CLusters in the Uv as EngineS (CLUES): I. Survey presentation \& FUV spectral analysis of the stellar light

TL;DR

The CLUES survey uses HST FUV spectroscopy and photometry to analyze young, massive star clusters, revealing their ages, metallicities, and extinctions, and improving understanding of stellar populations in galaxies.

Contribution

This paper presents the first detailed analysis of 20 young star clusters using combined FUV spectroscopy and photometry, highlighting the advantages of spectroscopy in constraining stellar properties.

Findings

FUV spectroscopy better constrains stellar metallicities.

Photometric and spectroscopic ages agree for clusters younger than 5 Myr.

Mass estimates are consistent within a factor of 2.

Abstract

The CLusters in the Uv as EngineS (CLUES) survey is a Cosmic Origins Spectrograph (COS) campaign aimed at acquiring the 1130 to 1770 {\AA}, restframe spectroscopy of very young (<20 Myr) and massive (>10^4 solar masses) star clusters in galaxies that are part of the Hubble treasury program Legacy ExtraGalactic Uv Survey (LEGUS). In this first paper of a series, we describe the CLUES sample consisting of 20 young star clusters and report their physical properties as derived by both multi-wavelength photometry and far-UV (FUV) spectroscopy with Hubble Space Telescope (HST). Thanks to the synergy of the two different datasets we build a coherent picture of the diverse stellar populations found in each region (with sizes of 40 to 160 pc). We associate the FUV-brightest stellar population to the central targeted star cluster and the other modeled population to the diffuse stars that are included in the COS aperture. We observe better agreement between photometric and spectroscopic ages for star clusters younger than 5 Myr. For clusters older than 5 Myr, photometry and spectroscopy measurements deviate, with the latter producing older ages, due to the degeneracy of photometric models. FUV spectroscopy enables us to better constrain the stellar metallicities, a parameter that optical colors are insensitive to. Finally, the derived E(B-V) are quite similar, with a tendency for FUV spectroscopy to favor solutions with higher extinctions. The recovered masses are in agreement within a factor of 2 for all the clusters.