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1503.00722
The role of bulge formation in the homogenization of stellar populations at $z\sim2$ as revealed by internal color dispersion in CANDELS
Boada, ... Koekemoer, Koo, Grogin, et al
Use data from the CANDELS to study how the spatial variation in the stellar populations of galaxies relate to the formation of galaxies at 1.5<z<3.5. Use the internal color dispersion (ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with Sersic indices <2) and stellar masses between 10<Log(M/Msun)<11. There is a marked decrease the ICD as the stellar mass and/or the Sersic index increases. By studying the relations between the ICD and other galaxy properties including sizes, total colors, SFR, and dust attenuation, conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high SF clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, 10<(log M/Msun)<11, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses, and/or higher Sersic index (n>2) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have both a quiescent bulge along with a SF disk, typical of Hubble Sequence galaxies, this is most common for stellar masses 10<log M/Msun<11 and when the bulge component remains relatively small (n<2).
1503.00731
Dark matter halo models of stellar mass-dependent galaxy clustering in PRIMUS+DEEP2 at 0.2<z<1.2
Skibba, Coil, ... et al
Utilize LCDM halo occupation models of galaxy clustering to investigate the evolving stellar mass dependent clustering of galaxies in PRIMUS and DEEP2 over the past eight billion years of cosmic time, between 0.2<z<1.2. These clustering measurements provide new constraints on the connections between dark matter halo properties and galaxy properties in the context of the evolving large-scale structure of the universe. Using both an analytic model and a set of mock galaxy catalogs, find a strong correlation between central galaxy stellar mass and DM halo mass over the range M_halo~1e11-13 Msun/h, approximately consistent with previous observations and theoretical predictions. The stellar-to-halo mass relation (SHMR) and the mass scale where SF efficiency reaches a maximum appear to evolve more strongly than predicted by other models. Find that the fraction of satellite galaxies in haloes of a given mass decreases by ~5% from z~0.5 to 0.9, and find that the M1/Mmin ratio, which quantifies the critical mass above which haloes host at least one satellite, decreases from ~20 at z~0 to ~13 at z~0.9. Considering the evolution of the sub halo mass function vis-a-vis satellite abundances, this trend has implications for relations between satellite galaxies and halo substructures and for intracluster mass, which we argue has grown due to stripped and disrupted satellites between z~0.9 and 0.5.
1503.00734
Hydrogen reionization in the Illustris Universe
Bauer Springel, Vogelsberger, Genel, Torrey, Sijacki, Nelson, Hernquist
Hydro-sims of galaxy formation such as the Illustris simulations have progressed to a state where they approximately reproduce the observed stellar mass function from high to low z. This in principle allows self-consistent models of reionization that exploit the accurate representation of the diffuse gas distribution together with the realistic growth of galaxies provided by these simulations, within a representative cosmo volume. In this work, apply and compare two radiative transfer algorithms implemented in a GPU-accelerated code to the 106.5 Mpc wide volume of Illustris in post processing in order to investigate the reionization transition predicted by this model. Find that the first generation of galaxies formed by Illustris is just about able to reionize the universe by z~7, provided quite optimistic assumptions about the escape fraction and the resolution limitations are made. The most optimistic model finds an optical depth of tau~0.065, which is in very good agreement with recent Planck 2015 determinations. Furthermore, show that moment-based approaches for radiative transfer with the M1 closure give broadly consistent results with the angular-resolved radiative transfer scheme as far as the global reionization history is concerned. Also confirm earlier findings that the reduced speed-of-light approximation introduces non-negligible inaccuracies. In the favored fiducial model, 20% of the hydrogen is reionized by z=9.20, and this rapidly climbs to 80% by z=6.92. I then takes until z=6.24 before 99% of the H is ionized. On average, reionization proceeds 'inside-out' in the models, with a size distribution of reionzed bubbles that progressively features regions of ever larger size who the abundance of small bubbles stays fairly constant.
1503.00755
Star formation in semi-analytic galaxy formation models with multiphase gas
Somerville, Popping, Trager
Implement physically motivated recipes for partitioning cold gas into different phases (atomic, molecular, and ionized) in galaxies within SAM of galaxy formation based on cosmo merger trees. Then model the conversion of molecular gas into stars using empirical recipes motivated by recent observations. Explore the impact of these new recipes on the evolution of fundamental galaxy properties such as stellar mass, SFR, and gas and stellar phase metallicity. Present predictions for stellar MF, stellar mass vs SFR relations, and cold gas phase and stellar phase metallicity relations for the fiducial models, from z~6 to the present day. In addition, present predictions for the global SFR, mass assembly history, and cosmic enrichment history. Find that the predicted stellar properties of galaxies (stellar mass, SFR, metallicity) are remarkably insensitive to the details of the recipes used for partitioning gas into HI and H2. See significant sensitivity to the recipes for H2 formation only in very low mass halos, which host galaxies that are not detectable with current observational facilitates except very nearby. The properties of low-mass galaxies are also quite insensitive to the details of the recipe used for converting H2 into stars, while the formation epoch of massive galaxies does depend on this significantly.
1503.00975
A derivation of masses and total luminosities of galaxy groups and clusters in the maxBCG catalogue
Proctor, et al
Report the results of a multi-waveband analysis of the masses and luminosities of ~600 galaxy groups and clusters identified in the maxBCG catalogue. These data are intended to form the basis of future work on the formation of the "m_12 gap" in galaxy groups and clusters. Use SDSS spectroscopy and gri band photometry to estimate galaxy group/cluster viral radii, masses and total luminosities. In order to establish the robustness of the results, compare them with literature studies that utilize a variety of mass determinations techniques (dynamic, X-ray, WL) and total luminosities estimated in the Bri and K wavebands. Also compare results to predictions derived from the Millennium Sim. Find that, once selection effects are properly accounted for, excellent agreement exists between the results and the literature with the exception of a single observations study. Also find that the Millennium Sim does an excellent job of predicting the effects of the selection criteria. Results show that, over the mass range ~1e13-15 Msun, variations in the slope of the mass-luminosity scaling relation with mass detected in this and many other literature studies is in part the result of selection effects. Show that this can have serious ramifications on attempts to determine how the mass-to-light ratio of galaxy groups and cluster varies with mass.
1503.01113
I. Apples stop apples $A^2$: photometric redshift predictions for next-generation surveys
Ascaso, Mei, Benitez
Compare the expected performance of two of the largest stage IV next-generation surveys in the optical and IR (LSST and Euclid), with a particular focus on cluster surveys. In this first paper, introduce the mock catalogues: an N-body sim+semi-analytical cone with a posterior modification with PhotReal, a technique which modifies the original photometry to make it more realistic by using an empirical library of spectral templates. Confirmed the reliability of the mock catalogue by comparing the obtained color-magnitude relation, the luminosity and MF and the angular correlation function with those of real data. Also analyze the behavior of the expected photo-z for each survey, in terms of photometric resolution, photometric z bias and fraction of outliers. In addition, discuss the benefits of using the BPZ odds photo-z quality parameter to select the best quality data of the sample. Find that very deep NIR surveys such as Euclid will provide very good performance (Delta z / (1+z)~0.025-0.053) down to H~24 AB mag and up to z~3 depending on the optical observations available from the ground whereas extremely deep optical surveys such as LSST will obtain an overall lower photo-z resolution (0.045) down to i~27.5 AB mag, being substantially improved (0.035) if restricting the sample down to i~24 AB mag. Highlight the fact that those numbers can be improved substantially by selecting a subsample of galaxies with the best quality photo-z. Finally discuss the impact that these surveys will have for the community in terms of photos legacy once the data is available.
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