Cavities, shocks and a cold front around 3C 320

Abstract

Abstract We present results obtained from the analysis of a total of 110 ks of Chandra observations of the Fanaroff–Riley class II (FR II) radio galaxy 3C 320, located at the centre of a cluster of galaxies at redshift z = 0.342. A pair of X-ray cavities has been detected at an average distance of ∼38 kpc along the east and west directions, with cavity energy, age and total power equal to ∼7.7 × 1059 erg, ∼7 × 107 yr and ∼3.5 × 1044 erg s−1, respectively. The cooling luminosity within the cooling radius of ∼100 kpc was found to be Lcool ∼ 8.5 × 1043 erg s−1. Comparison of these two estimates (total cavity power and cooling luminosity) implies that the cavity power is sufficiently high to balance radiative loss. A pair of weak shocks has also been detected at distances of ∼47 and ∼76 kpc surrounding the radio bubbles. Using the observed density jumps of ∼1.8 and ∼2.1 at the shock locations along the east and west directions, we estimate the Mach numbers ($\mathcal {M}$) to be ∼1.6 and ∼1.8, respectively. A sharp surface-brightness edge was also detected at a relatively larger radius (∼80 kpc) along the south direction. The density jump at this surface-brightness edge was estimated to be ∼1.6 and it is probably due to the presence of a cold front in this cluster. The far-infrared luminosity yielded a star formation rate of 51 M⊙ yr−1, which is a quarter of the cooling rate ($\dot{M}$ ∼ 192 M⊙ yr−1).