Molecular Gas in Classical Elliptical Radio Galaxies

Abstract

We report the results of two comprehensive surveys for CO molecular gas in classical (i.e., extended double-lobed) radio galaxies, all of which are classified as elliptical (or perhaps SO) galaxies. Our first survey comprises all twenty-four elliptical galaxies in the revised 3C catalog at redshifts z less than or equal to 0.031; only one, 3C 84 (Perseus A), had previously been detected in molecular gas, with a mass of similar to1010 M-circle dot. We detected four galaxies in this sample for the first time. Our second survey comprises all twenty-one classical elliptical (or SO) radio galaxies in the northern hemisphere at z less than or equal to 0.023 exceeding a selected radio flux density, including seven of the 3C galaxies (four detected) in our first survey. We detected another four galaxies in this sample for the first time. Six of the eight galaxies detected have molecular gas masses in the narrow range 2-4 x 10(8) M-circle dot, which is comparable to that in Centaurus A, and in all span the range 1 x 10(7)-1 x 10(9) M-circle dot. All have very broad double-homed line profiles characteristic of a central rotating disk or torus. The remaining galaxies have upper limits in molecular gas mass of a few 10(8) M-circle dot, and in one case a few 10(7) M-circle dot. By contrast, previous surveys of radio galaxies had found molecular gas masses of 10(9)-10(10) M-circle dot, but these surveys preferentially selected IR-bright (i.e., dusty) galaxies, and many of the detections are of systems with compact (nuclear) radio emission hosted by disk or merging galaxies. Our results suggest that the molecular gas in most classical elliptical radio galaxies probably originate from the cannibalism of a relatively low-mass but gas-rich galaxy by the dominant host elliptical galaxy, as proposed by Lim et al. (2000) based on early results from the first survey.