Observations of Ammonia in External Galaxies II. Maffei 2

Abstract The ammonia (J,K) = (1,1), (2,2), (3,3), and (4,4) transitions in the 23.7−24.1 GHz region were searched in a nearby galaxy, Maffei 2, to study the relation between the molecular abundances and the physical conditions in galaxies. The (1,1), (2,2), and (3,3) emission lines were clearly detected. The obtained rotational temperatures and ortho-to-para abundance ratios are about 30 K and about 2.6, respectively. The abundance of NH3 relative to H2 in Maffei 2 was found to be the largest among galaxies where NH3 has already been detected, and the abundance in Maffei 2 is more than an order of magnitude larger than the already reported upper limit in M 82. Hence, we further confirmed the systematically peculiar molecular abundance regarding the formation mechanisms of molecules already reported in M 82.