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

Abstract

We provide a catalog of 391 mid-infrared-selected (MIR; 24 μm) 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 24 > 400 μJy, jointly with an optical magnitude limit of r (AB) < 22.5 for broad line identification. The catalog is based on MMT and Sloan Digital Sky Survey (SDSS) spectroscopy to select BEL quasars, extending the SDSS coverage to fainter magnitudes and lower redshifts, and recovers a more complete quasar population. The MIR-selected quasar sample peaks at z ∼ 1.4 and recovers a significant and constant (20%) fraction of extended objects with SDSS photometry across magnitudes, which were 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 supermassive black hole mass shows evidence of downsizing, although 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.

Is there a relationship between AGN and star formationin IR-bright AGNs?

“…The selection criteria in X15 is comparable to our sample as both require detections in X-ray and FIR, except that X15 has an additional selection based on MIPS 24µ m flux. The 24µ m flux selection is highly complete for AGNs (Krawczyk et al 2013;Dai et al 2014), which is again confirmed by the similar fitting results.…”

“…On the other hand, SMBH mass is well-known to decrease to-wards lower redshift in optical type 1 AGNs (e.g. Labita et al 2009;Dai et al 2014). The mass downsizing effect would result in higher L AGN at high z, as demonstrated earlier in Figure. 2.…”

“…Since the ERs of AGNs are not evolving significantly between the present day and z =4 (e.g. Dai et al 2014), the observed relations in the ER are not redshift effects. On the other hand, SMBH mass is well-known to decrease to-wards lower redshift in optical type 1 AGNs (e.g.…”

“…The remaining 795 objects have no z estimate due to the non-uniform multi-wavelength coverage of the field. We did not limit our sample to pointsources, as extended morphologies have also been reported to be common in IR-detected quasars (Dai et al 2014). For 50% (1,190) of the hard X-ray targets, spectroscopic redshifts (spec-z) are available from a. the SDSS-BOSS DR12 6 catalog (943, within a matching radius of 6 ′′ ); b. various publications (229 7 , for detailed list of reference see Melnyk et al (2013), M13); c. an MMT-Hectospec redshift survey based on 24µm priors (18, a similar survey is described in detail in Dai et al (2014)).…”

Composite Spectral Energy Distributions and Infrared–Optical Colors of Type 1 and Type 2 Quasars

“…Such obscured ("type 2") active galactic nuclei (AGNs) can be identified from narrow optical emission lines (Zakamska et al 2003(Zakamska et al , 2004(Zakamska et al , 2005Reyes et al 2008;Yuan et al 2016), radio luminosity (e.g., McCarthy 1993Martínez-Sansigre et al 2006;Seymour et al 2007;Wilkes et al 2013), or X-ray properties (e.g Alexander et al 2001;Stern et al 2002;Treister et al 2004;Vignali et al 2006Vignali et al , 2009Del Moro et al 2014). In addition, pioneering work with the Spitzer Space Telescope demonstrated that obscured quasars have similar mid-infrared (MIR) SEDs to their unobscured counterparts but are dominated by host galaxy light in the optical (Lacy et al 2004;Rowan-Robinson et al 2005;Stern et al 2005;Alonso-Herrero et al 2006;Martínez-Sansigre et al 2006;Polletta et al 2006;Hickox et al 2007;Donley et al 2008;Lacy et al 2013Lacy et al , 2015Dai et al 2014). Consequently, obscured quasars can be most efficiently selected in the MIR, as they appear very red in the IRAC [3.6] -[4.5] color, characteristic of the "hot" MIR SED that is evident in broadline quasars (e.g., Richards et al 2006;Assef et al 2010, hereafter R06 and A10, respectively).…”