The Cluster-central Compact Steep-spectrum Radio Galaxy 1321+045

Abstract

Abstract The radio galaxy 1321+045 is a rare example of a young, compact steep-spectrum source located in the center of a z = 0.263 galaxy cluster. Using a combination of Chandra, VLBA, VLA, MERLIN, and IRAM 30 m observations, we investigate the conditions that have triggered this outburst. We find that the previously identified 5 kpc scale radio lobes are probably no longer powered by the active galactic nucleus, which seems to have launched a new ∼20 pc jet on a different axis, likely within the last few hundred years. We estimate the enthalpy of the lobes to be , only sufficient to balance cooling in the surrounding 16 kpc for ∼9 Myr. The properties of the cluster’s intracluster medium (ICM) are similar to those of rapidly cooling nearby clusters, with a low central entropy (8.6 keV cm2 within 8 kpc), short central cooling time (390 Myr), and t cool/t ff and t cool/t eddy ratios indicative of thermal instability out to ∼45 kpc. Despite previous detection of Hα emission from the brightest cluster galaxy, our IRAM 30 m observations do not detect CO emission in either the (1–0) or (3–2) transitions. We place 3σ limits on the molecular gas mass of M mol ≤ 7.7 × 109 M ⊙ and ≤5.6 × 109 M ⊙ from the two lines respectively. We find indications of a recent minor cluster merger that has left a ∼200 kpc tail of stripped gas in the ICM, and probably induced sloshing motions.