Mathematics – Logic
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21714906t&link_type=abstract
American Astronomical Society, AAS Meeting #217, #149.06; Bulletin of the American Astronomical Society, Vol. 43, 2011
Mathematics
Logic
Scientific paper
We conduct a mid-infrared census of nine galaxy clusters with a total of 1517 spectroscopically confirmed member galaxies. Mid-IR color selection techniques were applied to identify active galactic nuclei (AGN) using Spitzer IRAC photometry. We find 12 candidate IR-AGN from a total of 712 cluster galaxies that have ≥3σ detections in all IRAC channels. To compare AGN activity across our redshift range we select three types of complete samples of galaxies: (1) galaxies with rest-frame [3.6]μm luminosity >1.3 × 1044 erg s-1, (2) a sample of the 100 brightest [3.6]μm galaxies and (3) galaxies with absolute VAB magnitude <-21.5. For all three samples we observe a tendency for the fraction of IR-AGN in cluster galaxies (fAGN) to increase with redshift. We observe the most rapid change between z ≈ 1.2 and 0.8 where fAGN drops from 15±8% to 3±2%, a time-span of 1.5 Gyr. In general we find fAGN ≈ 1±1% at z < 0.7 but at z > 0.7 we calculate fAGN≈ 5±2%. The mid infrared AGN fraction for field galaxies in the Spitzer Extragalactic First Look Survey(XFLS) is 7±1% at z < 0.7 for galaxies with [3.6]μm ≥ 100 μJy. In agreement with recent studies, we find that IR-AGN are predominantly hosted by late-type galaxies that preferentially occupy the blue-cloud. We further observe that the most luminous IR-AGN from our sample (a) are accompanied by X-ray emission, (b) are located ≥0.5 Mpc from the cluster center and (c) appear highly morphologically disturbed. These results support a scenario where X-ray-luminous AGN likely result from interactions/mergers of galaxies during infall into the cluster potential, simultaneously boosting the mid-IR signature.
Saintonge Amelie
Tomczak Adam
Vy-Tran K.
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