The Dependence of the Mean Spectral Energy Distributions on the Accretion Rate for Quasars with $z<0.75$ from the Sloan Digital Sky Survey

Abstract

We construct mean spectral energy distributions (SEDs) for a substantial sample of 56,969 Sloan Digital Sky Survey DR16 quasars with $z<0.75$, utilizing multiwavelength data from the mid-infrared (MIR) to ultraviolet (UV). These SEDs are built on eigenvector 1 parameters -- the relative optical $\mathrm{Fe}\mathrm{II}$ strength ($R_{\mathrm{Fe}\mathrm{II}}$) and the H$\beta$ line width ($\mathrm{H}\beta$) -- that capture the principal spectral variance of quasar spectra. From three $R_{\mathrm{Fe}\mathrm{II}}$-dependent mean SEDs we find that quasars with a larger $R_{\mathrm{Fe}\mathrm{II}}$ exhibit redder UV and optical and redder MIR and near-infrared (NIR) continua, indicating more dust emission. We also split our sample directly into Eddington ratio $L_{\mathrm{Bol}}/L_{\mathrm{Edd}}$ (or dimensionless accretion rate $\dot{\mathcal{M}}$) bins to construct different mean SEDs and find that the continua become increasingly red with increasing $L_{\mathrm{Bol}}/L_{\mathrm{Edd}}$ (or $\dot{\mathcal{M}}$) in the MIR, NIR, and UV bands. This demonstrates that the shapes of Type 1 AGN SEDs depend on the accretion rate. However, the optical continuum shows the opposite trend (becoming harder and bluer), indicating the complexity of the optical emission region. From $\mathrm{FWH}{\mathrm{M}}_{\mathrm{H}\beta }$-dependent mean SEDs we find that quasars with a larger $\mathrm{FWH}{\mathrm{M}}_{\mathrm{H}\beta }$ show redder optical and NIR continua and bluer UV and MIR continua. The bluer MIR continuum suggests that a larger angle between of the line of sight and the torus plane results in weaker torus emission in the MIR.

24 pages, 8 figures, Accepted for publication in ApJS