Reaching the Peak of the quasar spectral energy distribution - II. Exploring the accretion disc, dusty torus and host galaxy

TL;DR

This study analyzes the spectral energy distributions of 11 AGN at redshifts 1.5-2.2, exploring accretion disc, dusty torus, and host galaxy properties, with implications for black hole spin, disc size, and galaxy relationships.

Contribution

It extends previous work by quantifying uncertainties, testing black hole spin effects, constraining disc radii, and modeling mid-IR components with physical parameters.

Findings

Outer accretion disc radii are about five times smaller than self-gravity radii.

Host galaxy luminosities align with the M_BH-bulge relationship.

Torus properties suggest a silicate grain composition.

Abstract

We continue our study of the spectral energy distributions (SEDs) of 11 AGN at 1.5 < z < 2.2, with optical-NIR spectra, X-ray data and mid-IR photometry. In a previous paper we presented the observations and models; in this paper we explore the parameter space of these models. We first quantify uncertainties on the black hole masses (M$_{\rm BH}$) and degeneracies between SED parameters. The effect of BH spin is tested, and we find that while low to moderate spin values (a$_*$ $\leq$ 0.9) are compatible with the data in all cases, maximal spin (a$_*$ = 0.998) can only describe the data if the accretion disc is face-on. The outer accretion disc radii are well constrained in 8/11 objects, and are found to be a factor ~5 smaller than the self-gravity radii. We then extend our modelling campaign into the mid-IR regime with WISE photometry, adding components for the host galaxy and dusty torus. Our estimates of the host galaxy luminosities are consistent with the M$_{\rm BH}$-bulge relationship, and the measured torus properties (covering factor and temperatures) are in agreement with earlier work, suggesting a predominantly silicate-based grain composition. Finally, we deconvolve the optical-NIR spectra using our SED continuum model. We claim that this is a more physically motivated approach than using empirical descriptions of the continuum such as broken power-laws. For our small sample, we verify previously noted correlations between emission linewidths and luminosities commonly used for single-epoch M$_{\rm BH}$ estimates, and observe a statistically significant anti-correlation between [O III] equivalent width and AGN luminosity.