JCMT mapping of CO(3-2) in the circumnuclear region of M31

Abstract

We present a survey of CO(3-2) molecular line emission in the circumnuclear region of M31 with the James Clerk Maxwell Telescope (JCMT), aiming to explore the physical conditions of the molecular gas. Significant CO(3-2) lines are detected primarily along the so-called nuclear spiral, out to a projected galactocentric radius of 700 pc at a linear resolution of similar to 50 pc. We find that the velocity field of the molecular gas is in rough agreement with that of the ionized gas previously determined from optical observations. Utilizing existed CO(2-1) and CO(1-0) measurements in selected regions of the nuclear spiral, we derive characteristic intensity ratios of CO(3-2)/CO(2-1) and CO(3-2)/CO(1-0), which are both close to unity and are significantly higher than the typical intensity ratios in the disc. Such line ratios suggest high kinetic temperatures of the gas, which might be due to strong interstellar shocks prevalent in the circumnuclear region.