The Optical–uv Emissivity of Quasars: Dependence on Black Hole Mass and Radio Loudness

Abstract

We analyzed a large sample of radio-loud and radio-quiet quasar spectra at redshift 1.0 ≤ z ≤ 1.2 to compare the inferred underlying quasar continuum slopes (after removal of the host galaxy contribution) with accretion disk models. The latter predict redder (decreasing) α 3000 continuum slopes (L ν ∝ ν α at 3000Å) with increasing black hole mass, bluer α 3000 with increasing luminosity at 3000Å, and bluer α 3000 with increasing spin of the black hole, when all other parameters are held fixed. We find no clear evidence for any of these predictions in the data. In particular we find that: (i) α 3000 shows no significant dependence on black hole mass or luminosity. Dedicated Monte Carlo tests suggest that the substantial observational uncertainties in the black hole virial masses can effectively erase any intrinsic dependence of α 3000 on black hole mass, in line with some previous studies. (ii) The mean slope α 3000 of radio-loud sources, thought to be produced by rapidly spinning black holes, is comparable to, or even redder than, that of radio-quiet quasars. Indeed, although quasars appear to become more radio loud with decreasing luminosity, we still do not detect any significant dependence of α 3000 on radio loudness. The predicted mean α 3000 slopes tend to be bluer than in the data. Disk models with high inclinations and dust extinction tend to produce redder slopes closer to empirical estimates. Our mean α 3000 values are close to the ones independently inferred at z < 0.5 suggesting weak evolution with redshift, at least for moderately luminous quasars.

Evidence for Higher Black Hole Spin in Radio-loud Quasars

“…This result is consistent with previous work that found RL quasars to be redder (Brotherton et al 2001;Labita et al 2008;Shankar et al 2016). We confirm this trend holds also when the samples are being matched in M BH , L 5100 and z.…”

Probing black hole accretion tracks, scaling relations, and radiative efficiencies from stacked X-ray active galactic nuclei

“…Most importantly, we find ( Figure 5) that reproducing the raw observed relation between galaxy stellar masses and the dynamically inferred masses of inactive black holes requires a radiative efficiency ε ∼ 0.02, well below theoretical expectations for thin accretion disks and values inferred from UV spectral energy distribution fitting (e.g., Davis & Laor 2011;Trakhtenbrot 2014;Capellupo et al 2015a;Shankar et al 2016b) and X-ray reflection analysis (Reynolds 2014). Higher bolometric corrections or significant fractions of obscured accretion can increase the inferred ε, but we still find ε 0.05 for reasonable assumptions about these uncertainties ( Figure 6).…”

“…A non-negligible obscured AGN fraction f for galaxies in our stellar mass range (e.g., Harrison et al 2016;Ananna et al 2019) would increase our inferred ε by a factor ∼ (1 + f ), so at face value our results favour ε 0.15 − 0.20, implying high characteristic spin parameters a 0.9. Most direct measurements of black hole spins from X-ray reflection spectroscopy favour a 0.5 (see, for example, Table 1 in Zhang & Lu 2019), a finding further corroborated by UV spectral energy distribution modelling (e.g., Capellupo et al 2015a;Shankar et al 2016b). Future observations and modelling can reduce uncertainties in bolometric corrections and the contribution of obscured accretion.…”

Continuum Reverberation Mapping of the Accretion Disks in Two Seyfert 1 Galaxies

“…It is also observationally difficult to isolate the intrinsic disk continuum due to line emission, host-galaxy starlight, and internal reddening, and the emission peak is generally unobservable due to absorption by intervening hydrogen. After accounting for these effects, it is sometimes possible to fit the observed spectrum with disk models (e.g., Capellupo et al 2015), but this is not always the case (e.g., Shankar et al 2016). Alternative attempts to isolate the continuum emission have made use of polarimetry (Kishimoto et al 2004(Kishimoto et al , 2008 and difference spectra/color variability (Wilhite et al 2005;Pereyra et al 2006;Schmidt et al 2012), but the interpretation of these data is not straightforward (e.g., Kokubo 2015Kokubo , 2016.…”