Star Formation Black Hole Growth and Dusty Tori in the Most Luminous Agns at Z = 2–3.5

Abstract

We report Herschel/SPIRE observations of 100 very luminous, optically selected active galactic nuclei (AGNs) at z 2 3.5 -= with log L 1350 (ergs −1 ) 46.5 , where L 1350 is λL λ at 1350 Å. The distribution in L 1350 is similar to the general distribution of Sloan Digital Sky Survey AGNs in this redshift and luminosity interval. We measured starformation (SF) luminosity, L SF , and SF rate (SFR) in 34 detected sources by fitting combined SF and torus templates, where the torus emission is based on Wide Field Infrared Survey Explorer observations. We also obtained statistically significant stacks for the undetected sources in two luminosity groups. The sample properties are compared with those of very luminous AGNs at z 4. M e yr −1 , respectively. The mean SFR of the undetected sources is 148 M e yr −1 . The ratio of SFR to the black hole accretion rate is ≈80 for the detected sources and less than 10 for the undetected sources. Unlike a sample of sources at z ; 4.8 that we studied recently, there is no difference in L AGN and only a very small difference in L torus between the detected and undetected sources. (2) The redshift distribution of L SF and L AGN for the most luminous, redshift 2-7 AGNs are different. Similar to previous studies, the highest L AGN are found at z ≈ 3. However, the L SF of such sources peaks at z ≈ 5. Assuming the objects in our sample are hosted by the most massive galaxies at those redshifts, we find that approximately 2/3 of the hosts are already below the main sequence of SF galaxies at z = 2−3.5. (3) The spectral energy distributions (SEDs) of dusty tori at high redshift are similar to the shapes found in low redshift, low luminosity AGNs. Herschel upper limits put strong constraints on the long wavelength shape of the SED, ruling out several earlier suggested torus templates as applicable for this sample. (4) We find no evidence for a luminosity dependence of the torus covering factor in sources with log L AGN (ergs −1 ) = 44−47.5. This conclusion is based on the recognition that the estimated L AGN in several earlier studies is highly uncertain and non-uniformally treated. The median covering factors over this range are 0.68 for isotropic dust emission and 0.4 for anisotropic emission.

Stellar Mass Function of Active and Quiescent Galaxies via the Continuity Equation

“…As to the quenching timescale, the observed fraction of far-IR detected host galaxies in X-ray (e.g., Mullaney et al 2012;Page et al 2012;Rosario et al 2012;Barger et al 2015;Stanley et al 2015;Harrison et al 2016) and optically selected AGNs (e.g., Mor et al 2012;Wang et al 2013;Willott et al 2015;Xu et al 2015;Netzer et al 2016;Harris et al 2016) points toward a SFR abruptly stopping, at least in massive galaxies, after τ sphe over a short timescale 10 8 yr due to the action of feedbacks (see Lapi et al 2014). To avoid introducing an additional parameter, in Eq.…”

The Intrinsic Far-infrared Continua of Type-1 Quasars

“…To measure the IR star formation rates (SFRs) of quasar host galaxies, a proper handling of the AGN far-IR contribution is critical. A number of papers have analyzed the quasar IR SEDs with a combination of the SED library from some torus model and templates/models for the host galaxies, and derived the host SFRs from the IR luminosities of the latter component (e.g., Delvecchio et al 2014;Leipski et al 2014;Dong & Wu 2016;Netzer et al 2016). However, since none of the torus models have been observationally well constrained in the far-IR, the accuracy of the SFR measurements is not always guaranteed, even if the fitting residuals are tiny.…”

Black Hole Growth Is Mainly Linked to Host-galaxy Stellar Mass Rather Than Star Formation Rate

“…Observations reveal a linear correlation between star formation rate (SFR) and sample-averaged black hole accretion rate (á ñ BHAR ) for star-forming galaxies (e.g., Chen et al 2013, hereafter C13). Also, X-ray-selected active galactic nuclei (AGNs) preferentially reside in star-forming rather than quiescent galaxies for samples with matched stellar mass ( * M ; e.g., Rosario et al 2013), and optically selected luminous quasars tend to be hosted by strongly star-forming systems (e.g., Harris et al 2016;Netzer et al 2016). However, the sample-averaged SFR (á ñ SFR ) of the host galaxies of X-ray AGNs does not show a significant dependence on the BHAR in the regimes of low and moderate AGN luminosity, while the potential existence of a positive SFR-BHAR relation at high luminosities is still debatable (e.g., Harrison et al 2012;Rosario et al 2012;Barger et al 2015;Stanley et al 2015).…”