Ultraviolet Spectroscopy of Circumnuclear Star Clusters in M83

TL;DR

This study uses ultraviolet spectroscopy and models to determine the ages and masses of star clusters in M83's starburst region, finding consistent age estimates and evidence of massive star formation.

Contribution

It introduces a comparison of semi-empirical and theoretical UV models for star cluster analysis in a nearby galaxy's starburst region.

Findings

Clusters range from 3 to 20 Myr in age.

Masses of clusters with strong P-Cygni profiles are a few times 10^4 M_sol.

Clusters with P-Cygni profiles contain stars more massive than 30 M_sol.

Abstract

We analyze archival HST/STIS/FUV-MAMA imaging and spectroscopy of 13 compact star clusters within the circumnuclear starburst region of M83, the closest such example. We compare the observed spectra with semi-empirical models, which are based on an empirical library of Galactic O and B stars observed with IUE, and with theoretical models, which are based on a new theoretical UV library of hot massive stars computed with WM-Basic. The models were generated with Starburst99 for metallicities of Z=0.020 and Z=0.040, and for stellar IMFs with upper mass limits of 10, 30, 50, and 100 M_sol. We estimate the ages and masses of the clusters from the best fit model spectra, and find that the ages derived from the semi-empirical and theoretical models agree within a factor of 1.2 on average. A comparison of the spectroscopic age estimates with values derived from HST/WFC3/UVIS multi-band photometry shows a similar level of agreement for all but one cluster. The clusters have a range of ages from about 3 to 20 Myr, and do not appear to have an age gradient along M83's starburst. Clusters with strong P-Cygni profiles have masses of a few times 10^4 M_sol, seem to have formed stars more massive than 30 M_sol, and are consistent with a Kroupa IMF from 0.1-100 M_sol. Field regions in the starburst lack P-Cygni profiles and are dominated by B stars.