The First Metallicity Study of M83 Using the Integrated UV Light of Star Clusters *

Abstract

Stellar populations are powerful tools for investigating the evolution of extragalactic environments. We present the first UV integrated-light spectroscopic observations for 15 young star clusters in the starburst M83 with a special focus on metallicity measurements. The data were obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope . We analyze the data by applying an abundance technique that has previously been used to study an optical set of star clusters. We estimate a central metallicity of [ Z ] = +0.20 ± 0.15 dex, in agreement with estimates obtained through independent methods, i.e., J band and blue supergiants. We estimate a UV metallicity gradient of −0.041 ± 0.022 dex kpc −1 , which is consistent with the optical metallicity gradient of −0.040 ± 0.032 dex kpc −1 for . Combining our stellar metallicities, UV and optical, with those from H ii regions (strong-line abundances based on empirical calibrations), we identify two possible breaks in the gradient of M83 at galactocentric distances of R  ∼ 0.5 and 1.0 R 25 . If the abundance breaks are genuine, the metallicity gradient of this galaxy follows a steep-shallow-steep trend, a scenario predicted by three-dimensional numerical simulations of disk galaxies. The first break is located near the corotation radius. This first steep gradient may have originated in recent star formation episodes and a relatively young bar (<1 Gyr). In the numerical simulations, the shallow gradient is created by the effects of dilution by outflow, where low-metallicity material is mixed with enriched gas. Finally, the second break and last steep gradient mark the farthest galactocentric distances where the outward flow has penetrated.