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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>
The Horizon-AGN simulation: morphological diversity of galaxies promoted by AGN feedback
Dubois, Yohan,Peirani, Sé,bastien,Pichon, Christophe,Devriendt, Julien,Gavazzi, Raphaë,l,Welker, Charlotte,Volonteri, Marta Oxford University Press 2016 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.463 No.4
Cosmic evolution of stellar quenching by AGN feedback: clues from the Horizon-AGN simulation
Beckmann, R. S.,Devriendt, J.,Slyz, A.,Peirani, S.,Richardson, M. L. A.,Dubois, Y.,Pichon, C.,Chisari, N. E.,Kaviraj, S.,Laigle, C.,Volonteri, M. Oxford University Press 2017 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.472 No.1
<P>The observed massive end of the galaxy stellar mass function is steeper than its predicted dark matter halo counterpart in the standard Lambda cold dark matter paradigm. In this paper, we investigate the impact of active galactic nuclei (AGN) feedback on star formation in massive galaxies. We isolate the impact of AGN by comparing two simulations from the HORIZON suite, which are identical except that one also includes supermassive black holes (SMBHs) and related feedback models. This allows us to cross-identify individual galaxies between simulations and quantify the effect of AGN feedback on their properties, including stellar mass and gas outflows. We find that massive galaxies (M-* >= 10(11) M-circle dot) are quenched by AGN feedback to the extent that their stellar masses decrease by up to 80 per cent at z = 0. SMBHs affect their host halo through a combination of outflows that reduce their baryonic mass, particularly for galaxies in the mass range 10(9) M-circle dot <= M-* <= 10(11) M-circle dot, and a disruption of central gas inflows, which limits in situ star formation. As a result, net gas inflows on to massive galaxies, M-* >= 10(11) M-circle dot, drop by up to 70 per cent. We measure a redshift evolution in the stellar mass ratio of twin galaxies with and without AGN feedback, with galaxies of a given stellar mass showing stronger signs of quenching earlier on. This evolution is driven by a progressive flattening of the M-SMBH-M-* relation with redshift, particularly for galaxies with M-* <= 10(10) M-circle dot. M-SMBH/M-* ratios decrease over time, as falling average gas densities in galaxies curb SMBH growth.</P>