The Coevolution of Supermassive Black Holes and Massive Galaxies at High Redshift

Abstract

We exploit the recent, wide samples of far-infrared (FIR) selected galaxies followed-up in X rays and of X-ray/optically selected active galactic nuclei (AGNs) followed-up in the FIR band, along with the classic data on AGN and stellar luminosity functions at high redshift z 1.5, to probe different stages in the coevolution of supermassive black holes (BHs) and host galaxies. The results of our analysis indicate the following scenario: (i) the star formation in the host galaxy proceeds within a heavily dust-enshrouded medium at an almost constant rate over a timescale 0.5 − 1 Gyr, and then abruptly declines due to quasar feedback; over the same timescale, (ii) part of the interstellar medium loses angular momentum, reaches the circum-nuclear regions at a rate proportional to the star formation and is temporarily stored into a massive reservoir/proto-torus wherefrom it can be promptly accreted; (iii) the BH grows by accretion in a self-regulated regime with radiative power that can slightly exceed the Eddington limit L/L Edd 4, particularly at the highest redshifts; (iv) for massive BHs the ensuing energy feedback at its maximum exceeds the stellar one and removes the interstellar gas, thus stopping the star formation and the fueling of the reservoir; (v) afterwards, if the latter has retained enough gas, a phase of supply-limited accretion follows exponentially declining with a timescale of about 2 e-folding times. We also discuss how the detailed properties and the specific evolution of the reservoir can be investigated via coordinated, high-resolution observations of starforming, strongly-lensed galaxies in the (sub-)mm band with ALMA and in the X-ray band with Chandra and the next generation X-ray instruments.

Hidden starbursts and active galactic nuclei at 0 < z < 4 from theHerschel-VVDS-CFHTLS-D1 field: Inferences on coevolution and feedback

“…Such a scenario is identical to that advocated by Gruppioni et al (2013) for the population most resembling the ULIRGs we consider here, in which the number counts of various types of Herschel sources across four fields were used, along with a variety of other evidence, to deduce the evolutionary scenario for galaxies with powerful coeval starburst and AGN activity. It is also similar to the model adopted to fit a compilation of Herschel observations of X-ray AGN hosts in Lapi et al (2014). The above scenario does not preclude the possibility of additional quenching occuring due to processes associated with the star formation itself (see, e.g., Cen 2012), processes which can be quite strong in galaxies with the typical SFRs of the ULIRGs in the full SPIRE sample.…”

“…This is not the first time this trend has been observed. In two different studies covering different fields, Kartaltepe et al (2010a) and Juneau et al (2013;hereafter J13) observed that the fraction of galaxies which host AGN, AGN selected by a wide variety of methods, was a strong function of L TIR (see also the review of this trend for galaxies hosting X-ray AGN in Lapi et al 2014). These samples were, however, selected at shorter wavelengths, meaning that the contamination to L TIR from the AGN was more problematic than it is in a SPIRE-selected sample.…”

“…The observed trend of increasing AGN fraction with increasing L TIR is a trend that would not be observed if the truncation process in the starburst took place over a long timescale. Such gradual quenching is also disfavored by modeling of Herschel-bright X-ray AGN hosts, in which the fraction of IR-bright starbursts amongst powerful X-ray AGN hosts is shown to be highly sensitive to the star-formation quenching timescale (Lapi et al 2014;compare, e.g., Figs. 10 and 12).…”

“…Given the efficiency of feedback mechanisms associated with luminous AGN at the peak of their activity (e.g., Harrison et al 2012a), it is natural to appeal to the AGN as the mechanism causing the cessation of star-formation activity in their ULIRG host galaxies. While a seemingly equally plausible scenario is one in which the AGN ceases its activity and, at the same time, the starburst strength drops to a lower level and continues to form stars in the absence of an AGN, the large number of both lowluminosity and powerful AGN observed with post-starburst features in their spectra or with transitional colors (Schawinski et al 2007;Georgakakis et al 2008;Hickox et al 2009;Kocevski et al 2009bKocevski et al , 2011bRumbaugh et al 2012) and the small fraction of X-ray AGN hosts detected in the FIR (see Lapi et al 2014 and references therein) strongly argues against this scenario. It still remains a possibility, however, that the power of the starburst and AGN decrease in tandem, with the AGN continuing to accrete matter, but emitting at a level below our detection limits.…”

Selection bias in dynamically measured supermassive black hole samples: its consequences and the quest for the most fundamental relation

“…In addition, it is possible that other processes such as dynamical friction and AGN feedback effects may contribute to the creation of cores in the inner regions of massive galaxies (e.g. A number of observations and black hole accretion models (e.g., Marconi et al 2004;Merloni 2004;Granato et al 2006;Lapi et al 2006;Zheng et al 2009;Silverman et al 2008;Shankar et al 2009b;Mullaney et al 2012;Lapi et al 2014) suggest some degree of correlation between black hole growth and large-scale star formation. On the other hand, a number of observational and theoretical studies are now showing that the actual coevolution may be more complex to probe observationally, possibly depending on the different evolutionary phases undergone by the host galaxies as well as AGN variability effects (e.g., Hickox et al 2014;Rodighiero et al 2015;Volonteri et al 2015;Graham 2016;Westhues et al 2016, and references therein).…”