Optical Spectroscopy and X-Ray Detections of a Sample of Quasars and Active Galactic Nuclei Selected in the Mid-Infrared from Two Spitzer Space Telescope Wide-Area Surveys

By M. Lacy, A. Petric, A. Sajina, G. Canalizo, L. Storrie-Lombardi, Lee Armus, D. Fadda, F. Center, Caltech, Columbia University New York and 2 more. 2006

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We present optical spectroscopy of a sample of 77 luminous active galactic nuclei (AGNs) and quasars selected on the basis of their mid-infrared colors. Our objects are selected from the Spitzer Extragalactic First Look Survey and the SWIRE XMM-Newton Large-Scale Structure Survey (XMM-LSS) fields, with a typical 24 μm flux density of 5 mJy. The median redshift is 0.6, with a range of ∼0.05-4. Only 33% (25 out of 77) of these objects are normal type 1 quasars, with no obscuration. Forty-four percent (34 out of 77) are type 2 objects, with high-ionization, narrow emission lines, and 14% (11 out of 77) are dust-reddened type 1 quasars, showing broad lines but a dust-reddened or unusually weak quasar continuum. Nine percent (7 out of 77) show no sign of an AGN in the optical spectrum, having either starburst spectra or spectra that could be of either starburst or LINER type. These latter objects are analogous to the X-ray-detected population of AGNs with weak or nonexistent optical AGN emission (the X-ray-bright, optically normal galaxies). Of our objects from the SWIRE field, 21 fall within moderately deep XMM-Newton exposures. All the unobscured quasars and about half the obscured quasars are detected in these exposures. This sample, when taken together with other samples of Spitzer-selected AGNs and quasars and results from X-ray studies, confirms that obscured AGNs dominate the AGN and quasar number counts of all rapidly accreting supermassive black hole systems, at least for z ≲ 4. This implies a high radiative efficiency for the black hole accretion process.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/fc28d97c74cbec5373f2e4a324d352a9338c6840

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Citations in the corpus

Evidence for Quasar Activity Triggered by Galaxy Mergers in HST Observations of Dust-reddened Quasars (2007, background): “Lacy et al. (2007) also shows that the type-1 population (unreddened plus lightly reddened) is about 50% of the total quasar population, the remainder being type 2.”
THE SDSS-IV EXTENDED BARYON OSCILLATION SPECTROSCOPIC SURVEY: QUASAR TARGET SELECTION (2015, background): “…mid-infrared (e.g. Lacy et al. 2004; Stern et al. 2005; Richards et al. 2009b; Stern et al. 2012), X-rays (e.g. Trichas et al. 2012), or both (e.g. Lacy et al. 2007; Hickox et al. 2007, 2009); the use of slitless spectroscopy (e.g. Osmer 1982; Schmidt et al. 1986) and the use of variability (e.g.…”
IDENTIFYING LUMINOUS ACTIVE GALACTIC NUCLEI IN DEEP SURVEYS: REVISED IRAC SELECTION CRITERIA (2012, methodology): “As shown in Figure 5, however, these red, power-law dominated AGN occupy a well-defined region of Lacy et al. (2004, 2007) IRAC color space.”
Spectral Energy Distributions of Hard X-Ray Selected Active Galactic Nuclei in the XMM-Newton Medium Deep Survey (2007, unknown): “Optical spectroscopic data are also available from the VVDS for a small subsample (Le Fèvre et al. 2005; Gavignaud et al. 2006), from observations of a selected sample of infrared-selected AGNs (Lacy et al. 2007), and from the 2dF survey (Garcet et al. 2007).”
Revisiting the Unified Model of Active Galactic Nuclei (2015, background): “Reddening of high luminosity high redshift AGNs is also a common phenomenon (e.g. Glikman et al. 2004, Lacy et al. 2007).”
The FIRST-2MASS Red Quasar Survey (2007, background): “Similar distinctions have been made by Lacy et al. (2007) and Brown et al. (2006), who estimate the fraction of reddened type I quasars separately from type II sources.”
Tracing the cosmic growth of supermassive black holes to z ∼ 3 with Herschel (2014, methodology): “The overlapping fraction of AGN obviously increases when considering the wider Lacy et al. (2007) region: we find that 73 per cent of our PEP AGN and 23 per cent of our PEP galaxies are inside the wedge.”
THE SPITZER–WISE SURVEY OF THE ECLIPTIC POLES (2011, background): “Studied in detail by Lacy et al. (2004; 2007) in Figure 21, and Stern et al. (2005) in Figure 22, the red-dashed boxes denote the regions of color–color space that AGNs—both Type-1 and Type-2—tend to occupy.”