Are the High Molecular Mass Fractions in Nearby Spiral Nuclei Real?

Summary

ABSTRACT

We examine the question of whether the molecular mass fractions of > 50% in the inner 100–200 pc of nearby starburst galaxies are real. If so, this result would imply that molecular gas has a significant impact on the dynamics of the nuclear regions of these galaxies.

INTRODUCTION

It has been known for some time that the centers of spiral galaxies are often rich repositories of molecular gas (Young and Scoville 1991), often much richer than the spiral disks. Molecular gas masses are sufficient to fuel the vigorous star formation seen in galactic nuclei, even in “starbursts”. Recent interferometric maps have revealed that nuclear gas is distributed in coherent, nonaxisymmetric structures which are often described as “bar-like”, structures which are generally seen reflected in the starburst as well.

An example of a gas-rich nucleus with a high star formation (SF) rate is the center of the nearby spiral galaxy, IC 342. IC 342 has a barlike CO distribution in the nucleus (Lo et al. 1984), which at high resolution resolves into two very open arms of gas that continue to within 50 pc of the nucleus (Ishizuki et al. 1990; Turner and Hurt 1992). There are also spiral arms observed in Hα (J. S. Young, private communication).