Chandra archival study of (U)LIRGs with a double nucleus: binary AGNs?

We present our initial results from a study of 14 (U)LIRGs with a double-nucleus (z < 0.15) and an AGN signature in the Chandra archive. The goals of our study are to search for more possible cases of binary AGNs and to investigate the X-ray properties and energy sources of these energetic objects, a major effort devoted specifically to searching for binary AGNs from (U)LIRGs. Our studies suggest that Mrk 266 might be a new candidate in hosting binary AGNs supported by X-ray observations. Our analysis shows that most (U)LIRGs are essentially weak X-ray sources and are not dominated by AGNs, due to both the lack of Fe K line detections and weak emission in the hard X-ray band. We find evidence for thermal emission with temperature kT similar to 0.7 keV in seven nuclear regions, and this component is possibly associated with the nuclear or circumnuclear starburst. The soft and hard X-ray to far-infrared ratios also suggest that most (U)LIRGs are not energetically dominated by AGNs. Therefore, this study only provides one additional candidate of binary AGNs. We cannot rule out the existence of low luminosity AGNs and thus binary AGNs in all of them, particularly, those highly obscured and spatially unresolved systems. Nine of 14 (U)LIRGs, including three previously known binary AGNs and a new candidate Mrk 266, clearly have obvious X-ray counterparts to their double optical/near-IR nuclei, whereas only two out of 14 have one obvious X-ray counterpart detected. Additionally, Arp 220 and Mrk 273 are not spatially resolved owing to their small nuclear separations (similar to 1 ''), and no significant X-ray detection in the most distant source.