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The population of supermassive black holes (SMBHs) is composed by quiescent SMBHs, such as those seen in local galaxies including the Milky Ways, and active ones, resulting in quasars and active galactic nuclei (AGN). Outside our neighbourhood, all the information we have on SMBHs is derived from quasars and AGN, giving us a partial view. We study the evolution of the SMBH population, total and active, by the continuity equation, backwards in time from z=0 to z=4. Type-1 and type-2 AGN are differentiated in the model on the basis of the Eddington ratio distribution, chosen on the basis of observational estimates. The duty cycle is obtained by matching the luminosity function of quasars, and the average radiative efficiency is the only free parameter in the model. For higher radiative efficiencies (>~0.07) a large fraction of the SMBH population, most of them quiescent, must already be in place by z=4. For lower radiative efficiencies (~0.05), the duty cycle increases with the redshift and the SMBH population evolves dramatically since z=4. The mass function of active SMBHs does not depend on the choice of the radiative efficiency or of the local SMBH mass function, but it is mainly determined by the quasar luminosity function, once the Eddington ratio distribution is fixed. Only a direct measurement of the total BHMF at redshifts z>~2 could break these degeneracies giving important constraints on the average radiative efficiency. Focusing on type-1 AGN, for which observational estimates of the mass function and Eddington ratio distribution exist at various redshift, models with lower radiative efficiencies reproduce better the high-mass end of the mass function at high-z, but they tend to over-predict it at low-z, and vice-versa for models with higher radiative efficiencies.
The next generation of electromagnetic and gravitational wave observatories will open unprecedented windows to the birth of the first supermassive black holes. This has the potential to reveal their origin and growth in the first billion years, as we
The triggering mechanisms for Active Galactic Nuclei (AGN) are still debated. Some of the most popular ones include galaxy interactions (IT) and disk instabilities (DI). Using an advanced semi analytic model (SAM) of galaxy formation, coupled to accu
We summarize what large surveys of the contemporary universe have taught us about the physics and phenomenology of the processes that link the formation and evolution of galaxies and their central supermassive black holes. We present a picture in whi
By examining the locations of central black holes in two elliptical galaxies, M,32 and M,87, we derive constraints on the violation of the strong equivalence principle for purely gravitational objects, i.e. black holes, of less than about two-thirds,
We carry out a comprehensive Bayesian correlation analysis between hot halos and direct masses of supermassive black holes (SMBHs), by retrieving the X-ray plasma properties (temperature, luminosity, density, pressure, masses) over galactic to cluste