Red Supergiants as Cosmic Abundance Probes: massive star clusters in M83, and the mass-metallicity relation of nearby galaxies

TL;DR

This study uses Red Supergiants in star clusters of M83 to measure metallicity, revealing a flat abundance gradient and constructing a mass-metallicity relation consistent with other stellar and nebular methods.

Contribution

It demonstrates that integrated light from Red Supergiants can reliably determine galaxy metallicities, providing a new stellar-based approach for abundance analysis.

Findings

Inner region metallicity gradient in M83 is flat.

Red Supergiants-based metallicities agree with hot star analyses.

Constructed a mass-metallicity relation consistent with other methods.

Abstract

We present an abundance analysis of seven super-star clusters in the disk of M83. The near-infrared spectra of these clusters are dominated by Red Supergiants, and the spectral similarity in the J-band of such stars at uniform metallicity means that the integrated light from the clusters may be analysed using the same tools as those applied to single stars. Using data from VLT/KMOS we estimate metallicities for each cluster in the sample. We find that the abundance gradient in the inner regions of M83 is flat, with a central metallicity of [Z] = 0.21$\pm$0.11 relative to a Solar value of $Z_\odot$=0.014, which is in excellent agreement with the results from an analysis of luminous hot stars in the same regions. Compiling this latest study with our other recent work, we construct a mass-metallicity relation for nearby galaxies based entirely on the analysis of RSGs. We find excellent agreement with the other stellar-based technique, that of blue supergiants, as well as with temperature-sensitive (`auroral' or `direct') \hii-region studies. Of all the HII-region strong-line calibrations, those which are empirically calibrated to direct-method studies (N2 and O3N2) provide the most consistent results.