Molecular Gas Properties in M83 from CO PDFs

TL;DR

This study analyzes molecular gas properties in M83 using high-resolution CO observations, revealing structural differences in gas distribution and dynamics between the galaxy's bar and arm regions, and assessing the impact of stellar feedback.

Contribution

It provides the first detailed comparison of CO PDFs in different galactic structures of M83, highlighting how bar dynamics influence gas properties and star formation.

Findings

I_CO PDF shows a bright-end tail in the bar but not in the arm.

Velocity dispersion is larger in the bar than in the arm.

Stellar feedback does not explain the differences in I_CO PDFs.

Abstract

We have obtained 12CO(1--0) data of the nearby barred spiral galaxy M83 from Atacama Large Millimeter/submillimeter Array and Nobeyama 45m observations. By combining these two data sets, the total CO flux has been recovered, and a high angular resolution (2" corresponding to ~40 pc at the distance of M83) has been achieved. The field of view is 3' corresponding to ~3.4 kpc and covers the galactic center, bar, and spiral arm regions. In order to investigate how these galactic structures affect gas properties, we have created a probability distribution function (PDF) of the CO integrated intensity (I_CO), peak temperature, and velocity dispersion for a region with each structure. We find that the I_CO PDF for the bar shows a bright-end tail while that for the arm does not. Since the star formation efficiency is lower in the bar, this difference in PDF shape is contrary to the trend in Milky Way studies where the bright-end tail is found for star-forming molecular clouds. While the peak temperature PDFs are similar for bar and arm regions, velocity dispersion in bar is systematically larger than in arm. This large velocity dispersion is likely a major cause of the bright-end tail and of suppressed star formation. We also investigate an effect of stellar feedback to PDF profiles and find that the different I_CO PDFs between bar and arm regions cannot be explained by the feedback effect, at least at the current spatial scale.