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

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${}_{\mathrm{BH}}$) and degeneracies between SED parameters. The effect of BH spin is tested, and we find that while low to moderate spin values (a${}_{\ast }$ $\le$ 0.9) are compatible with the data in all cases, maximal spin (a${}_{\ast }$ = 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${}_{\mathrm{BH}}$-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${}_{\mathrm{BH}}$ estimates, and observe a statistically significant anti-correlation between [O III] equivalent width and AGN luminosity.

26 pages, 19 figures, 5 tables; accepted for publication in MNRAS

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