Mid-Infrared Selected Quasars I: Virial Black Hole Mass and Eddington Ratios

TL;DR

This paper presents a catalog of 391 mid-infrared-selected broad-emission-line quasars, analyzing their black hole masses and accretion rates, revealing trends like SMBH downsizing and constant Eddington ratios across redshifts.

Contribution

It provides a new MIR-selected quasar catalog extending SDSS coverage, including extended sources, and investigates their black hole properties and accretion behaviors.

Findings

SMBH mass shows evidence of downsizing.

Eddington ratios remain constant at 1 < z < 4.

Extended sources at z < 1 have lower Eddington ratios.

Abstract

We provide a catalog of 391 mid-infrared-selected (MIR, 24$\mu$m) broad-emission-line (BEL, type 1) quasars in the 22 deg$^2$ SWIRE Lockman Hole field. This quasar sample is selected in the MIR from Spitzer MIPS with $S_{\rm 24} > 400\mu$Jy, jointly with an optical magnitude limit of r (AB) $<$ 22.5 for broad line identification. The catalog is based on MMT and SDSS spectroscopy to select BEL quasars, extends the SDSS coverage to fainter magnitudes and lower redshifts, and recovers a more complete quasar population. The MIR-selected quasar sample peaks at $z\sim$1.4, and recovers a significant and constant (20\%) fraction of extended objects with SDSS photometry across magnitudes, which was not included in the SDSS quasar survey dominated by point sources. This sample also recovers a significant population of $z < 3$ quasars at $i > 19.1$. We then investigate the continuum luminosity and line profiles of these MIR quasars, and estimate their virial black hole masses and the Eddington ratios. The SMBH mass shows evidence of downsizing, though the Eddington ratios remain constant at $1 < z < 4$. Compared to point sources in the same redshift range, extended sources at $z < 1$ show systematically lower Eddington ratios. The catalog and spectra are publicly available online.