Dense gas in nearby galaxies XIV . Detection of hot ammonia in Maffei 2

The (J, K) = (1,1), (2,2), (3,3), and (4,4) inversion lines of ammonia (NH3) have been detected toward the nuclear 40′′ sized bar of the nearby spiral galaxy Maffei 2. The relative intensities of the ammonia lines are characterized by a rotational temperature of 85 K. This is higher than rotational temperatures measured toward IC 342 and most Galactic Center clouds, implying kinetic temperatures >∼100 K. Since the kinetic temperature of the gas is larger than that of the dust, NH3 is tracing a particularly dense warm gas component that is heated by young massive stars, cloud-cloud collisions, or ion-slip heating in the nuclear starburst. The gas north of the nucleus (VLSR = –80 km s−1) is more highly excited than the gas further south (+6 km s−1). This asymmetry might be related to pronounced morphological distortions that are observed in the north-eastern part of the galaxy.