The Hot Gas Environment of the Radio Galaxy 3C 388: Quenching the Accumulation of Cool Gas in a Cluster Core by a Nuclear Outburst

We present results from a 35 ks {\em Chandra}/ACIS-I observation of the hotICM around the FR II radio galaxy 3C 388. 3C 388 resides in a clusterenvironment with an ICM temperature of $\sim$3.5 keV. We detect cavities in theICM coincident with the radio lobes. The enthalpy of these cavities is$\sim1.2\times10^{60}$ ergs. The work done on the gas by the inflation of thelobes is $\sim3\times10^{59}$ ergs, or $\sim$0.87 keV per particle out to theradius of the lobes. The radiative timescale for gas at the center of thecluster at the current temperature is a few Gyrs. The gas in the core wasprobably cooler and denser before the outburst, so the cooling time wasconsiderably shorter. We are therefore likely to be witnessing the quenching ofa cluster cooling flow by a radio galaxy outburst. The mechanical power of thelobes is at least 20 times larger than the radiative losses out to the coolingradius. Outbursts of similar power with a $\sim$5% duty cycle would be morethan sufficient to continually reheat the cluster core over the Hubble time andprevent the cooling of any significant amount of gas. The mechanical power ofthe outburst is also roughly two orders of magnitude larger than either theX-ray luminosity of the active nucleus or the radio luminosity of the lobes.The equipartition pressure of the radio lobes is more than an order ofmagnitude lower than that of the ambient medium, indicating that the pressureof the lobe is dominated by something other than the relativistic electronsradiating at GHz frequencies.Comment: 28 pages, 10 figures - accepted for publication in the Astrophysical Journa