[5] arXiv:0808.0194 [ps, pdf, other] Title: Mergers and Mass Accretion Rates in Galaxy Assembly: The Millennium Simulation Compared to Observations of z~2 Galaxies Authors: S. Genel, R. Genzel, N. Bouché, A. Sternberg, T. Naab, N. M. Förster Schreiber, K. L. Shapiro, L. J. Tacconi, D. Lutz, G. Cresci, P. Buschkamp, R. I. Davies, E. K. S. Hicks Comments: 5 pages, 4 figures, Accepted for publication in ApJ Subjects: Astrophysics (astro-ph) Recent observations of UV-/optically selected, massive star forming galaxies at z~2 indicate that the baryonic mass assembly and star formation history is dominated by continuous rapid accretion of gas and internal secular evolution, rather than by major mergers. We use the Millennium Simulation to build new halo merger trees, and extract halo merger fractions and mass accretion rates. We find that even for halos not undergoing major mergers the mass accretion rates are plausibly sufficient to account for the high star formation rates observed in z~2 disks. On the other hand, the fraction of major mergers in the Millennium Simulation is sufficient to account for the number counts of submillimeter galaxies (SMGs), in support of observational evidence that these are major mergers. When following the fate of these two populations in the Millennium Simulation to z=0, we find that subsequent mergers are not frequent enough to convert all z~2 turbulent disks into elliptical galaxies at z=0. Similarly, mergers cannot transform the compact SMGs/red sequence galaxies at z~2 into observed massive cluster ellipticals at z=0. We argue therefore, that secular and internal evolution must play an important role in the evolution of a significant fraction of z~2 UV-/optically and submillimeter selected galaxy populations. arXiv:0808.0494 [ps, pdf, other] Title: Simulations of AGN feedback in galaxy clusters and groups: impact on gas fractions and the Lx-T scaling relation Authors: Ewald Puchwein, Debora Sijacki, Volker Springel Comments: 5 pages, 2 figures, submitted to ApJL Subjects: Astrophysics (astro-ph) Recently, rapid observational and theoretical progress has established that black holes (BHs) play a decisive role in the formation and evolution of individual galaxies as well as galaxy groups and clusters. In particular, there is compelling evidence that BHs vigorously interact with their surroundings in the central regions of galaxy clusters, indicating that any realistic model of galaxy cluster formation needs to account for these astrophysical processes. This is also suggested by the failure of previous generations of hydrodynamical simulations without BH physics to simultaneously account for the paucity of strong cooling flows in clusters, the slope and amplitude of the observed cluster scaling relations, and the high-luminosity cut-off of central cluster galaxies. Here we use high-resolution cosmological simulations of a large sample of galaxy clusters and groups to study how BHs affect their host systems. We focus on two specific properties, the halo gas fraction and the X-ray luminosity temperature scaling relation, both of which are notoriously difficult to reproduce in self-consistent hydrodynamical simulations. We show that BH feedback can provide a solution to both of these issues, bringing them in excellent agreement with observations, without alluding to the `cooling only' solution that produces unphysically bright central galaxies. By comparing a large sample of simulated AGN-heated clusters with observations, our new simulation technique should make it possible to reliably calibrate observational biases in cluster surveys, thereby enabling various high-precision cosmological studies of the dark matter and dark energy content of the universe. arXiv:0808.0524 [ps, pdf, other] Title: Population III Supernovae and the Assembly of the First Galaxies Authors: Daniel Whalen, Bob Van Veelen, Brian W. O'Shea, Michael L. Norman Comments: 5 pages, 4 figures, to appear in the IAUS 255 conference proceedings Low-Metallicity Star Formation: from the First Stars to Dwarf Galaxies, L.K. Hunt, S. Madden and R. Schneider eds Subjects: Astrophysics (astro-ph) Current numerical studies suggest that the first galaxies formed a few stars at a time and were enriched only gradually by the first heavy elements. However, the large box sizes in these models cannot resolve primordial supernova explosions or the mixing of their metals with ambient gas, which could result in intervening, prompt generations of low-mass stars. We present multiscale 1D models of Population III supernovae in cosmological halos that evolve the blast from its earliest stages as a free expansion. We find that if the star ionizes the halo, the ejecta strongly interacts with the dense shell swept up by the H II region, potentially cooling and fragmenting it into clumps that are unstable to gravitational collapse. If the star fails to ionize the halo, the explosion propagates metals out to 20 - 40 pc and then collapses, enriching tens of thousands of solar masses of primordial gas, in contrast to previous models that suggest such explosions 'fizzle'. Rapid formation of low-mass stars trapped in the gravitational potential well of the halo appears to be inevitable in such circumstances. Consequently, it is possible that far more stars were swept up into the first galaxies, at earlier times and with distinct chemical signatures, than in present models. Upcoming measurements by JWST and ALMA may discriminate between these two paradigms. arXiv:0808.0539 [ps, pdf, other] Title: Galaxy Groups in the SDSS DR4: III. the luminosity and stellar mass functions Authors: Xiaohu Yang (SHAO), H.J. Mo (UMass), Frank C. van den Bosch (MPIA) Comments: 17 pages, 7 figures. Submitted for publication in ApJ Subjects: Astrophysics (astro-ph) Using a large galaxy group catalogue constructed from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) with an adaptive halo-based group finder, we investigate the luminosity and stellar mass functions for different populations of galaxies (central versus satellite; red versus blue; and galaxies in groups of different masses) and for groups themselves. The conditional stellar mass function (CSMF), which describes the stellar distribution of galaxies in halos of a given mass for central and satellite galaxies can be well modeled with a log-normal distribution and a modified Schechter form, respectively. On average, there are about 3 times as many central galaxies as satellites. Among the satellite population, there are in general more red galaxies than blue ones. For the central population, the luminosity function is dominated by red galaxies at the massive end, and by blue galaxies at the low mass end. At the very low-mass end ($M_\ast \la 10^9 h^{-2}\Msun$), however, there is a marked increase in the number of red centrals. We speculate that these galaxies are located close to large halos so that their star formation is truncated by the large-scale environments. The stellar-mass function of galaxy groups is well described by a double power law, with a characteristic stellar mass at $\sim 4\times 10^{10}h^{-2}\Msun$. Finally, we use the observed stellar mass function of central galaxies to constrain the stellar mass - halo mass relation for low mass halos, and obtain $M_{\ast, c}\propto M_h^{4.9}$ for $M_h \ll 10^{11} \msunh$. arXiv:0808.0553 [ps, pdf, other] Title: Early Massive Galaxy Formation by Cold Streams Through Hot Haloes Authors: A. Dekel, Y. Birnboim, G. Engel, J. Freundlich, T. Goerdt, M. Mumcuoglu, E. Neistein, C. Pichon, R. Teyssier, E. Zinger Comments: 23 pages, 13 figures, Letter submitted to Nature with Supplementary Information Subjects: Astrophysics (astro-ph) The massive galaxies in the young universe, ten billion years ago, formed stars at surprising intensities. While this was commonly attributed to violent mergers, many of these galaxies seem to be extended rotating discs incompatible with mergers (Genzel et al. 2006, 2008). In order to uncover the origin of this phenomenon, we use a state-of-the-art cosmological simulation and clustering theory to explore how these galaxies acquired their gas. We find that these are "Stream-Fed Galaxies", growing via steady, narrow, cold gas streams, which penetrate effectively through the shock-heated media of dark-matter haloes as massive as the Milky Way's. This confirms an earlier conjecture (Dekel & Birnboim 2006). Half the stream mass is in clumps leading to mergers of mass ratio 1:10 or higher, and half is in smoother flows. Since the merger duty cycle is 0.1, three-quarters of the galaxies forming stars at a given rate are fed by smooth streams. Unlike destructive major mergers, the smoother flows can keep the discs intact, though thick and perturbed. The observed abundance of star-forming galaxies implies that the inflowing gas turns into stars at maximum efficiency. In contrast, the sub-millimeter galaxies that form stars even more intensely are largely compact merger-induced starbursts in haloes twice as massive. arXiv:0808.0716 [ps, pdf, other] Title: Bulge Formation by the Coalescence of Giant Clumps in Primordial Disk Galaxies Authors: Bruce G. Elmegreen (1), Frederic Bournaud (2), Debra Meloy Elmegreen (3) ((1) IBM Watson Research Center, (2) Laboratoire AIM, CEA-Saclay, (3) Vassar College) Comments: 21 pages, 9 figures, ApJ 688, November 20 2008, in press Subjects: Astrophysics (astro-ph) Gas-rich disks in the early universe are highly turbulent and have giant star-forming clumps. Models suggest the clumps form by gravitational instabilities, and if they resist disruption by star formation, then they interact, lose angular momentum, and migrate to the center to form a bulge. Here we study the properties of the bulges formed by this mechanism. They are all thick, slowly rotating, and have a high Sersic index, like classical bulges. Their rapid formation should also give them relatively high alpha-element abundances. We consider fourteen low-resolution models and four high-resolution models, three of which have supernova feedback. All models have an active halo, stellar disk, and gaseous disk, three of the models have a pre-existing bulge and three others have a cuspy dark matter halo. All show the same basic result except the one with the highest feedback, in which the clumps are quickly destroyed and the disk thickens too much. The coalescence of massive disk clumps in the center of a galaxy is like a major merger in terms of orbital mixing. It differs by leaving a bulge with no specific dark matter component, unlike the merger of individual galaxies. Normal supernova feedback has little effect because the high turbulent speed in the gas produces tightly bound clumps. A variety of indirect observations support the model, including clumpy disks with young bulges at high redshift and bulges with relatively little dark matter. arXiv:0808.0721 [ps, pdf, other] Title: SDSS J120923.7+264047: A new massive galaxy cluster with a bright giant arc Authors: Eran O. Ofek, Stella Seitz, Felix Klein Comments: MNRAS, in press Subjects: Astrophysics (astro-ph) Highly magnified lensed galaxies allow us to probe the morphological and spectroscopic properties of high-redshift stellar systems in great detail. However, such objects are rare, and there are only a handful of lensed galaxies which are bright enough for a high-resolution spectroscopic study with current instrumentation. We report the discovery of a new massive lensing cluster, SDSS J120923.7+264047, at z=0.558. Present around the cluster core, at angular distances of up to ~40'', are many arcs and arc candidates, presumably due to lensing of background galaxies by the cluster gravitational potential. One of the arcs, 21'' long, has an r-band magnitude of 20, making it one of the brightest known lensed galaxies. We obtained a low-resolution spectrum of this galaxy, using the Keck-I telescope, and found it is at redshift of z=1.018. arXiv:0808.0911 [ps, pdf, other] Title: A Confirmation of the Strong Clustering of Distant Red Galaxies at 2 < z <3 Authors: Ryan F. Quadri, Rik J. Williams, Kyoung-Soo Lee, Marijn Franx, Pieter van Dokkum, Gabriel B. Brammer Comments: Accepted for publication in ApJ Letters Subjects: Astrophysics (astro-ph) Recent studies have shown that distant red galaxies (DRGs), which dominate the high-mass end of the galaxy population at z~2.5, are more strongly clustered than the population of blue star-forming galaxies at similar redshifts. However these studies have been severely hampered by the small sizes of fields having deep near-infrared imaging. Here we use the large UKIDSS Ultra Deep Survey to study the clustering of DRGs. The size and depth of this survey allows for an unprecedented measurement of the angular clustering of DRGs at 2 = 321 km s^-1), low surface brightness ( = 20.8 mag arcsec^-2), and large effective radii ( = 11.4 kpc), and have = 1.5 x 10^12 M_sun and = 12.4. In contrast, properties of the RQ hosts are = 241 km s^-1, ~ 4.4 x 10^11 M_sun, and ~ 5.3. The distinction between these galaxies occurs at sigma_* ~ 300 km s^-1, R_e ~ 6 kpc, and corresponding M_* ~ 5.9 +/- 3.5 x 10^11 M_sun. Our data support previous results that PG QSOs are related to gas-rich galaxy mergers that form intermediate-mass galaxies, while RL QSOs reside in massive early-type galaxies, most of which also show signs of recent mergers or interactions. Most previous work has drawn these conclusions by using estimates of the black hole mass and inferring host galaxy properties from that, while here we have relied purely on directly measured host galaxy properties.