2007MNRAS.374.1185C

We investigate the atomic and molecular interstellar medium and star formation of NGC275, the late-type spiral galaxy in Arp140, which is interacting with NGC274, an early-type system. The atomic gas (Hi) observations reveal a tidal tail from NGC275 which extends many optical radii beyond the interacting pair. The Hi morphology implies a prograde encounter between the galaxy pair approximately ∼1.5x10⁸yr ago. The Hα emission from NGC275 indicates clumpy irregular star formation, clumpiness which is mirrored by the underlying mass distribution as traced by the K_s-band emission. The molecular gas distribution is striking in its anticorrelation with the Hii regions. Despite the evolved nature of NGC275's interaction and its barred potential, neither the molecular gas nor the star formation is centrally concentrated. We suggest that this structure results from stochastic star formation leading to preferential consumption of the gas in certain regions of the galaxy. In contrast to the often-assumed picture of interacting galaxies, NGC275, which appears to be close to merger, does not display enhanced or centrally concentrated star formation. If the eventual merger is to lead to a significant burst of star formation it must be preceded by a significant conversion of atomic to molecular gas as at the current rate of star formation all the molecular gas will be exhausted by the time the merger is complete.