HI Absorption in Radio Ellipticals: More Evidence for Infall
A complete sample of 29 radio galaxies with compact cores has been observed with the VLA in the HI line to an almost uniform optical depth sensitivity of τ = 0.01 at a velocity resolution of 40 km s-1. HI absorption was detected in four galaxies, NGC 3894, NGC 5363, 3C236 and 4C31.04, bringing to eight the number of radio ellipticals in which HI absorption has been detected. In all cases, absorption is seen redshifted with respect to the galaxy’s systemic velocity, or close to the systemic velocity or both. No blueshifted absorption components are seen. These observations demonstrate the infall of HI to the inner regions of radio elliptical galaxies. The estimated infall rates (a few hundredth of a solar mass per year) are more than adequate to fuel the nuclear activity.
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