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We summarize a study where we test the hypothesis that local black holes (BH) are relics of AGN activity. We compare the mass function of BHs in the local universe with that expected from AGN relics, which are BHs grown entirely with mass accretion during AGN phases. The local BH mass function (BHMF) is estimated by applying the well-known correlations between BH mass, bulge luminosity and stellar velocity dispersion to galaxy luminosity and velocity functions. The density of BHs in the local universe is . The relic BHMF is derived from the continuity equation with the only assumption that AGN activity is due to accretion onto massive BHs and that merging is not important. We find that the relic BHMF at =0 is generated mainly at <3. Moreover, the BH growth is anti-hierarchical in the sense that smaller BHs () grow at lower redshifts (<1) with respect to more massive ones (~ 1–3). Unlike previous works, we find that the BHMF of AGN relics is perfectly consistent with the local BHMF indicating the local BHs were mainly grown during AGN activity. This agreement is obtained while satisfying, at the same time, the constraints imposed by the X-ray background. The comparison with the local BHMF also suggests that the merging process is not important in shaping the relic BHMF, at least at low redshifts (<3). Our analysis thus suggests the following scenario: local BHs grew during AGN phases in which accreting matter was converted into radiation with efficiencies and emitted at a fraction = 0.1–1.7 of the Eddington luminosity. The average total lifetime of these active phases ranges from ≃ 4.5× 10 yr for to yr for .

I present a new method to unveil the history of cosmic accretion and the build-up of Supermassive Black Holes (SMBH) in the nuclei of galaxies, based on observations of the evolving radio and (hard) X-ray luminosity functions of AGN. The fundamental plane of black hole activity discovered by Merloni, Heinz & Di Matteo (2003) is used as a mass and accretion rate estimator. I adopt the local BH mass function as a boundary condition to integrate backwards in time the continuity equation for the SMBH evolution, neglecting the role of mergers. Under the most general assumption that accretion proceeds in a radiatively efficient way above a certain rate, and in a radiatively inefficient way below, the redshift evolution of the mass and accretion rate functions are calculated self-consistently. The only tunable parameters are the accretion efficiency and the critical ratio of the X-ray to Eddington luminosity at which the transition between accretion modes takes place. The evolution of the BH mass function between =0 and ~ 3 shows clear signs of an anti-hierarchical behaviour: while the majority of the most massive objects () were already in place at ~ 3, lower mass ones mainly grew at progressively lower redshift. As an example, I will discuss the consequences of these results for the lifetimes of accreting black holes.

Recent progress in reverberation mapping [5,10] enable the conversion of source luminosity and line-width into black hole (BH) mass () and accretion rate (; this is assumed to be proportional to /) (e.g. [8], [12] - hereafter S04). This allows the construction of the “BH mass function” of AGN which is a more physically meaningful concept compares with the usual luminosity function [3]. There are several far reaching consequences for fundamental cosmological questions like the comparison of BH growth-rate with galaxy evolution and the metal enrichment in the universe.

We use data of the CDFN 2Ms survey and related multi-wavelength observations to investigate the nature of the intrinsic SEDs of AGN, how they vary with redshift and luminosity, and how the data are affected by obscuration and possible contributions from starbursts. We believe that shifting observational data to the emitted frame provides a direct way to visualize effects of obscuration and changes in the underlying SED from object to object.

The formation and growth of supermassive black holes (SMBHs) physically related with bulges are considered. We focus on the radiation hydrodynamic process for the growth of SMBH in the optically thick starburst galaxies. In the present scenario, it is predicted that a host luminosity-dominant “proto-QSO phase” exists as a growing BH phase before the QSO phase, and the proto-QSO phase is preceded by an optically-thick ultraluminous infrared galaxy (ULIRG) phase.

We have recently ([1]) performed an all-sky survey in the 3-20 keV band from the data accumulated during satellite slews in 1996-2002 - the RXTE slew survey (XSS). For 90% of the sky at ||>10° , a flux limit for source detection of 2.5×10 erg/s/sq.cm(3-20 keV) or lower was achieved, while a combined area of 7000 sq.deg was sampled to record flux levels (for such very large-area surveys) below 10 erg/s/sq.cm. A catalog contains 294 X-ray sources. 236 of these sources were identified with a single known astronomical object. Of particular interest are 100 identified active galactic nuclei (AGNs) and 35 unidentified sources. The hard spectra of the latter suggest that many of them will probably also prove AGNs when follow-up observations are performed. Most of the detected AGNs belong to the local population (z<0.1). In addition, the hard X-ray band of the XSS (3-20 keV) as compared to most previous X-ray surveys, performed at photon energies below 10 keV, has made possible the detection of a substantial number of X-ray absorbed AGNs (mostly Seyfert 2 galaxies). These properties make the XSS sample of AGNs a valuable one for the study of the local population of AGNs. We carried out a thorough statistical analysis of the above sample in order to investigate several key properties of the local population of AGNs, in particular their distribution in intrinsic absorption column density (NH) and X-ray luminosity function ([2]). Knowledge of these characteristics provides important constraints for AGN unification models and synthesis of the cosmic X-ray background, and is further needed to understand the details of the accretion-driven growth of supermassive black holes in the nuclei of galaxies.

We present a new estimate of the local super-massive black hole (SMBH) mass function and show that it can be fully accounted for by the mass accreted during the luminous phases of X-ray selected active galactic nuclei (AGN) with a radiative efficiency of ~ 10%. The AGN visibility times grow with SMBH relic mass and are generally in the range ≥ 0.1–0.3 Gyr.

Based on a co-evolution scenario of massive black holes (MBH) and their host spheroids, we trace the BH growth and the joint cosmic star formation history by ROSAT X-ray All sky surveys. We found: 1) the total amount of star formation associated with MBH growth is at least half of the net star formation at high redshift, which probably missed by the current UV/opt. deep surveys; 2) an upper limit of the abundance ratio of type 2 to type 1 QSOs is about 2, within the constraints of the local BH density, the Chandra hard x-ray deep surveys and the SCUBA counts; 3)the peak redshift of the massive spheroid formation in this case is around 1.5-2.

A brief overview is presented of some aspects of the study of the growth of massive black holes in active galactic nuclei. It is argued that relativistic effects described by the Kerr solution of a spinning black hole are essential and are responsible for the formation of relativistic jets. It is further asserted that when the mass accretion rate is much larger and much smaller than the Eddington rate, the accretion is adiabatic and accompanied by prodigious outflows, ultimately driven by the energy flow through the disk associated with the magnetic torque. It is conjectured that this torque is dictated by the magnetic conditions at large radius and that, typically, there is preferred radial polarity in the magnetic field that joins the disk along with freshly accreted gas at its outer boundary. The associated magnetic flux is concentrated by the inflowing gas and soon becomes dynamically dominant so that it escapes the disk, driving an MHD wind. The radial field persists all the way down to the event horizon of the black hole and supplies a large flux to the hole when the disk is thick. Consequently, rapidly spinning holes accreting rapidly or slowly should be accompanied by relativistic jets which spin down the hole. The disks associated with intermediate accretion rates should be relatively thin and spin up the hole without forming powerful jets. This model provides a qualitative interpretation of the observed cosmological evolution of AGN, whereby the black holes that form later, lose the competition with star formation and grow to smaller masses. The co-evolution of black holes and their host galaxies is briefly discussed along with the impact on the intergalactic medium.