The location of an active nucleus and a shadow of a tidal tail in the ULIRG Mrk 273

Abstract

Analysis of data from the Chandra X-ray Observatory for the double nucleus ULIRG Mrk 273 reveals an absorbed hard X-ray source coincident with the southwest nucleus, implying that this unresolved near infrared source is where an active nucleus resides while the northern nuclear region contains a powerful starburst which dominates the far infrared luminosity. There is evidence of a slight image extension in the 6-7 keV band, where a Fe K line is present, towards the northern nucleus. A large-scale, diffuse emission nebula detected in soft X-rays contains a dark lane that spatially coincides with a high surface-brightness tidal tail extending ~50 arcsec (40 kpc) to the south. The soft X-ray source is likely located behind the tidal tail which absorbs X-ray photons along the line of sight. The estimated column density of cold gas in the tidal tail responsible for shadowing the soft X-rays is nH >= 6e+21 cm-2, consistent with the tidal tail having an edge-on orientation.