Whole-disk Sampling of Molecular Clouds in M83

Abstract

We present a catalog of clouds identified from the ^12 CO (1–0) data of M83, which was observed using the Atacama Large Millimeter/submillimeter Array with a spatial resolution of ∼46 pc and a mass sensitivity of ∼10 ^4 M _⊙ (3 σ ). The almost full-disk coverage and high sensitivity of the data allowed us to sample 5724 molecular clouds with a median mass of ∼1.9 × 10 ^5 M _⊙ , which is comparable to the most frequently sampled mass of giant molecular clouds by surveys in the Milky Way (MW). About 60% of the total CO luminosity in M83's disk arises from clouds more massive than 10 ^6 M _⊙ . Such massive clouds comprise 16% of the total clouds in number and tend to concentrate toward the arm, bar, and center, while smaller clouds are more prevalent in interarm regions. Most >10 ^6 M _⊙ clouds have peak brightness temperatures T _peak above 2 K with the current resolution. Comparing the observed cloud properties with the scaling relations determined by P. M. Solomon et al. ( 1987 , hereafter S87 ), T _peak > 2 K clouds follow the relations, but T _peak < 2 K clouds, which are dominant in number, deviate significantly. Without considering the effect of beam dilution, the deviations would suggest modestly high virial parameters (median α _vir ∼ 2.7) and low surface mass densities (median Σ ∼ 22 M _⊙ pc ^−2 ) for the entire cloud samples, which are similar to values found for the MW clouds by T. S. Rice et al. ( 2016 ) and M.-A Miville-Deschênes et al. ( 2017 ). However, once beam dilution is taken into account, the observed α _vir and Σ for a majority of the clouds (mostly T _peak <2 K) can be potentially explained with intrinsic Σ of ∼100 M _⊙ pc ^−2 and α _vir of ∼1, which are similar to the clouds of S87 .

Keywords

• Giant molecular clouds
• Spiral galaxies
• Millimeter astronomy
• CO line emission
• Interstellar medium