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DESTRUCTION OF MOLECULAR GAS RESERVOIRS IN EARLY-TYPE GALAXIES BY ACTIVE GALACTIC NUCLEUS FEEDBACK
Schawinski, Kevin,Lintott, Chris J.,Thomas, Daniel,Kaviraj, Sugata,Viti, Serena,Silk, Joseph,Maraston, Claudia,Sarzi, Marc,Yi, Sukyoung K.,Joo, Seok-Joo,Daddi, Emanuele,Bayet, Estelle,Bell, Tom,Zuntz, IOP Publishing 2009 The Astrophysical journal Vol.690 No.2
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>
Martin, G,Kaviraj, S,Volonteri, M,Simmons, B D,Devriendt, J E G,Lintott, C J,Smethurst, R J,Dubois, Y,Pichon, C Oxford University Press 2018 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.476 No.2
<P>Understanding the processes that drive the formation of black holes (BHs) is a key topic in observational cosmology. While the observed M-BH-M-Bulge correlation in bulge-dominated galaxies is thought to be produced by major mergers, the existence of an M-BH-M star relation, across all galaxy morphological types, suggests that BHs may be largely built by secular processes. Recent evidence that bulge-less galaxies, which are unlikely to have had significant mergers, are offset from the M-BH-M-Bulge relation, but lie on the MBH-M star relation, has strengthened this hypothesis. Nevertheless, the small size and heterogeneity of current data sets, coupled with the difficulty in measuring precise BH masses, make it challenging to address this issue using empirical studies alone. Here, we use Horizon-AGN, a cosmological hydrodynamical simulation to probe the role of mergers in BH growth over cosmic time. We show that (1) as suggested by observations, simulated bulge-less galaxies lie offset from the main MBH-MBulge relation, but on the M-BH-M star relation, (2) the positions of galaxies on the M-BH-M star relation are not affected by their merger histories, and (3) only similar to 35 per cent of the BH mass in today's massive galaxies is directly attributable to merging - the majority (similar to 65 per cent) of BH growth, therefore, takes place gradually, via secular processes, over cosmic time.</P>