NuSTAR unveils a heavily obscured low-luminosity Active Galactic Nucleus in the Luminous Infrared Galaxy NGC 6286

Abstract

We report the detection of a heavily obscured Active Galactic Nucleus (AGN) in the luminous infrared galaxy (LIRG) NGC 6286, identified in a 17.5 ks NuSTAR observation. The source is in an early merging stage, and was targeted as part of our ongoing NuSTAR campaign observing local luminous and ultra-luminous infrared galaxies in different merger stages. NGC 6286 is clearly detected above 10 keV and, by including the quasi-simultaneous Swift/XRT and archival XMM-Newton and Chandra data, we find that the source is heavily obscured [$N_{\mathrm{H}}\simeq (0.95-1.32)\times 10^{24}\mathrm{c}{\mathrm{m}}^{-2}$], with a column density consistent with being Compton-thick [CT, $\log (N_{\mathrm{H}}/\mathrm{c}{\mathrm{m}}^{-2})\ge 24$]. The AGN in NGC 6286 has a low absorption-corrected luminosity ($L_{2-10\mathrm{keV}}\sim 3-20\times 10^{41}\mathrm{erg}{\mathrm{s}}^{-1}$) and contributes $\lesssim$1\% to the energetics of the system. Because of its low-luminosity, previous observations carried out in the soft X-ray band ($<10$ keV) and in the infrared did not notice the presence of a buried AGN. NGC 6286 has multi-wavelength characteristics typical of objects with the same infrared luminosity and in the same merger stage, which might imply that there is a significant population of obscured low-luminosity AGN in LIRGs that can only be detected by sensitive hard X-ray observations.

Accepted for publication in ApJ, 14 pages, 7 figures