The Effect of a Chandra -measured Merger-related Gas Component on the Lobes of a Dead Radio Galaxy

We use Chandra data to infer that an X-ray bright component of gas is in theprocess of separating the radio lobes of 3C 442A. This is the first radiogalaxy with convincing evidence that central gas, overpressured with respect tothe lobe plasma and not simply a static atmosphere, is having a major dynamicaleffect on the radio structure. We speculate that the expansion of the gas alsore-excites electrons in the lobes of 3C 442A through compression and adiabaticheating. Two features of 3C 442A contribute to its dynamical state. Firstly,the radio source is no longer being powered by a detected active jet, so thatthe dynamical state of the radio plasma is at the mercy of the ambient medium.Secondly the two early-type galaxies, NGC 7236 and NGC 7237, one of which wasthe original host of 3C 442A, are undergoing a merger and have alreadyexperienced a close encounter, suggesting that the X-ray bright gas is mostlythe heated combined galaxy atmospheres. The lobes have been swept apart forabout 10^8 yrs by the pressure-driven expansion of the X-ray bright inner gas.Comment: 4 pages, 4 figures. Accepted for publication in ApJ Letter