The cluster-central compact steep-spectrum radio galaxy 1321+045 (2104.04548v2)

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 30m observations, we investigate the conditions which have triggered this outburst. We find that the previously identified 5 kpc scale radio lobes are probably no longer powered by the AGN, 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 8.48 [+6.04,-3.56] x10^57 erg, only sufficient to balance cooling in the surrounding 16 kpc for ~9 Myr. The cluster ICM properties are similar to those of rapidly cooling nearby clusters, with a low central entropy (8.6 [+2.2,-1.4] kev cm^2 within 8 kpc), short central cooling time (390 [+170,-150] Myr), and t_cool/t_ff and t_cool/t_eddy ratios indicative of thermal instability out to ~45 kpc. Despite previous detection of Halpha emission from the BCG, our IRAM 30m observations do not detect CO emission in either the (1-0) or (3-2) transitions. We place 3sigma limits on the molecular gas mass of M_mol <=7.7x10^9 Msol and <=5.6x10^9 Msol from the two lines respectively. We find indications of a recent minor cluster merger which has left a ~200 kpc tail of stripped gas in the ICM, and probably induced sloshing motions.