[1] arXiv:0810.1734 [ps, pdf, other] Title: Central mass and luminosity of Milky Way satellites in the LCDM model Authors: Andrea V. Maccio' (MPIA), Xi Kang (MPIA), Ben Moore (Univ. Zurich) Comments: 4 pages, 3 figures, submitted to ApJ Letters Subjects: Astrophysics (astro-ph) It has been recently pointed out that Milky Way satellites all have a common mass around 1.0e7 Msun within 300 pc (M_{0.3}), while they span almost four orders of magnitude in luminosity. It is argued that this may reflect a specific scales for galaxy formation or a scale for dark matter clustering. Here we use numerical simulations coupled with a semi-analytic model for galaxy formation, to predict the central mass and luminosity of galactic satellites in the LCDM model. We show that this common mass scale can be easily explained within the Cold Dark Matter scenario when the physics of galaxy formation is taken into account. The narrow range of M_{0.3} comes from the narrow distribution of circular velocities at time of accretion (peaking around 20 km/s) for satellites able to form stars. The wide range of satellite luminosities is due to the broad distribution of accretion redshift for a given circular velocity. This causes the satellite baryonic content to be suppressed by photo-ionization to different extent. Our results favor the argument that the common mass M_{0.3} reflects a specific scale (circular velocity ~20 km/s or M~1.e9 Msun) for star formation. [5] arXiv:0810.1748 [ps, pdf, other] Title: Rescuing the Initial Mass Function for Arp 78 Authors: Ralf Kotulla, Uta Fritze, John S Gallagher III Comments: accepted for publication in ApJ Letters; 4 pages, 2 figures; uses emulateapj Subjects: Astrophysics (astro-ph) We present deep R and narrow-band Halpha images of Arp 78 obtained with the WIYN 3.5-m telescope on Kitt Peak. GALEX observations had shown a very extended UV structure for this system, reaching beyond the optical radius of Arp 78 and also beyond its previously known Halpha-radius. Our new Halpha data now show agreement not only with the spatial extent of the near- and far-UV maps, but also in terms of structural details. Star formation rates derived from L(Halpha) and L(FUV) are in reasonable agreement, indicating that in this case the upper stellar IMF in the UV-bright outer arm is relatively normal. The star forming sites in the outer arms are younger than ~15 Myr and massive enough to properly sample the IMF up to high masses; their low optical visibility evidently is a property of their youth. [40] arXiv:0810.1917 [pdf, other] Title: Evolution of the Color-Magnitude Relation in Galaxy Clusters at z ~1 from the ACS Intermediate Redshift Cluster Survey Authors: Simona Mei, Brad P. Holden, John P. Blakeslee, Holland C. Ford, Marijn Franx, Nicole L. Homeier, Garth D. Illingworth, Myungkook J. Jee, Roderik Overzier, Marc Postman, Piero Rosati, Arjen van der Wel, James G. Bartlett Comments: ApJ, in press, 27 pages, 22 figures Subjects: Astrophysics (astro-ph) We apply detailed observations of the Color-Magnitude Relation (CMR) with the ACS/HST to study galaxy evolution in eight clusters at z~1. The early-type red sequence is well defined and elliptical and lenticular galaxies lie on similar CMRs. We analyze CMR parameters as a function of redshift, galaxy properties and cluster mass. For bright galaxies (M_B < -21mag), the CMR scatter of the elliptical population in cluster cores is smaller than that of the S0 population, although the two become similar at faint magnitudes. While the bright S0 population consistently shows larger scatter than the ellipticals, the scatter of the latter increases in the peripheral cluster regions. If we interpret these results as due to age differences, bright elliptical galaxies in cluster cores are on average older than S0 galaxies and peripheral elliptical galaxies (by about 0.5Gyr). CMR zero point, slope, and scatter in the (U-B)_z=0 rest-frame show no significant evolution out to redshift z~1.3 nor significant dependence on cluster mass. Two of our clusters display CMR zero points that are redder (by ~2sigma) than the average (U-B)_z=0 of our sample. We also analyze the fraction of morphological early-type and late-type galaxies on the red sequence. We find that, while in the majority of the clusters most (80% to 90%) of the CMR population is composed of early-type galaxies, in the highest redshift, low mass cluster of our sample, the CMR late-type/early-type fractions are similar (~50%), with most of the late-type population composed of galaxies classified as S0/a. This trend is not correlated with the cluster's X-ray luminosity, nor with its velocity dispersion, and could be a real evolution with redshift. [2] arXiv:0810.1953 [ps, pdf, other] Title: Structural Properties of Pseudo-Bulges, Classical Bulges and Elliptical Galaxies: an SDSS Perspective Authors: Dimitri A. Gadotti (Max Planck Institute for Astrophysics) Comments: 23 pages, 20 figures, 4 tables; MNRAS submitted, comments welcome; high resolution version available as PDF file at this http URL Subjects: Astrophysics (astro-ph) We have performed 2D bulge/bar/disc decompositions using g, r and i-band images of a representative sample of nearly 1000 galaxies from the Sloan Digital Sky Survey. We show that the Petrosian concentration index is a better proxy for bulge-to-total ratio than the global Sersic index. We show that pseudo-bulges can be distinguished from classical bulges as outliers in the Kormendy relation. We provide the structural parameters and distributions of stellar masses of ellipticals, classical bulges, pseudo-bulges, discs and bars, and find that 32 per cent of the total stellar mass in massive galaxies in the local universe is contained in ellipticals, 36 per cent in discs, 25 per cent in classical bulges, 3 per cent in pseudo-bulges and 4 per cent in bars. Pseudo-bulges are currently undergoing intense star formation activity and populate the blue cloud of the colour-magnitude diagram. Most (though not all) classical bulges are quiescent and populate the red sequence of the diagram. Classical bulges follow a correlation between bulge Sersic index and bulge-to-total ratio, while pseudo-bulges do not. In addition, for a fixed bulge-to-total ratio, pseudo-bulges are less concentrated than classical bulges. Pseudo-bulges follow a mass-size relation similar to that followed by bars, and different from that followed by classical bulges. In the fundamental plane, pseudo-bulges occupy the same locus as discs. While these results point out different formation processes for classical and pseudo-bulges, we also find a significant overlap in their properties, indicating that the different processes might happen concomitantly. Finally, classical bulges and ellipticals follow offset mass-size relations, suggesting that high-mass bulges might not be simply high-mass ellipticals surrounded by discs. [50] arXiv:0810.2245 [ps, pdf, other] Title: The zCOSMOS redshift survey: the three-dimensional classification cube and bimodality in galaxy physical properties Authors: M. Mignoli, G. Zamorani, M. Scodeggio, A. Cimatti, C. Halliday, S.J. Lilly, L. Pozzetti, D. Vergani, C.M. Carollo, T. Contini, O. Le Fevre, V. Mainieri, A. Renzini, S. Bardelli, M. Bolzonella, A. Bongiorno, K. Caputi, G. Coppa, O. Cucciati, S. de la Torre, L. de Ravel, P. Franzetti, B. Garilli, A. Iovino, P. Kampczyk, J.-P. Kneib, C. Knobel, K. Kovac, F. Lamareille, J.-F. Le Borgne, V. Le Brun, C. Maier, R. Pello, Y. Peng, E. Perez Montero, E. Ricciardelli, C. Scarlata, J.D. Silverman, M. Tanaka, L. Tasca, L. Tresse, E. Zucca, U. Abbas, D. Bottini, P. Capak, A. Cappi, P. Cassata, M. Fumana, L. Guzzo, A. Leauthaud, D. Maccagni, C. Marinoni, H.J. McCracken, P. Memeo, B. Meneux, P. Oesch, C. Porciani, R. Scaramella, N. Scoville Comments: 11 pages, Accepted for publication in A&A Subjects: Astrophysics (astro-ph) Aims. We investigate the relationships between three main optical galaxy observables (spectral properties, colours, and morphology), exploiting the data set provided by the COSMOS/zCOSMOS survey. The purpose of this paper is to define a simple galaxy classification cube, using a carefully selected sample of around 1000 galaxies. Methods. Using medium resolution spectra of the first 1k zCOSMOS-bright sample, optical photometry from the Subaru/COSMOS observations, and morphological measurements derived from ACS imaging, we analyze the properties of the galaxy population out to z~1. Applying three straightforward classification schemes (spectral, photometric, and morphological), we identify two main galaxy types, which appear to be linked to the bimodality of galaxy population. The three parametric classifications constitute the axes of a "classification cube". Results. A very good agreement exists between the classification from spectral data (quiescent/star-forming galaxies) and that based on colours (red/blue galaxies). The third parameter (morphology) is less well correlated with the first two: in fact a good correlation between the spectral classification and that based on morphological analysis (early-/late-type galaxies) is achieved only after partially complementing the morphological classification with additional colour information. Finally, analyzing the 3D-distribution of all galaxies in the sample, we find that about 85% of the galaxies show a fully concordant classification, being either quiescent, red, bulge-dominated galaxies (~20%) or star-forming, blue, disk-dominated galaxies (~65%). These results imply that the galaxy bimodality is a consistent behaviour both in morphology, colour and dominant stellar population, at least out to z~1. 51] arXiv:0810.2248 [ps, pdf, other] Title: MCAO near-IR photometry of the Globular Cluster NGC 6388: MAD observations in crowded fields Authors: A. Moretti (INAF/OaPD), G. Piotto (Univ. Padova), C. Arcidiacono (INAF/OaPD), A. P. Milone (Univ. Padova), R. Ragazzoni (INAF/OaPD), R. Falomo (INAF/OaPD), J. Farinato (INAF/OaPD), L. R. Bedin (STScI), J. Anderson (STScI), A. Sarajedini (Univ. Florida), A. Baruffolo (INAF/OaPD), E. Diolaiti (INAF/OaBO), M. Lombini (INAF/OaBO), R. Brast (ESO), R. Donaldson (ESO), J. Kolb (ESO), E. Marchetti (ESO), S. Tordo (ESO) Comments: 9 pages, 10 figures. Accepted for publication on A. & A Subjects: Astrophysics (astro-ph) Deep photometry of crowded fields, such as Galactic Globular Clusters, is severely limited by the actual resolution of ground-based telescopes. On the other hand, the Hubble Space Telescope does not provide the near-infrared (NIR) filters needed to allow large color baselines. In this work we aim at demonstrating how ground based observations can reach the required resolution when using Multi-Conjugated Adaptive Optic (MCAO) devices in the NIR, such as the experimental infrared camera (MAD) available on the VLT. This is particularly important since these corrections are planned to be available on all ground--based telescopes in the near future. We do this by combining the infrared photometry obtained by MAD/VLT with ACS/HST optical photometry of our scientific target, the bulge globular cluster NGC 6388, in which we imaged two fields. In particular, we constructed color-magnitude diagrams with an extremely wide color baseline in order to investigate the presence of multiple stellar populations in this cluster. From the analysis of the external field, observed with better seeing conditions, we derived the deepest optical-NIR CMD of NGC 6388 to date. The high-precision photometry reveals that two distinct sub-giant branches are clearly present in this cluster. We also use the CMD from the central region to estimate the distance ((m-M)=15.33) and the reddening (E(B-V)=0.38) for this cluster. We estimate the age to be ~11.5+/- 1.5 Gyr. The large relative-age error reflects the bimodal distribution of the SGB stars. This study clearly demonstrates how MCAO correction in the NIR bands implemented on ground based telescopes can complement the high-resolution optical data from HST. [7] arXiv:0810.2304 [ps, pdf, other] Title: Are the kinematics of DLAs in agreement with their arising in the gas disks of galaxies? Authors: Martin Zwaan (1), Fabian Walter (2), Emma Ryan-Weber (3), Elias Brinks (4), W.J.G. de Blok (5), Robert C. Kennicutt Jr. (3) ((1) ESO Garching, (2) MPIA Heidelberg, (3) IoA Cambridge, (4) U. Hertfordshire, (5) U. Cape Town) Comments: Accepted for publication in the AJ special THINGS issue. For a high-resolution version visit: this http URL Subjects: Astrophysics (astro-ph) We demonstrate in this paper that the velocity widths of the neutral gas in Damped Ly Alpha (DLA) systems are inconsistent with these systems originating in gas disks of galaxies similar to those seen in the local Universe. We examine the gas kinematics of local galaxies using the high quality HI 21-cm data from the HI Nearby Galaxies Survey (THINGS) and make a comparison with the velocity profiles measured in the low-ionization metal lines observed in DLAs at high redshifts. The median velocity width of z=0 HI gas above the DLA column density limit of N=2x10^20 cm-2 is approximately 30 km/s, whereas the typical value in DLAs is a factor of two higher. We argue that the gas kinematics at higher redshifts are increasingly influenced by gas that is not participating in ordered rotation in cold disks, but is more likely associated with tidal gas related to galaxy interactions or processes such as superwinds and outflows. An analysis of the HI in the local interacting star-burst galaxy M82 shows that the velocity widths in this galaxy are indeed similar to what is seen in DLAs. [9] arXiv:0810.2314 [pdf, other] Title: GRB 080913 at redshift 6.7 Authors: J. Greiner, T. Kruehler, J.P.U. Fynbo, A. Rossi, R. Schwarz, S. Klose, S. Savaglio, N.R. Tanvir, S. McBreen, T. Totani, B.B. Zhang, X.F. Wu, D. Watson, S.D. Barthelmy, A.P. Beardmore, P. Ferrero, N. Gehrels, D.A. Kann, N. Kawai, A. Kuepcue Yoldas, P. Meszaros, B. Milvang-Jensen, S.R. Oates, D. Pierini, P. Schady, K. Toma, P.M. Vreeswijk, A. Yoldas, B. Zhang, P. Afonso, K. Aoki, D.N. Burrows, C. Clemens, R. Filgas, Z. Haiman, D.H. Hartmann, G. Hasinger, J. Hjorth, E. Jehin, A.J. Levan, E.W. Liang, D. Malesani, T.-S. Pyo, S. Schulze, G. Szokoly, H. Terada, K. Wiersema Comments: 14 pages, 7 figures, ApJ (subm) Subjects: Astrophysics (astro-ph) We report on the detection by Swift of GRB 080913, and subsequent optical/near-infrared follow-up observations by GROND which led to the discovery of its optical/NIR afterglow and the recognition of its high-z nature via the detection of a spectral break between the i' and z' bands. Spectroscopy obtained at the ESO-VLT revealed a continuum extending down to lambda = 9400 A, and zero flux for 7500 A < lambda<9400 A, which we interpret as the onset of a Gunn-Peterson trough at z=6.695+-0.025 (95.5% conf. level), making GRB 080913 the highest redshift GRB to date, and more distant than the highest-redshift QSO. We note that many redshift indicators which are based on promptly available burst or afterglow properties have failed for GRB 080913. We report on our follow-up campaign and compare the properties of GRB 080913 with bursts at lower redshift. In particular, since the afterglow of this burst is fainter than typical for GRBs, we show that 2m-class telescopes can identify most high-redshift GRBs. arXiv:0810.2391 [ps, pdf, other] Title: Geometrically Derived Timescales for Star Formation in Spiral Galaxies Authors: D. Tamburro, H.-W. Rix, F. Walter, E. Brinks, W.J.G. de Blok, R.C. Kennicutt, M.-M. Mac Low Comments: Accepted for publication in the AJ special THINGS issue. For a high-resolution version visit: this http URL Subjects: Astrophysics (astro-ph) We estimate a characteristic timescale for star formation in the spiral arms of disk galaxies, going from atomic hydrogen (HI) to dust-enshrouded massive stars. Drawing on high-resolution HI data from The HI Nearby Galaxy Survey and 24$\mu$m images from the Spitzer Infrared Nearby Galaxies Survey we measure the average angular offset between the HI and 24$\mu$m emissivity peaks as a function of radius, for a sample of 14 nearby disk galaxies. We model these offsets assuming an instantaneous kinematic pattern speed, $\Omega_p$, and a timescale, t(HI-->24$\mu$m), for the characteristic time span between the dense \hi phase and the formation of massive stars that heat the surrounding dust. Fitting for $\Omega_p$ and t(HI-->24$\mu$m), we find that the radial dependence of the observed angular offset (of the \hi and 24$\mu$m emission) is consistent with this simple prescription; the resulting corotation radii of the spiral patterns are typically $R_{cor}\simeq 2.7 R_{s}$, consistent with independent estimates. The resulting values of t(HI-->24$\mu$m) for the sample are in the range 1--4 Myr. We have explored the possible impact of non-circular gas motions on the estimate of t(HI-->24$\mu$m) and have found it to be substantially less than a factor of 2. This implies that a short timescale for the most intense phase of the ensuing star formation in spiral arms, and implies a considerable fraction of molecular clouds exist only for a few Myr before forming stars. However, our analysis does not preclude that some molecular clouds persist considerably longer. If much of the star formation in spiral arms occurs within this short interval t(HI-->24$\mu$m), then star formation must be inefficient, in order to avoid the short-term depletion of the gas reservoir. [34] arXiv:0810.2518 [ps, pdf, other] Title: Obscured and powerful AGN and starburst activities at z~3.5 Authors: M. Polletta, A. Omont, S. Berta, J. Bergeron, C. S. Stalin, P. Petitjean, M. Giorgetti, G. Trinchieri, R. Srianand, H. J. McCracken, Y. Pei, H. Dannerbauer Comments: Accepted for publication in Astronomy & Astrophysics (12 pages; 6 figures) Subjects: Astrophysics (astro-ph) We report the discovery of two sources at z=3.867 and z=3.427 that exhibit powerful starburst and AGN activities. They benefit from data from radio to X rays from the CFHTLS-D1/SWIRE/XMDS surveys. Follow-up optical and near-infrared spectroscopy, and millimeter IRAM/MAMBO observations are also available. We performed an analysis of their spectral energy distributions to understand the origin of their emission and constrain their luminosities. A comparison with other composite systems at similar redshifts from the literature is also presented. The AGN and starburst bolometric luminosities are ~10^13 Lsun. The AGN emission dominates at X ray, optical, mid-infrared wavelengths, and probably in the radio. The starburst emission dominates in the far-infrared. The estimated star formation rates range from 500 to 3000Msun/yr. The AGN near-infrared and X ray emissions are heavily obscured in both sources with an estimated dust extinction Av>4, and Compton-thick gas column densities. The two sources are the most obscured and most luminous AGNs detected at millimeter wavelengths currently known. The sources presented in this work are heavily obscured QSOs, but their properties are not fully explained by the standard AGN unification model. In one source, the ultraviolet and optical spectra suggest the presence of outflowing gas and shocks, and both sources show emission from hot dust, most likely in the vicinity of the nucleus. Evidence of moderate AGN-driven radio activity is found in both sources. The two sources lie on the local M_BH-M_bulge relation. To remain on this relation, their star formation rate has to decrease. Our results support evolutionary models that invoke radio feedback as star formation quenching mechanism, and suggest that such a mechanism might play a major role also in powerful AGNs. [2] arXiv:0810.2534 [ps, pdf, other] Title: Secular Evolution in Disk Galaxies: Pseudobulge Growth and the Formation of Spheroidal Galaxies Authors: John Kormendy, David B. Fisher Comments: 11 pages, 6 Postscript figures; requires asp2006.sty; as published, except with updated references; for a version with full resolution figures, see this http URL Journal-ref: Kormendy, J., & Fisher, D. B. 2008, in Formation and Evolution of Galaxy Disks, ed. J. G. Funes, S. J. & E. M. Corsini (San Francisco: ASP), 297 Subjects: Astrophysics (astro-ph) Updating Kormendy & Kennicutt (2004, ARAA, 42, 603), we review internal secular evolution of galaxy disks. One consequence is the growth of pseudobulges that often are mistaken for true (merger-built) bulges. Many pseudobulges are recognizable as cold, rapidly rotating, disky structures. Bulges have Sersic function brightness profiles with index n > 2; most pseudobulges have n <= 2. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many pure disk galaxies with no evidence for merger-built bulges? E. g., the giant Scd galaxies M101 and NGC 6946 have rotation velocities of V ~ 200 km/s but nuclear star clusters with velocity dispersions of 25 to 40 km/s. Within 8 Mpc of us, 11 of 19 galaxies with V > 150 km/s show no evidence for a classical bulge, while only 7 are ellipticals or have classical bulges. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories. Our second theme is environmental secular evolution. We confirm that spheroidal galaxies have fundamental plane (FP) correlations that are almost perpendicular to those for bulges and ellipticals. Spheroidals are not dwarf ellipticals. Rather, their structural parameters are similar to those of late-type galaxies. We suggest that spheroidals are defunct late-type galaxies transformed by internal processes such as supernova-driven gas ejection and environmental processes such as secular harassment and ram-pressure stripping. Minus spheroidals, the FP of ellipticals and bulges has small scatter. With respect to these, pseudobulges are larger and less dense. [4] arXiv:0810.2537 [ps, pdf, other] Title: Simulating Subhalos at High Redshift: Galaxy Merger Rates, Counts, and Types Authors: Andrew R. Wetzel, J.D. Cohn, Martin White Comments: 17 pages, 12 figures, submitted to MNRAS Subjects: Astrophysics (astro-ph) We use high-resolution N-body simulations of cosmological volumes to calculate the statistical properties of subhalo (galaxy) major mergers at high redshift (z=0.6-5). We measure the evolution of the galaxy merger rate, finding that it is much shallower than the merger rate of dark matter host halos at z>2.5, but roughly parallels that of halos at z<1.6. We also track the detailed merger histories of individual galaxies and measure the likelihood of multiple mergers per halo or subhalo. We examine satellite merger statistics in detail: 15%-35% of all recently merged galaxies are satellites and satellites are twice as likely as centrals to have had a recent major merger. Finally, we show how the differing evolution of the merger rates of halos and galaxies leads to the evolution of the average satellite occupation per halo, noting that for a fixed halo mass, the satellite halo occupation peaks at z~2.5. [4] arXiv:0810.2788 [ps, pdf, other] Title: A Steep Faint-End Slope of the UV Luminosity Function at z~2-3: Implications for the Global Stellar Mass Density and Star Formation in Low Mass Halos Authors: Naveen A. Reddy (NOAO), Charles C. Steidel (Caltech) Comments: 29 pages, 15 figures, 7 tables; accepted for publication in ApJ Subjects: Astrophysics (astro-ph) We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (alpha) of the UV LF at redshifts 1.92000 spectroscopic redshifts and ~31000 LBGs in 31 spatially-independent fields over a total area of 3261 arcmin^2. These data allow us to select galaxies to 0.07L* and 0.10L* at z~2 and z~3, respectively. A maximum likelihood analysis indicates steep values of alpha(z=2)=-1.73+/-0.07 and alpha(z=3)=-1.73+/-0.13. This result is robust to luminosity dependent systematics in the Ly-alpha equivalent width and reddening distributions, is similar to the steep values advocated at z>4, and implies that ~93% of the unobscured UV luminosity density at z~2-3 arises from sub-L* galaxies. With a realistic luminosity dependent reddening distribution, faint to moderately luminous galaxies account for >70% and >25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.92 contrasts with the shallower value inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of low mass halos capable of supporting star formation at z<2. [Abridged] [7] arXiv:0810.2794 [ps, pdf, other] Title: The Correlation of Star Formation Quenching with Internal Galaxy Properties and Environment Authors: Taysun Kimm, Rachel S. Somerville, Sukyoung K. Yi, Frank C. van den Bosch, Samir Salim, Fabio Fontanot, Pierluigi Monaco, Houjun Mo, Anna Pasquali, R. M. Rich, Xiaohu Yang Comments: 18 pages, 11 figures, submitted to MNRAS Subjects: Astrophysics (astro-ph) We investigate the correlation of star formation quenching with internal galaxy properties and large scale environment (halo mass) in empirical data and theoretical models. We make use of the halo-based Group Catalog of Yang and collaborators, which is based on the Sloan Digital Sky Survey. Data from the Galaxy Evolution Explorer (GALEX) are also used to extract the recent star formation rate. In order to investigate the environmental effects, we examine the properties of ``central'' and ``satellite'' galaxies separately. For central galaxies, we find that the fractions of ``red'' and ``passive'' galaxies in the observational group catalogs are a strong function of halo mass at fixed stellar mass, and a weak function of stellar mass at fixed halo mass. For satellite galaxies, a nearly equally strong dependence on halo mass and stellar mass is seen. We make the same comparison for five different semi-analytic models based on three independently developed codes. We find that the models with AGN feedback reproduce reasonably well the dependence of the fraction of central red and passive galaxies on halo mass and stellar mass. However, for satellite galaxies, the same models badly overproduce the fraction of red/passive galaxies and do not reproduce the empirical trends with stellar mass or halo mass. This {\em satellite overquenching problem} is caused by the too-rapid stripping of the satellites' hot gas halos, which leads to rapid strangulation of star formation.