Mean Spectral Energy Distributions and Bolometric Corrections for Luminous Quasars

Abstract

We explore the mid-infrared (mid-IR) through ultraviolet (UV) spectral energy distributions (SEDs) of 119,652 luminous broad-lined quasars with 0.064 < z < 5.46 using mid-IR data from Spitzer and WISE, near-infrared data from Two Micron All Sky Survey and UKIDSS, optical data from Sloan Digital Sky Survey, and UV data from Galaxy Evolution Explorer. The mean SED requires a bolometric correction (relative to 2500Å) of BC 2500Å = 2.75 ± 0.40 using the integrated light from 1 µm-2 keV, and we further explore the range of bolometric corrections exhibited by individual objects. In addition, we investigate the dependence of the mean SED on various parameters, particularly the UV luminosity for quasars with 0.5 z 3 and the properties of the UV emission lines for quasars with z 1.6; the latter is a possible indicator of the strength of the accretion disk wind, which is expected to be SED dependent. Luminosity-dependent mean SEDs show that, relative to the highluminosity SED, low-luminosity SEDs exhibit a harder (bluer) far-UV spectral slope (α UV ), a redder optical continuum, and less hot dust. Mean SEDs constructed instead as a function of UV emission line properties reveal changes that are consistent with known Principal Component Analysis (PCA) trends. A potentially important contribution to the bolometric correction is the unseen extream-UV (EUV) continuum. Our work suggests that lower-luminosity quasars and/or quasars with disk-dominated broad emission lines may require an extra continuum component in the EUV that is not present (or much weaker) in high-luminosity quasars with strong accretion disk winds. As such, we consider four possible models and explore the resulting bolometric corrections. Understanding these various SED-dependent effects will be important for accurate determination of quasar accretion rates.

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

“…As a consistency check, the composite generated in this work is used to fit for the dust content of quasars with varying degree of extinction and consistent results were obtained as compared with composites generated from other subsamples of the parent population. For a comparison between SDSS and quasars detected in GALEX, UKIDSS, WISE, 2MASS and Spitzer, see Krawczyk et al (2013). Because of the high luminosity of the objects presented here, several differences in the properties are expected as compared to those of the global quasar population.…”

Quasars as standard candles

“…We used the SDSS photometry to compute, for each object, the slope Γ 1 of a log(ν) − log(νLν) power law in the rest frame 0.3-1 µm range, and the analogous slope Γ 2 in the 1450-3000 Å range. The wavelength coverage of the SDSS photometry does not cover the rest frame 1µm at z ∼ 2, we thus considered the mid-infrared data from Spitzer and WISE, and the near-infrared data from the Two Micron All Sky Survey and UKIDSS published by Krawczyk et al (2013) for the same SDSS-DR7 quasar sample. We selected all sources in the (Γ 1 , Γ 2 ) plane within a circle centred at the reference values for a standard SED of quasars (see Risaliti & Lusso 2015 and LR16 for further details) with a radius corresponding to a reddening E(B − V) 0.1.…”

Rapidly growing black holes and host galaxies in the distant Universe from theHerschelRadio Galaxy Evolution Project

“…Numerous attempts to derive bolometric correction factors have been done (e.g. Elvis et al 1994;Haas et al 2003;Marconi et al 2004;Krawczyk et al 2013;Hao et al 2014;Scott & Stewart 2014). Although essential, they are subject to significative variation from object to object.…”