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Kimm, Taysun,Cen, Renyue,Rosdahl, Joakim,Yi, Sukyoung K. American Astronomical Society 2016 The Astrophysical journal Vol.823 No.1
<P>We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with M-halo similar to 4 X 10(7) M-circle dot at z > 10 using cosmological radiation-hydrodynamics simulations. We find that very compact (less than or similar to 1 pc) and massive (similar to 6 X 10(5) M-circle dot.)clusters form rapidly when pristine gas collapses isothermally with the aid of efficient Ly alpha emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short (<< 1 Myr), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. The simulated clusters closely resemble the local GCs in mass and size but show a metallicity spread that is much wider than found in the local GCs. We discuss a role of pre-enrichment by Pop III and II stars as a potential solution to the latter issue. Although not without shortcomings, it is encouraging that a naive blind (not tuned) cosmological simulation presents a possible channel for the formation of at least some massive GCs.</P>
THE IMPACT OF GAS STRIPPING AND STELLAR MASS LOSS ON SATELLITE GALAXY EVOLUTION
Kimm, Taysun,Yi, Sukyoung K.,Khochfar, Sadegh IOP Publishing 2011 The Astrophysical journal Vol.729 No.1
<P>Current semi-analytic models of galaxy formation overpredict the fraction of passive small late-type satellite galaxies in dense environments by a factor of two to three. We hypothesize that this is due to inaccurate prescriptions on cold gas evolution. In the hope of solving this problem, we apply detailed prescriptions on the evolution of diffuse hot gases in satellites and on stellar mass loss, both of which are critical in modeling cold gas evolution. We replace the conventional shock-heating motivated instant stripping with a realistic gradual prescription based on ram pressure and tidal stripping. We also carefully consider stellar mass loss in our model. When both mechanisms are included, the fraction of passive late types matches the data much more closely. However, the satellite over-quenching problem is still present in small galaxies in massive halos. In terms of the detectable residual star formation rates, gradual diffuse gas stripping appears to be much more important than stellar mass loss in our model. The implications of these results and other possibilities, such as redshift-dependent merging geometry and tidal disruption, are also discussed.</P>
The correlation of star formation quenching with internal galaxy properties and environment
Kimm, Taysun,Somerville, Rachel S.,Yi, Sukyoung K.,van den Bosch, Frank C.,Salim, Samir,Fontanot, Fabio,Monaco, Pierluigi,Mo, Houjun,Pasquali, Anna,Rich, R. M.,Yang, Xiaohu Blackwell Publishing Ltd 2009 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.394 No.3
<P>ABSTRACT</P><P>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 catalogue of Yang and collaborators, which is based on the Sloan Digital Sky Survey. Data from the Galaxy evolution explorer 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 are unable to conclude whether star formation quenching is primarily connected with halo mass or stellar mass, because these two quantities are themselves strongly correlated. 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 active galactic nuclei 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 <I>satellite overquenching problem</I> is caused by the too-rapid stripping of the satellites' hot gas haloes, which leads to rapid strangulation of star formation.</P>