Extended Molecular Gas in the Nearby Starburst Galaxy Maffei 2

Abstract

We present a 9' × 9' fully sampled map of the CO J = 1-0 emission in the nearby starburst galaxy Maffei 2, obtained at the Five College Radio Astronomy Observatory. The map reveals previously known strong CO emission in the central starburst region as well as an extended asymmetric distribution with bright CO lines at the ends of the bar and in a feature at the northeast edge of the molecular disk. This northern feature, proposed previously to be an interacting companion galaxy, could be a dwarf irregular galaxy, although the CO data are also consistent with the feature being simply an extension of one of the spiral arms. We estimate the total molecular gas mass of Maffei 2 to be (1.4-1.7) × 109 M☉ or ~3%-4% of its dynamical mass. Adopting the recently determined lower value for the CO-to-H2 conversion factor in the central region, our data lead to the surprising result that the largest concentrations of molecular gas in Maffei 2 lie at the bar ends and in the putative dwarf companion rather than in the central starburst. A gravitational-stability analysis reveals that the surface density of the extended disk of Maffei 2 lies above the critical density for star formation. However, whether the central region is also gravitationally unstable depends on both the details of the rotation curve and the precise value of the CO-to-H2 conversion factor in this region.