The Accretion History of AGN: The Spectral Energy Distributions of X-ray Luminous AGN

Abstract

Spectral energy distributions (SEDs) from X-ray to far-infrared (FIR) wavelengths are presented for a sample of 1246 X-ray luminous active galactic nuclei (AGN; $L_{0.5-10\mathrm{keV}}>10^{43}$ erg s${}^{-1}$), with $z_{\mathrm{spec}}<1.2$, selected from Stripe 82X, COSMOS, and GOODS-N/S. The rest-frame SEDs show a wide spread ($\sim 2.5$ dex) in the relative strengths of broad continuum features at X-ray, ultraviolet (UV), mid-infrared (MIR), and FIR wavelengths. A linear correlation (log-log slope of 0.7$\pm 0.04$) is found between $L_{\mathrm{MIR}}$ and $L_{\mathrm{X}}$. There is significant scatter in the relation between the $L_{\mathrm{UV}}$ and $L_{\mathrm{X}}$ due to heavy obscuration, however the most luminous and unobscured AGN show a linear correlation (log-log slope of 0.8$\pm 0.06$) in the relation above this scatter. The relation between $L_{\mathrm{FIR}}$ and $L_{\mathrm{X}}$ is predominantly flat, but with decreasing dispersion at $L_{\mathrm{X}}>10^{44}$ erg s${}^{-1}$. The ratio between the "galaxy subtracted" bolometric luminosity and the intrinsic $L_{\mathrm{X}}$ increases from a factor of $\sim$$10-70$ from log $L_{\mathrm{bol}}/{(\mathrm{erg}\mathrm{s}}^{-1})=44.5-46.5$. Characteristic SED shapes have been determined by grouping AGN based on relative strengths of the UV and MIR emission. The average $L_{1\hat{I}¼\mathrm{m}}$ is constant for the majority of these SED shapes, while AGN with the strongest UV and MIR emission have elevated $L_{1\hat{I}¼\mathrm{m}}$, consistent with the AGN emission dominating their SEDs at optical and NIR wavelengths. A strong correlation is found between the SED shape and both the $L_{\mathrm{X}}$ and $L_{\mathrm{bol}}$, such that $L_{\mathrm{bol}}/L_{\mathrm{X}}=20.4\pm 1.8$, independent of the SED shape. This is consistent with an evolutionary scenario of increasing $L_{\mathrm{bol}}$ with decreasing obscuration as the AGN blows away circumnuclear gas.

24 pages, 20 figures, 4 appendix tables, Accepted to ApJ