A Chandra-Swift view of point sources in Hickson compact groups : high agn fraction but a dearth of strong AGNs

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DOIResolve DOI: http://doi.org/10.1088/0067-0049/212/1/9
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TypeArticle
Journal titleAstrophysical Journal, Supplement Series
ISSN0067-0049
Volume212
Issue1
Article number9
Subjectcatalogs; galaxies: active; galaxies: nuclei; ultraviolet: galaxies; X-rays: galaxies
AbstractWe present Chandra X-ray point source catalogs for 9 Hickson Compact Groups (HCGs, 37 galaxies) at distances of 34-89 Mpc. We perform detailed X-ray point source detection and photometry and interpret the point source population by means of simulated hardness ratios. We thus estimate X-ray luminosities (Lx ) for all sources, most of which are too weak for reliable spectral fitting. For all sources, we provide catalogs with counts, count rates, power-law indices (Γ), hardness ratios, and Lx , in the full (0.5-8.0 keV), soft (0.5-2.0 keV), and hard (2.0-8.0 keV) bands. We use optical emission-line ratios from the literature to re-classify 24 galaxies as star-forming, accreting onto a supermassive black hole (AGNs), transition objects, or low-ionization nuclear emission regions. Two-thirds of our galaxies have nuclear X-ray sources with Swift/UVOT counterparts. Two nuclei have L x, 0.5-8.0 keV >10^42 erg s-1, are strong multi-wavelength active galactic nuclei (AGNs), and follow the known αOX-νL ν (nearUV) correlation for strong AGNs. Otherwise, most nuclei are X-ray faint, consistent with either a low-luminosity AGN or a nuclear X-ray binary population, and fall in the "non-AGN locus" in αOX-νL ν (nearUV) space, which also hosts other normal galaxies. Our results suggest that HCG X-ray nuclei in high specific star formation rate spiral galaxies are likely dominated by star formation, while those with low specific star formation rates in earlier types likely harbor a weak AGN. The AGN fraction in HCG galaxies with MR ≤ -20 and L x, 0.5-8.0 keV ≥10^41 erg s-1 is 0.08 +0.035/-0.01, somewhat higher than the 5% fraction in galaxy clusters.
Publication date
LanguageEnglish
AffiliationNational Science Infrastructure; National Research Council Canada
Peer reviewedYes
NPARC number21274128
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Record identifiere4ac7fb9-a702-40f1-b11e-77ba4cd126ab
Record created2015-02-17
Record modified2016-05-09
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