Obscured and Unobscured Active Galactic Nuclei in the Spitzer Space Telescope First Look Survey

By M. Lacy, L. Storrie-Lombardi, A. Sajina, P. Appleton, Lee Armus, S. Chapman, P. Choi, D. Fadda, F. Fang, D. Frayer and 12 more. 2004

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Selection of active galactic nuclei (AGNs) in the infrared facilitates the discovery of AGNs whose optical emission is extinguished by dust. In this paper, we use the Spitzer Space Telescope First Look Survey (FLS) to assess the fraction of AGNs with mid-infrared (MIR) luminosities that are comparable to quasars and that are missed in optical quasar surveys because of dust obscuration. We begin by using the Sloan Digital Sky Survey (SDSS) database to identify 54 quasars within the 4 deg2 extragalactic FLS. These quasars occupy a distinct region in MIR color space by virtue of their strong, red continua. This has allowed us to define an MIR color criterion for selecting AGN candidates. About 2000 FLS objects have colors that are consistent with them being AGNs, but most are much fainter in the MIR than the SDSS quasars, which typically have 8 μm flux densities S8.0 ∼ 1 mJy. We have investigated the properties of 43 objects with S8.0 ≥ 1 mJy that satisfy our AGN color selection. This sample should contain both unobscured quasars as well as AGNs that are absent from the SDSS survey because of extinction in the optical. After removing 16 known quasars, three probable normal quasars, and eight spurious or confused objects from the initial sample of 43, we are left with 16 objects that are likely to be obscured quasars or luminous Seyfert 2 galaxies. This suggests that the numbers of obscured and unobscured AGNs are similar in samples selected in the MIR at S8.0 ∼ 1 mJy.

Subfields: Astronomy and Astrophysics, Instrumentation

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THE SDSS-III BARYON OSCILLATION SPECTROSCOPIC SURVEY: THE QUASAR LUMINOSITY FUNCTION FROM DATA RELEASE NINE (2012, background): “We leave investigations of the obscured AGN population to other studies, e.g., in the mid-infrared (e.g., Lacy et al. 2004; Richards et al. 2006a; Stern et al. 2012; Yan et al. 2012), and X-ray (Tueller et al. 2010; Luo et al. 2011; Corral et al. 2011; Brightman & Ueda 2012; Lehmer et al. 2012).”
MID-INFRARED SELECTION OF ACTIVE GALACTIC NUCLEI WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER. II. PROPERTIES OF WISE-SELECTED ACTIVE GALACTIC NUCLEI IN THE NDWFS BOÖTES FIELD (2012, methodology): “For comparison, we also show the numbers for the IRAC-based selection criteria of Lacy et al. (2004, 2007), Stern et al. (2005) and Messias et al. (2012), calculated using the SDWFS photometry.”
Cosmic X-ray surveys of distant active galaxies (2015, methodology): “Color-color selection from MIR photometric data (e.g., Lacy et al 2004; Stern et al 2005; Polletta et al 2006; Hickox et al 2007; Cardamone et al 2008; Donley et al 2008, 2012; Mateos et al 2013).”
Evidence for Quasar Activity Triggered by Galaxy Mergers in HST Observations of Dust-reddened Quasars (2007, background): “Optical quasar surveys tend to miss dust-reddened quasars which have been found either with infrared surveys (Cutri et al. 2001; Lacy et al. 2004), radio surveys (White et al. 2003), hard X-ray surveys (Norman et al. 2002), or surveys for high-ionization narrow-line objects (Zakamska et al. 2006).”
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 (2006, methodology): “Spitzer data has been used to find highly-obscured AGN, both through midinfrared color selection (Lacy et al. 2004 [hereafter Paper I], 2005a; Stern et al. 2005; Alonso-Herrero et al. 2005; Polletta et al. 2006) and joint radioinfrared selection (Mart́ınez-Sansigre et al. 2005, 2006; Weedman et al.…”
A Highly Complete Spectroscopic Survey of the GOODS-N Field (2008, background): “We mark with green dashed lines the region considered to contain AGNs by Lacy et al. (2004).”
The dusty heart of nearby active galaxies. II. From clumpy torus models to physical properties of dust around active galactic nuclei (2009, background): “…from direct observations of the pc-scaled molecular gas in nearby AGN, it is inferred that the torus is not only optically thick but also geometrically thick, with a characteristic scale heighth/r ∼ 1 (e.g. Maiolino & Rieke 1995; Lacy et al. 2004; Martı́nez-Sansigre et al. 2006; Hicks et al. 2009).”
Multiwavelength Study of Massive Galaxies at z ~ 2. II. Widespread Compton-thick Active Galactic Nuclei and the Concurrent Growth of Black Holes and Bulges (2007, background): “For example, selection by means of red IRAC (3.5–8µm) colors were presented by Lacy et al. (2004), Stern et al. (2005), and similarly the selection by means of power-law spectral energy distributions (SEDs) over IRAC bands (Alonso Herrero et al. 2006; Donley et al. 2007) have provided AGN candidate…”
Galaxy Interactions Trigger Rapid Black Hole Growth: an unprecedented view from the Hyper Suprime-Cam Survey (2017, methodology): “…color-color diagrams developed using 2, 3 or 4-band mid-IR photometry taken using the IRAC instrument on the NASA Spitzer Space Telescope (e.g., Lacy et al. 2004; Stern et al. 2005; AlonsoHerrero et al. 2006; Donley et al. 2012, or more recently using WISE (e.g., Jarrett et al. 2011; Stern et…”
DETERMINING STAR FORMATION RATES FOR INFRARED GALAXIES (2008, unknown): “Behavior of IRAC Colors Lacy et al. (2004) and Stern et al. (2005) proposed two forms of IRAC color-color diagram to separate star forming galaxies from those with substantial AGN contributions to their mid-infrared emission.”
Quasar feedback and the origin of radio emission in radio-quiet quasars (2014, background): “The mid-infrared colors and fluxes of type 2 quasars at these luminosities are dominated by the quasar, not by the host galaxy (Lacy et al. 2004; Stern et al. 2005; Zakamska et al. 2008).”
Spitzer Quasar and ULIRG Evolution Study (QUEST). II. The Spectral Energy Distributions of Palomar-Green Quasars (2007, methodology): “For example, Lacy et al. (2004) found that detection methods based on MIR colors are efficient tools for selecting all types of AGNs (and also starburst galaxies).”
Photometric redshifts in the SWIRE Survey (2008, background): “This condition is a good selector of objects with strong AGN dust tori (Lacy et al 2004).”
IDENTIFICATION OF 1.4 MILLION ACTIVE GALACTIC NUCLEI IN THE MID-INFRARED USING WISE DATA (2015, methodology): “In choosing a mid-IR color selection criteria, we required that the criteria be defined directly from WISE data, using only WISE data; this rules out the criteria of Lacy et al. (2004), Stern et al. (2005), Lacy et al. (2007), and Donley et al. (2012), which apply to Spitzer IRAC data.”
QUANTIFYING QUASAR VARIABILITY AS PART OF A GENERAL APPROACH TO CLASSIFYING CONTINUOUSLY VARYING SOURCES (2009, methodology): “Recently, Kozłowski & Kochanek (2009) used mid-IR color selection (e.g., Stern et al. 2005; also see Lacy et al. 2004) to identify a large sample of quasar candidates in the Magellanic Clouds.”
THE SDSS-IV EXTENDED BARYON OSCILLATION SPECTROSCOPIC SURVEY: QUASAR TARGET SELECTION (2015, unknown): “…et al. 2012), or both (e.g. Glikman et al. 2012); the lack of an observed proper motion (e.g. Kron & Chiu 1981), the use of the 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;…”
The FIRST-2MASS Red Quasar Survey (2007, methodology): “Ongoing quasar surveys using the Spitzer Space Telescope should avoid this problem and yield quasar samples unbiased by extinction (e.g., Lacy et al. 2004; Stern et al. 2005).”
The Infrared Luminosity Function of Galaxies at Redshifts z = 1 and z ~ 2 in the GOODS Fields (2007, methodology): “Similar colour-colour plots have been used with the purpose of separating normal and active galaxies elsewhere (e.g. Lacy et al. 2004; Stern et al. 2005; Caputi et al. 2006b).”
Spitzer Observations of Massive, Red Galaxies at High Redshift (2005, background): “Alternatively galaxies dominated by AGN emission in the rest-frame near-IR should have redder IRAC colors (see, e.g., Rieke 1978; Neugebauer et al. 1979; Lacy et al. 2004; Alonso-Herrero et al. 2006; Stern et al. 2005).”
Spectral Energy Distributions of Hard X-Ray Selected Active Galactic Nuclei in the XMM-Newton Medium Deep Survey (2007, unknown): “Only 5 of 87 sources in sample Awith detections in all four IRAC bands are not within the ‘‘AGN wedge’’ as defined by Lacy et al. (2004).”