. All the gas within the simulated galaxy is metal-enriched above 1e-5 Zsun, such that there are no remaining pockets of primordial gas. Further estimate the intrinsic luminosity of the simulated galaxy to be Lbol~5e6 Lsun, corresponding to an observed flux of 1e-3 nJy, which is too low to be detected by the JWST. Also show that the simulated galaxy falls below the observed relation between mean stellar metallicity and total stellar mass for local dwarf galaxies by ~1 dex, although this may be an artifact of having missed any subsequent SF at z<10.
1501.01048
The SKA as a doorway to angular momentum
Obreschkow et al
The SKA has a unique opportunity to become the world-leading facility for angular momentum studies due to its ability to measure the resolved and/or global HI kinematics in very large and well-characterised galaxy samples.
1412.6501
Confirmation of a star formation bias in type Ia supernova distances and its effect on measurement of the Hubble Constant
Rigault, et al
Previously, used the Nearby Supernova Factory sample to show that SNeIa having locally SF environments are dimmer than SNeIa having locally passive environments. Here, use the constitution sample together with host galaxy data from GALEX to independently confirm that result. The effect is seen using both the SALT2 and MLCS2k2 light curve fitting and standardization methods, with brightness differences of 0.094pm0.037 mag for SALT2 and 0.155pm0.041 mag for MLCS2k2 with R_V=2.5 When combined with previous measurement the effect is 0.094pm0.037 mag for SALT2. If the ratio of these local SNIa environments changes with redshift or sample selection, this can lead to a bias in cosmological measurements. Explore this issue further, using as an example the direct measurement of H0. GALEX observations show that the SNeIa having standardized absolute magnitudes calibrated via the Cepheid period-luminosity relation using HST originate in predominantly SF environments, where as only ~50% of the Hubble flow comparison sample have locally SF environments. As a consequence, the H0 measurement using SNeIa is currently overestimated. Correcting for this bias, find a value of H0^corr=70.6pm2.6 km/s/Mpc when using the LMC distance, MW parallaxes and the NGC4258 megamaser as the Cepheid zero point, and 68.8pm3.3km/s/Mpc when only using NGC4258. The correction brings the direct measurement of N0 within 1sigma of recent indirect measurements based on the CMB PS.
1501.00996
Using atomic clocks to detect gravitational waves
Loeb, Maoz
Atomic clocks have recently reached a rational timing precision of <1e-18. Point out that an array of atomic clocks, distributed along the Earth's orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz GWs, such as those emitted by SMBH binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, cruelty envisioned for the eLISA mission.
1501.01002
The first galaxies: simulating their feedback-regulated assembly
Jeon, et al
Investigate the formation of a galaxy reaching a virial mass of 1e8 at z~10 by carrying out a zoomed radiation-hydrodynamical cosmo sim. This sim traces Pop III SF, characterized by a modestly top-heavy IMF, and considers stellar feedback such as photoionization heating from Pop III and Pop II stars, mechanical and chemical feedback from SNe, and X-ray feedback from accreting BHs and high-mass X-ray binaries. Self-consistently impose a transition in SF mode from top-heavy Pop III to low-mass Pop II at the critical metallicity Zcrit=1e-3.5 Zsun. Find that the SFR in the computational box is dominated by Pop III until z~13, and by Pop II thereafter. The IGM is metal-enriched to an average of Zavg=1e-4 Zsun at z~10, mainly by pair-instability SNe, while 70% of the produced Pop II stars die in core-collapse SNe. The simulated galaxy experiences bursty SF, with a substantially reduced gas content due to photoionization heating form Pop III and Pop II stars, together with SN feedback. Specifically, this gives rise to a baryon fraction of fbar=0.05 at z~10. All the gas within the simulated galaxy is metal-enriched above 1e-5 Zsun, such that there are no remaining pockets of primordial gas. Further estimate the intrinsic luminosity of the simulated galaxy to be Lbol~5e6 Lsun, corresponding to an observed flux of 1e-3 nJy, which is too low to be detected by the JWST. Also show that the simulated galaxy falls below the observed relation between mean stellar metallicity and total stellar mass for local dwarf galaxies by ~1 dex, although this may be an artifact of having missed any subsequent SF at z<10.
1501.01048
The SKA as a doorway to angular momentum
Obreschkow et al
The SKA has a unique opportunity to become the world-leading facility for angular momentum studies due to its ability to measure the resolved and/or global HI kinematics in very large and well-characterised galaxy samples.
Day 810
Tuesday.
1501.00500
When did round disk galaxies form?
Takeuchi et al
When and how galaxy morphology such as disk and bulge seen in the present-day universe emerged is still not clear. In the universe at z>2, galaxies with various morphology are seen, and SF galaxies at z~2 show an intrinsic shape of bar-like structure. Then when did round disk structure form? Take a simple and straightforward approach to see the epoch when the round disk galaxy population emerged, by constraining the intrinsic shape statistically based on apparent axial ratio distribution of galaxies. Derived the distributions of the apparent axial ratios in the rest-frame optical light (~5000 A) of SF main sequence galaxies at 2.5>z>1.4, 1.4>z>0.85, and 0.85>z>0.5, and found that the apparent axial ratios of them show peaky distributions at z>0.85, while a rather flat distribution at the lower redshift. By using a triaxial model for the intrinsic shape (A>B>C), find the best-fit models give the peaks of the B/A distribution of 0.81pm0.04, 0.84pm0.04, and 0.92pm0.05 at 2.5>z>1.4, 1.4>z>0.85, and 0.85>z>0.5, respectively. The last value is close to the local value of 0.95. Thickness (C/A) is ~0.25 at all the z and is close to the local value (0.21). The results indicate the shape of the SF galaxies in the MS changes gradually, and the round disk is established at around z~0.9. Establishment of the round disk may be due to a cease of violent interaction of galaxies or a growth of a bulge and/or a super-massive BH resides at the center of a galaxy which dissolves the bar structure.
1501.00690
Galactic magnetic fields and hierarchical galaxy formation
Rodrigues, ... Baugh, et al
A framework is introduced for coupling the evolution of galactic magnetic fields sustained by the mean-field dynamo with the formation and evolution of galaxies in the cold dark matter cosmology. Estimates of the steady-state strength of the large-scale and turbulence B-fields from mean-field and fluctuation dynamo models are used together with galaxy properties predicted by SAM of galaxy formation for a population of spiral galaxies. Find that the field strength is mostly controlled by the evolving gas content of the galaxies. Thus, because of the differences in the implementation of the SF law, feedback from SNe and ram-pressure stripping, each of the galaxy formation models considered predicts a distribution of field strengths with unique features. The most prominent of them is the difference in typical B-fields strengths obtained for the satellite and central galaxies populations as well as the typical strength of the large-scale B-field in galaxies of different mass.
1501.00963
The eleventh and twelfth data releases of the Sloan Digital Sky Survey: final data from SDSS-III
Alam et al
SDSS-III: data from 2008 to 2014. Lots of data.
1410.4345
HOPE: a Python Just-In_time compiler for astrophysical computations
Akeret, Gamper, Amara, Refregier
In order to combine the ease of Python and the speed of C++, developed HOPE, a specialized Python just-in-time (JIT) compiler designed for numerical astrophysical applications. HOPE focuses on a subset of the language and is able to translate Python code into C++ while performing numerical optimisation on mathematical expressions at runtime. To enable the JIT compilation, the user only needs to adda a decorator to the function definition. Assess the performance of HOPE by performing a series of benchmarks and compare its execution speed with that of plain Python, C++ and the other existing frameworks. Find that HOPE improves the performance compared to plain Python by a factor of 2 to 120, achieves speeds comparable to that of C++ and often exceeds the speed of the existing solutions. Discuss the differences between HOPE and the other frameworks, as well as future extensions of its capabilities. The fully documented HOPE packages is available on the web.
1501.00500
When did round disk galaxies form?
Takeuchi et al
When and how galaxy morphology such as disk and bulge seen in the present-day universe emerged is still not clear. In the universe at z>2, galaxies with various morphology are seen, and SF galaxies at z~2 show an intrinsic shape of bar-like structure. Then when did round disk structure form? Take a simple and straightforward approach to see the epoch when the round disk galaxy population emerged, by constraining the intrinsic shape statistically based on apparent axial ratio distribution of galaxies. Derived the distributions of the apparent axial ratios in the rest-frame optical light (~5000 A) of SF main sequence galaxies at 2.5>z>1.4, 1.4>z>0.85, and 0.85>z>0.5, and found that the apparent axial ratios of them show peaky distributions at z>0.85, while a rather flat distribution at the lower redshift. By using a triaxial model for the intrinsic shape (A>B>C), find the best-fit models give the peaks of the B/A distribution of 0.81pm0.04, 0.84pm0.04, and 0.92pm0.05 at 2.5>z>1.4, 1.4>z>0.85, and 0.85>z>0.5, respectively. The last value is close to the local value of 0.95. Thickness (C/A) is ~0.25 at all the z and is close to the local value (0.21). The results indicate the shape of the SF galaxies in the MS changes gradually, and the round disk is established at around z~0.9. Establishment of the round disk may be due to a cease of violent interaction of galaxies or a growth of a bulge and/or a super-massive BH resides at the center of a galaxy which dissolves the bar structure.
1501.00690
Galactic magnetic fields and hierarchical galaxy formation
Rodrigues, ... Baugh, et al
A framework is introduced for coupling the evolution of galactic magnetic fields sustained by the mean-field dynamo with the formation and evolution of galaxies in the cold dark matter cosmology. Estimates of the steady-state strength of the large-scale and turbulence B-fields from mean-field and fluctuation dynamo models are used together with galaxy properties predicted by SAM of galaxy formation for a population of spiral galaxies. Find that the field strength is mostly controlled by the evolving gas content of the galaxies. Thus, because of the differences in the implementation of the SF law, feedback from SNe and ram-pressure stripping, each of the galaxy formation models considered predicts a distribution of field strengths with unique features. The most prominent of them is the difference in typical B-fields strengths obtained for the satellite and central galaxies populations as well as the typical strength of the large-scale B-field in galaxies of different mass.
1501.00963
The eleventh and twelfth data releases of the Sloan Digital Sky Survey: final data from SDSS-III
Alam et al
SDSS-III: data from 2008 to 2014. Lots of data.
1410.4345
HOPE: a Python Just-In_time compiler for astrophysical computations
Akeret, Gamper, Amara, Refregier
In order to combine the ease of Python and the speed of C++, developed HOPE, a specialized Python just-in-time (JIT) compiler designed for numerical astrophysical applications. HOPE focuses on a subset of the language and is able to translate Python code into C++ while performing numerical optimisation on mathematical expressions at runtime. To enable the JIT compilation, the user only needs to adda a decorator to the function definition. Assess the performance of HOPE by performing a series of benchmarks and compare its execution speed with that of plain Python, C++ and the other existing frameworks. Find that HOPE improves the performance compared to plain Python by a factor of 2 to 120, achieves speeds comparable to that of C++ and often exceeds the speed of the existing solutions. Discuss the differences between HOPE and the other frameworks, as well as future extensions of its capabilities. The fully documented HOPE packages is available on the web.
Day 809
Wednesday.
1412.7757
Constraints on changes in the proton-electron mass ratio using methanol lines
Kanekar et al
Find no evidence for changes in the proton-electron mass ratio over a lookback time of ~7.5 Gyrs (0<z<0.885).
1412.7768
Multi-stream portrait of the cosmic web
Ramachandra, Shandarin
At the resolution of the simulation (i.e. without additional smoothing) the cosmic web represents a hierarchical structure: each halo is embedded in the filamentary framework of the web at the filament crossings, and each filament is embedded in the wall like fabric of the web at the wall crossings. Locally, the haloes are the regions of highest number of streams, the number of streams in the neighboring filaments is higher than in the neighboring walls, and walls are regions where number of steams is greater or equal to three. Voids are uniquely defined by the local conditions requiring to be a single-stream flow region. The shells of streams around halos are quite thin and the closest void region is typically within roughly one and a half of FOF radii of the halo.
1412.7823
Baryon content of massive galaxy clusters (0.57<z<1.33)
Chiu, Mohr, et al
Study the stellar, BCG and ICM masses of 14 SPT selected galaxy clusters with median redshift z=0.9 and median mass M500=6e14 Msun. Estimate stellar masses for each cluster and BCG using 6 photometric bands spanning the range from the UV to the NIR observed with VLT, HST and Spitzer. The ICM masses are derived from Chandra and XMM-Newton X-ray observatories, and the viral masses are derived form the SPT SZ effect signatures. At z=0.9 the BCG mass M*_BCG constitutes 0.12% of the halo mass for a 6e14 Msun cluster, and this fraction falls as M500^-0.58pm0.07. The cluster stellar MF has a characteristic mass M0=1e11Msun, and the number of galaxies per unit mass in clusters is larger than in the field by a factor 1.6pm0.2. Both results are consistent with measurements on group scales and at lower redshift. Combine the SPT sample with previously published samples at low redshift that we correct to a common initial MF and for systematic differences in viral masses. Then explore mass and z trends in the stellar fraction f_star, the ICM fraction f_ICM, the cold baryon fraction f_c and the baryon fraction f_b. At a pivot mass of 6e14 Msun and z=0.9, the characteristic values are f_star=1.1pm0.1%, f_ICM=9.6pm0.5%, f_c=10.4pm1.2% and f_b=10.7pm0.6%. These fraction all vary with cluster mass at high significance, indicating that higher mass clusters have lower f_star and f_c and higher f_ICM and f_b. When accounting for a 15% systematic viral mass uncertainty, there is no statistically significant redshift trend at fixed mass in these baryon fractions.
1412.7757
Constraints on changes in the proton-electron mass ratio using methanol lines
Kanekar et al
Find no evidence for changes in the proton-electron mass ratio over a lookback time of ~7.5 Gyrs (0<z<0.885).
1412.7768
Multi-stream portrait of the cosmic web
Ramachandra, Shandarin
At the resolution of the simulation (i.e. without additional smoothing) the cosmic web represents a hierarchical structure: each halo is embedded in the filamentary framework of the web at the filament crossings, and each filament is embedded in the wall like fabric of the web at the wall crossings. Locally, the haloes are the regions of highest number of streams, the number of streams in the neighboring filaments is higher than in the neighboring walls, and walls are regions where number of steams is greater or equal to three. Voids are uniquely defined by the local conditions requiring to be a single-stream flow region. The shells of streams around halos are quite thin and the closest void region is typically within roughly one and a half of FOF radii of the halo.
1412.7823
Baryon content of massive galaxy clusters (0.57<z<1.33)
Chiu, Mohr, et al
Study the stellar, BCG and ICM masses of 14 SPT selected galaxy clusters with median redshift z=0.9 and median mass M500=6e14 Msun. Estimate stellar masses for each cluster and BCG using 6 photometric bands spanning the range from the UV to the NIR observed with VLT, HST and Spitzer. The ICM masses are derived from Chandra and XMM-Newton X-ray observatories, and the viral masses are derived form the SPT SZ effect signatures. At z=0.9 the BCG mass M*_BCG constitutes 0.12% of the halo mass for a 6e14 Msun cluster, and this fraction falls as M500^-0.58pm0.07. The cluster stellar MF has a characteristic mass M0=1e11Msun, and the number of galaxies per unit mass in clusters is larger than in the field by a factor 1.6pm0.2. Both results are consistent with measurements on group scales and at lower redshift. Combine the SPT sample with previously published samples at low redshift that we correct to a common initial MF and for systematic differences in viral masses. Then explore mass and z trends in the stellar fraction f_star, the ICM fraction f_ICM, the cold baryon fraction f_c and the baryon fraction f_b. At a pivot mass of 6e14 Msun and z=0.9, the characteristic values are f_star=1.1pm0.1%, f_ICM=9.6pm0.5%, f_c=10.4pm1.2% and f_b=10.7pm0.6%. These fraction all vary with cluster mass at high significance, indicating that higher mass clusters have lower f_star and f_c and higher f_ICM and f_b. When accounting for a 15% systematic viral mass uncertainty, there is no statistically significant redshift trend at fixed mass in these baryon fractions.
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