A New Method for Measuring Metallicities of Young Super Star Clusters

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.

6 pages, 6 figures. Accepted for publication in ApJ

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• Red Supergiants as Cosmic Abundance Probes: massive star clusters in M83, and the mass-metallicity relation of nearby galaxies
• The centres of M83 and the Milky Way: opposite extremes of a common star formation cycle
• The Life Cycle of the Central Molecular Zone. II: Distribution of atomic and molecular gas tracers
• The First Metallicity Study of M83 using the integrated UV light of Star Clusters
• Probing Red Supergiant dynamics through photo-center displacements measured by Gaia
• New infrared spectral indices of luminous cold stars: from early K to M-types
• The Infrared Massive Stellar Content of M83
• Metallicities of Young Massive Clusters in NGC 5236 (M83)
• Chemical abundances of Young Massive Clusters in NGC 1313
• Chemical composition of the young massive cluster NGC 1569-B
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