Associated 21-cm HI absorption towards the radio galaxy 3C452 (J2245+3941)

Abstract

We report the detection of 21-cm HI absorption towards the core of the Fanaroff-Riley II radio galaxy 3C452 (J2245+3941). The absorption profile is well resolved into three components; the strongest and narrowest component being coincident with the velocity corresponding to [O III] emission lines while the other two components are blue-shifted with respect to it by ~30 and 115 km\s. If the systemic velocity of the host galaxy is determined from low-ionization lines, which are red-shifted with respect to the [O III] doublet by about ~200 km\s, then both the [O III] emission and 21-cm absorption lines are associated with outflowing material. The neutral hydrogen column density is estimated to be N(HI) = 6.39X10^{20}(T_s/100)(1.0/f_c) cm^{-2}, where T_s and f_c are the spin temperature and partial coverage of the background source respectively. If the 21-cm absorber is also responsible for the nuclear extinction at infrared wavelengths and x-ray absorption, then for a spin temperature of ~8000 K, the absorber occults only ~10 per cent of the radio core.