PRIMUS: Infrared and X-Ray agn selection techniques at 0.2 < z < 1.2

Alexander J. Mendez, Alison L. Coil, James Aird, Aleksandar M. Diamond-Stanic, John Moustakas, Michael R. Blanton, Richard J. Cool, Daniel J. Eisenstein, Kenneth C. Wong, Guangtun Zhu

    Research output: Contribution to journalArticlepeer-review


    We present a study of Spitzer/IRAC and X-ray active galactic nucleus (AGN) selection techniques in order to quantify the overlap, uniqueness, contamination, and completeness of each. We investigate how the overlap and possible contamination of the samples depend on the depth of both the IR and X-ray data. We use Spitzer/IRAC imaging, Chandra and XMM-Newton X-ray imaging, and spectroscopic redshifts from the PRism MUlti-object Survey to construct galaxy and AGN samples at 0.2 < z < 1.2 over 8 deg2. We construct samples over a wide range of IRAC flux limits (SWIRE to GOODS depth) and X-ray flux limits (10 ks to 2 Ms). We compare IR-AGN samples defined using both the IRAC color selection of Stern et al. and Donley et al. with X-ray-detected AGN samples. For roughly similar depth IR and X-ray surveys, we find that 75% of IR-selected AGNs are also identified as X-ray AGNs. This fraction increases to 90% when comparing against the deepest X-ray data, indicating that at most 10% of IR-selected AGNs may be heavily obscured. The IR-AGN selection proposed by Stern et al. suffers from contamination by star-forming galaxies at various redshifts when using deeper IR data, though the selection technique works well for shallow IR data. While similar overall, the IR-AGN samples preferentially contain more luminous AGNs, while the X-ray AGN samples identify a wider range of AGN accretion rates including low specific accretion rate AGNs, where the host galaxy light dominates at IR wavelengths. The host galaxy populations of the IR and X-ray AGN samples have similar rest-frame colors and stellar masses; both selections identify AGNs in blue, star-forming and red, quiescent galaxies.

    Original languageEnglish (US)
    Article number40
    JournalAstrophysical Journal
    Issue number1
    StatePublished - Jun 10 2013


    • X-rays: galaxies
    • galaxies: active
    • galaxies: evolution
    • infrared: galaxies

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


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