Mid-Infrared Properties and Color Selection for X-Ray-Detected Active Galactic Nuclei in the MUSYC Extended Chandra Deep Field-South

• Published in: The Astrophysical journal Vol. 680; no. 1; pp. 130 - 142
• Main Authors: Cardamone, Carolin N, Urry, C. Megan, Damen, Maaike, van Dokkum, Pieter, Treister, Ezequiel, Labbé, Ivo, Virani, Shanil N, Lira, Paulina, Gawiser, Eric
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 10-06-2008; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Active galaxies; Quasars; quasars: general; infrared: galaxies; X-ray galaxies; Active galaxy nuclei; X-rays: galaxies; Color; Galaxy nuclei; Cosmic x-ray sources; Infrared galaxies
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/587800

We present the mid-infrared colors of X-ray-detected AGNs and explore mid-infrared selection criteria. Using a statistical matching technique, the likelihood ratio, over 900 IRAC counterparts were identified with a new MUSYC X-ray source catalog that includes [image]1000 published X-ray sources in the Chandra Deep Field-South and Extended Chandra Deep Field-South. Most X-ray- selected AGNs have IRAC spectral shapes consistent with power-law slopes, [image], and display a wide range of colors, [image]. Although X-ray sources typically fit to redder (more negative alpha ) power laws than non-X-ray-detected galaxies, more than 50% do have flat or blue (galaxy-like) spectral shapes in the observed 3-8 [mu]m band. Only a quarter of the X-ray-selected AGNs detected at 24 [mu]m are well fit by featureless red power laws in the observed 3.6-24 [mu]m, likely the subset of our sample whose infrared spectra are dominated by emission from the central AGN region. Most IRAC color selection criteria fail to identify the majority of X-ray-selected AGNs, finding only the more luminous AGNs, the majority of which have broad emission lines. In deep surveys, these color selection criteria select 10%- 20% of the entire galaxy population and miss many moderate-luminosity AGNs.