Molecular gas in the galaxy M83. II - Kinematics of the molecular gas

TL;DR

This paper analyzes the kinematics of molecular gas in galaxy M83, revealing its rotation, streaming motions, and star formation regions, using CO observations to understand the galaxy's dynamics and gas distribution.

Contribution

It provides detailed kinematic maps and analysis of molecular gas motions, including rotation, streaming, and dispersion, in M83, with new insights into gas dynamics and star formation triggers.

Findings

The galaxy exhibits an inclined, rotating disk with streaming motions along spiral arms.

The dynamical mass of M83 is estimated at about 6x10^10 solar masses.

Star formation correlates with regions where gas density exceeds the critical threshold.

Abstract

We present the kinematics of the molecular gas in the barred spiral galaxy M83 (NGC5236). The study is based on ^{12}CO(J=1--0 and 2--1) observations with the Swedish-ESO Submillimetre Telescope (SEST). Iso-velocity maps of the entire optical disk, 10'x10' or 13x13 kpc, are produced. They show the pattern of an inclined, rotating disk, but also the effects of streaming motions along the spiral arms. A dynamical mass of about 6x10^10 M_sun is estimated by fitting the rotation curve of an exponential disk model to these data. The gas constitutes about 13% of the disk mass. The pattern speed is determined from the residual velocity pattern The locations of various resonances are discussed. The molecular gas velocity dispersion is determined, and a trend of decreasing dispersion with increasing galactocentric radius is found. A total gas (H_2+HI+He) mass surface density map is presented, and compared to the critical density for star formation of an isothermal gaseous disk. The critical density is exceeded in the spiral arms, but not in the interarm regions. The locations of Giant Molecular Associations (GMAs) and HII regions are consistent with this scenario of dynamically induced star formation.