NuSTAR Non-detection of a Faint Active Galactic Nucleus in an Ultraluminous Infrared Galaxy with Kpc-scale Fast Wind

Abstract

Large-scale outflows are generally considered to be possible evidence that active galactic nuclei (AGNs) can severely affect their host galaxies. Recently, an ultraluminous infrared galaxy (ULIRG) at z  = 0.49, AKARI J0916248+073034, was found to have a galaxy-scale [O iii] λ 5007 outflow with one of the highest energy-ejection rates at z  < 1.6. However, the central AGN activity estimated from its torus mid-infrared (MIR) radiation is weak relative to the luminous [O iii] emission. In this work we report the first NuSTAR hard X-ray follow-up of this ULIRG to constrain its current AGN luminosity. The intrinsic 2–10 keV luminosity shows a 90% upper limit of 3.0 × 10 43 erg s −1 assuming Compton-thick obscuration ( N H  = 1.5 × 10 24 cm −2 ), which is only 3.6% of the luminosity expected from the extinction-corrected [O iii] luminosity. Using the NuSTAR observation, we successfully identify that this ULIRG has a very extreme case of X-ray deficit among local ULIRGs. A possible scenario to explain the drastic decline in both the corona (X-ray) and torus (MIR) is that the primary radiation from the AGN accretion disk is currently in a fading status, as a consequence of a powerful nuclear wind suggested by powerful ionized outflow in a galaxy scale.