AGN host galaxy mass function in COSMOS

Is AGN feedback responsible for the mass-quenching of galaxies?

¹ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
e-mail: angela.bongiorno@oa-roma.inaf.it (OAR)
² Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, the University of Tokyo, 277-8583 Kashiwa, Japan (Kavli IPMU, WPI)
³ Max-Planck-Institut fuer Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
⁴ INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁵ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁶ Dipartimento di Matematica e Fisica, Università Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy
⁷ Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
⁸ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen, Germany
⁹ Dipartimento di Fisica e Astronomia, Università di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
¹⁰ California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125, USA

Received: 23 September 2015
Accepted: 5 January 2016

Abstract

We investigate the role of supermassive black holes in the global context of galaxy evolution by measuring the host galaxy stellar mass function (HGMF) and the specific accretion rate, that is, λ_SAR, the distribution function (SARDF), up to z ~ 2.5 with ~1000 X-ray selected AGN from XMM-COSMOS. Using a maximum likelihood approach, we jointly fit the stellar mass function and specific accretion rate distribution function, with the X-ray luminosity function as an additional constraint. Our best-fit model characterizes the SARDF as a double power-law with mass-dependent but redshift-independent break, whose low λ_SAR slope flattens with increasing redshift while the normalization increases. This implies that for a given stellar mass, higher λ_SAR objects have a peak in their space density at earlier epoch than the lower λ_SAR objects, following and mimicking the well-known AGN cosmic downsizing as observed in the AGN luminosity function. The mass function of active galaxies is described by a Schechter function with an almost constant M^∗_⋆ and a low-mass slope α that flattens with redshift. Compared to the stellar mass function, we find that the HGMF has a similar shape and that up to log (M_⋆/M_⊙) ~ 11.5, the ratio of AGN host galaxies to star-forming galaxies is basically constant (~10%). Finally, the comparison of the AGN HGMF for different luminosity and specific accretion rate subclasses with a previously published phenomenological model prediction for the “transient” population, which are galaxies in the process of being mass-quenched, reveals that low-luminosity AGN do not appear to be able to contribute significantly to the quenching and that at least at high masses, that is, M_⋆ > 10^10.7 M_⊙, feedback from luminous AGN (log L_bol ≳ 46 [erg/s]) may be responsible for the quenching of star formation in the host galaxy.