The volume densities of giant molecular clouds in M83

TL;DR

This study measures the volume densities of giant molecular clouds in M83 using FUV fluxes, HI data, and dust estimates, revealing a wide density range and discussing observational biases.

Contribution

It introduces a method combining FUV, HI, and dust data to estimate GMC volume densities in M83, highlighting the density variation within the galaxy.

Findings

GMC surface densities range from 0.1 to 400 cm-3 inside R25.

GMC surface densities range from 0.5 to 50 cm-3 outside R25.

Observational biases may influence the density estimates.

Abstract

Using observed GALEX far-ultraviolet (FUV) fluxes and VLA images of the 21-cm HI column densities, along with estimates of the local dust abundances, we measure the volume densities of a sample of actively star-forming giant molecular clouds (GMCs) in the nearby spiral galaxy M83 on a typical resolution scale of 170 pc. Our approach is based on an equilibrium model for the cycle of molecular hydrogen formation on dust grains and photodissociation under the influence of the FUV radiation on the cloud surfaces of GMCs. We find a range of total volume densities on the surface of GMCs in M83, namely 0.1 - 400 cm-3 inside R25, 0.5 - 50 cm-3 outside R25 . Our data include a number of GMCs in the HI ring surrounding this galaxy. Finally, we discuss the effects of observational selection, which may bias our results.