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Register a new userThe big picture of AGN feedback: Black hole accretion and galaxy evolution in multiwavelength surveys
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Ryan C. Hickox
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Large extragalactic surveys allow us to trace, in a statistical sense, how supermassive black holes, their host galaxies, and their dark matter halos evolve together over cosmic time, and so explore the consequences of AGN feedback on galaxy evolution. Recent studies have found significant links between the accretion states of black holes and galaxy stellar populations, local environments, and obscuration by gas and dust. This article describes some recent results and shows how such studies may provide new constraints on models of the co-evolution of galaxies and their central SMBHs. Finally, I discuss observational prospects for the proposed Wide-Field X-ray Telescope mission.
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We describe a physical model of the outflows produced as a result of gas accretion onto a black hole, and the resultant changes to star formation rates and efficiencies in galaxies, using the Radio-SAGE semi-analytic galaxy formation model. We show that the ratio of outflow rate to SFR of galaxies is mainly driven by black hole mass and virial halo mass, and show that the SFR is higher than the outflow rate at low black hole masses. The model consistently reproduces the observed evolution of star formation rate density from z = 6 to z = 0, as well as the trend of the stellar mass - halo mass relations. We show the characteristic growth of massive galaxies influenced by AGN feedback at different redshifts. We find feedback to be prevalent in the most massive galaxy halos, inhibiting the cooling catastrophe.
Recent models of super-massive black hole (SMBH) and host galaxy joint evolution predict the presence of a key phase where accretion, traced by obscured Active Galactic Nuclei (AGN) emission, is coupled with powerful star formation. Then feedback processes likely self-regulate the SMBH growth and quench the star-formation activity. AGN in this important evolutionary phase have been revealed in the last decade via surveys at different wavelengths. On the one hand, moderate-to-deep X-ray surveys have allowed a systematic search for heavily obscured AGN, up to very high redshifts (z~5). On the other hand, infrared/optical surveys have been invaluable in offering complementary methods to select obscured AGN also in cases where the nuclear X-ray emission below 10 keV is largely hidden to our view. In this review I will present my personal perspective of the field of obscured accretion from AGN surveys.
Various observational techniques have been used to survey galaxies and AGN, from X-rays to radio frequencies, both photometric and spectroscopic. I will review these techniques aimed at the study of galaxy evolution and of the role of AGNs and star formation as the two main energy production mechanisms. I will then present as a new observational approach the far-IR spectroscopic surveys that could be done with planned astronomical facilities of the next future, such as SPICA from the space and CCAT from the ground.
We use a semi-analytic galaxy formation model to study the co-evolution of supermassive black holes (SMBHs) with their host galaxies. Although the coalescence of SMBHs is not important, the quasar-mode accretion induced by mergers plays a dominant role in the growth of SMBHs. Mergers play a more important role in the growth of SMBH host galaxies than in the SMBH growth. It is the combined contribution from quasar mode accretion and mergers to the SMBH growth and the combined contribution from starburst and mergers to their host galaxy growth that determine the observed scaling relation between the SMBH masses and their host galaxy masses. We also find that mergers are more important in the growth of SMBH host galaxies compared to normal galaxies which share the same stellar mass range as the SMBH host galaxies.
We present a new backward evolution model for galaxies and AGNs in the infrared (IR). What is new in this model is the separate study of the evolutionary properties of the different IR populations (i.e. spiral galaxies, starburst galaxies, low-luminosity AGNs, unobscured type 1 AGNs and obscured type 2 AGNs) defined through a detailed analysis of the spectral energy distributions (SEDs) of large samples of IR selected sources. The evolutionary parameters have been constrained by means of all the available observables from surveys in the mid- and far-IR (source counts, redshift and luminosity distributions, luminosity functions). By decomposing the SEDs representative of the three AGN classes into three distinct components (a stellar component emitting most of its power in the optical/near-IR, an AGN component due to hot dust heated by the central black hole peaking in the mid-IR, and a starburst component dominating the far-IR spectrum) we have disentangled the AGN contribution to the monochromatic and total IR luminosity emitted by the different populations considered in our model from that due to star-formation activity. We have then obtained an estimate of the total IR luminosity density (and star-formation density - SFD - produced by IR galaxies) and the first ever estimate of the black hole mass accretion density (BHAR) from the IR. The derived evolution of the BHAR is in agreement with estimates from X-rays, though the BHAR values we derive from IR are slightly higher than the X-ray ones. Finally, we have simulated source counts, redshift distributions and SFD and BHAR that we expect to obtain with the future cosmological Surveys in the mid-/far-IR that will be performed with JWST-MIRI and SPICA-SAFARI.
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