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Suppression of star formation in early-type galaxies by feedback from supermassive black holes
Schawinski, Kevin,Khochfar, Sadegh,Kaviraj, Sugata,Yi, Sukyoung K.,Boselli, Alessandro,Barlow, Tom,Conrow, Tim,Forster, Karl,Friedman, Peter G.,Martin, D. Chris,Morrissey, Patrick,Neff, Susan,Schimino Nature Publishing Group 2006 Nature Vol.442 No.7105
Detailed high-resolution observations of the innermost regions of nearby galaxies have revealed the presence of supermassive black holes. These black holes may interact with their host galaxies by means of ‘feedback’ in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to observed relations between the black hole and the host. Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies.
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>
Galaxy Zoo: a sample of blue early-type galaxies at low redshift<sup>★</sup>
Schawinski, Kevin,Lintott, Chris,Thomas, Daniel,Sarzi, Marc,Andreescu, Dan,Bamford, Steven P.,Kaviraj, Sugata,Khochfar, Sadegh,Land, Kate,Murray, Phil,Nichol, Robert C.,Raddick, M. Jordan,Slosar, An Blackwell Publishing Ltd 2009 Monthly notices of the Royal Astronomical Society Vol.396 No.2
<P>ABSTRACT</P><P>We report the discovery of a population of nearby, blue early-type galaxies with high star formation rates (0.5 < SFR < 50 M<SUB>⊙</SUB> yr<SUP>−1</SUP>). They are identified by their visual morphology as provided by Galaxy Zoo for Sloan Digital Sky Survey Data Release 6 and their <I>u</I>−<I>r</I> colour. We select a volume-limited sample in the redshift range 0.02 < <I>z</I> < 0.05, corresponding to luminosities of approximately <I>L</I>* and above and with <I>u</I>−<I>r</I> colours significantly bluer than the red sequence. We confirm the early-type morphology of the objects in this sample and investigate their environmental dependence and star formation properties. Blue early-type galaxies tend to live in lower density environments than ‘normal’ red sequence early-types and make up 5.7 ± 0.4 per cent of the low-redshift early-type galaxy population. We find that such blue early-type galaxies are virtually absent at high velocity dispersions above 200 km s<SUP>−1</SUP>. Our analysis uses emission line diagnostic diagrams and we find that ∼25 per cent of them are actively star forming, while another ∼25 per cent host both star formation and an active galactic nucleus (AGN). Another ∼12 per cent are AGN. The remaining 38 per cent show no strong emission lines. When present and uncontaminated by an AGN contribution, the star formation is generally intense. We consider star formation rates derived from Hα, <I>u</I> band and infrared luminosities, and radial colour profiles, and conclude that the star formation is spatially extended. Of those objects that are not currently undergoing star formation must have ceased doing so recently in order to account for their blue optical colours. The gas-phase metallicity of the actively star-forming blue early-types galaxies is supersolar in all cases. We discuss the place of these objects in the context of galaxy formation. A catalogue of all 204 blue early-type galaxies in our sample, including star formation rates, emission line classification is provided.</P>