A New Method for Measuring Metallicities of Young Super Star Clusters

TL;DR

This paper introduces a spectroscopic method in the J-band to accurately measure the metallicities of young super star clusters, enabling studies of galaxy composition at various distances.

Contribution

The paper presents a novel spectroscopic technique utilizing near-infrared flux dominated by red supergiants for metallicity measurement in super star clusters.

Findings

Measured metallicity of M83 super star clusters as [Z]= +0.28 +/- 0.14 dex.

Determined metallicity of NGC 6946 super star clusters as [Z]= -0.32 +/- 0.20 dex.

Method enables metallicity measurements across galaxy disks up to 70 Mpc.

Abstract

We demonstrate how the metallicities of young super star clusters can be measured using novel spectroscopic techniques in the J-band. The near-infrared flux of super star clusters older than ~6 Myr is dominated by tens to hundreds of red supergiant stars. Our technique is designed to harness the integrated light of that population and produces accurate metallicities for new observations in galaxies above (M83) and below (NGC 6946) solar metallicity. In M83 we find [Z]= +0.28 +/- 0.14 dex using a moderate resolution (R~3500) J-band spectrum and in NGC 6496 we report [Z]= -0.32 +/- 0.20 dex from a low resolution spectrum of R~1800. Recently commissioned low resolution multiplexed spectrographs on the VLT (KMOS) and Keck (MOSFIRE) will allow accurate measurements of super star cluster metallicities across the disks of star-forming galaxies up to distances of 70 Mpc with single night observation campaigns using the method presented in this letter.