Mathematics – Logic
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21630404g&link_type=abstract
American Astronomical Society, AAS Meeting #216, #304.04; Bulletin of the American Astronomical Society, Vol. 41, p.851
Mathematics
Logic
Scientific paper
We investigate the optical morphologies of candidate active galaxies identified at radio, X-ray, and mid-infrared wavelengths. We use the Advanced Camera for Surveys General Catalog (ACS-GC) to identify 372, 1360, and 1238 AGN host galaxies from the VLA, XMM-Newton and Spitzer Space Telescope observations of the COSMOS field, respectively. We investigate both quantitative (GALFIT) and qualitative (visual) morphologies of these AGN host galaxies, split by brightness in their selection band. We find that the radio-selected AGN are most distinct, with a very low incidence of unresolved optical morphologies, and a high incidence of being hosted by early-type galaxies. In comparison to X-ray selected AGN, mid-IR selected AGN have a slightly higher incidence of being hosted by disk galaxies. These morphological results conform with the results of hic09 who studied the colors and large scale clustering of AGN, and found a general association of radio-selected AGN with the ``red sequence'' galaxies, mid-IR selected AGN with "blue cloud'' galaxies, and X-ray selected AGN straddling these samples in the "green valley.'' We also find that the optical brightness scales with the X-ray and mid-IR brightness, while little correlation is evident between the optical and radio brightnesses. This suggests that the X-ray and mid-IR selected AGN have similar Eddington ratios, while radio-selected AGN represent a different accretion mechanism with a lower and wider range of Eddington ratios. In the general scenario where AGN activity marks and regulates the transition from late-type disk galaxies into massive elliptical galaxies, this work suggests that the earlier stages are most evident as mid-IR selected AGNs. Mid-IR emission is less susceptible to absorption than the relatively soft X-rays probed by XMM-Newton, which are seen at later stages in the transition. Radio-selected AGN are then typically associated with minor bursts of activity in the most massive galaxies.
Griffith Roger
Stern Daniel
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