2015/03/30 by Youichi Ohyama, Yuichi Terashima, Kazushi Sakamoto · 2 citations
Physics and Astronomy · #Active galactic nucleus #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Infrared #Line (geometry) #Luminous infrared galaxy #Nucleus #Spectral energy distribution #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/805/2/162
27 pages, 11 figures, accepted for publication in ApJ
arxiv created 2015/03/30 · openalex publication_date 2015/05/29 · arxiv updated 2015/06/03 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We investigate signs of an active galactic nucleus (AGN) in the luminous infrared (IR) galaxy NGC 3256 at both IR and X-ray wavelengths. NGC 3256 has double nuclei: the northern and southern (hereafter, N and S nuclei, respectively). We show that the Spitzer IRAC colors extracted at the S nucleus are AGN-like, and the Spitzer IRS spectrum is bluer at μ m than at the N nucleus. We built for the S nucleus an AGN–starburst composite model with a heavily absorbed AGN to successfully reproduce not only the IRAC and IRS specrophotometries at '', but also the very deep silicate 9.7 μ m absorption observed at a 0 36 scale by Díaz-Santos et al. We found a 2.2 μ m compact source at the S nucleus in an HST NICMOS image and identified its unresolved core (at 0 26 resolution) with the compact core in previous mid-infrared observations at comparable resolution. The flux of the 2.2 μ m core is consistent with our AGN spectral energy distribution model. We also analyzed a deeper than ever Chandra X-ray spectrum of the unresolved (at 0 5 resolution) source at the S nucleus. We found that a dual-component power-law model (for primary and scattered ones) fits an apparently very hard spectrum with a moderately large absorption on the primary component. Together with a limit on equivalent width of a fluorescent Fe–K emission line at 6.4 keV, the X-ray spectrum is consistent with a typical Compton-thin Seyfert 2. We therefore suggest that the S nucleus hosts a heavily absorbed low-luminosity AGN.