Galaxy pairs in the Sloan Digital Sky Survey - IX: Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer

摘要

Interactions between galaxies are predicted to cause gas inflows that canpotentially trigger nuclear activity. Since the inflowing material can obscurethe central regions of interacting galaxies, a potential limitation of previousoptical studies is that obscured Active Galactic Nuclei (AGNs) can be missed atvarious stages along the merger sequence. We present the first largemid-infrared study of AGNs in mergers and galaxy pairs, in order to quantifythe incidence of obscured AGNs triggered by interactions. The sample consistsof galaxy pairs and post-mergers drawn from the Sloan Digital Sky Survey thatare matched to detections by the Wide Field Infrared Sky Explorer (WISE). Wefind that the fraction of AGN in the pairs, relative to a mass-, redshift- andenvironment-matched control sample, increases as a function of decreasingprojected separation. This enhancement is most dramatic in the post-mergersample, where we find a factor of 10-20 excess in the AGN fraction comparedwith the control. Although this trend is in qualitative agreement with resultsbased on optical AGN selection, the mid-infrared selected AGN excess increasesmuch more dramatically in the post-mergers than is seen for optical AGN. Ourresults suggest that energetically dominant optically obscured AGNs become moreprevalent in the most advanced mergers, consistent with theoreticalpredictions.