SAO-6m Telescope Spectroscopic Observations of Globular Clusters in Nearby Galaxies

TL;DR

This study uses medium-resolution spectroscopy to analyze globular clusters in six nearby galaxies, revealing their ages, metallicities, and element ratios, and exploring their relation to galaxy properties.

Contribution

It provides new spectroscopic measurements of GCs across diverse galaxy types, highlighting differences in metallicity and age distributions linked to galaxy mass and morphology.

Findings

Old and intermediate-age GCs are metal-poor ([Z/H] < -0.8 dex).

Metal-rich clusters are younger and found in more massive galaxies.

GC metallicity and age relations vary with galaxy mass and type.

Abstract

We present the results of medium-resolution spectroscopy of 28 globular clusters (GCs) in six nearby galaxies of different luminosities and morphological types, situated in: M33 (15 objects), M31 (3), IC10 (4), UGCA86 (4), HolmbergIX (1), and DDO71 (1) obtained at the Special Astrophysical Observatory 6-meter telescope. Measurements of Lick absorption-line indices and comparison with SSP models enabled us to obtain their spectroscopic ages, metallicities and alpha-element to Fe abundance ratios. We found that all old and intermediate-age GCs in our sample have low metallicities [Z/H] < -0.8 dex. Metal-rich clusters are young and are preferentially found in galaxies more massive than ~10^9 M_sun. The least massive dwarfs of our sample, DDO71 and HolmbergIX, host one massive intermediate-age and one massive young metal-poor GC, respectively. [a/Fe] abundance ratios tend to be enhanced but closer to solar values for dwarf galaxies compared to GCs in more massive galaxies. We analyse the age-metallicity relation for GCs in our galaxy sample and others from the literature, and find, that 1) there is a general trend for GCs in low surface brightness dwarf galaxies to be more metal-poor at a given age than GCs in more massive galaxies; 2) the GC metallicity spread is wider for more massive galaxies; 3) intermediate-age GCs in early-type dwarf galaxies are more metal-rich at any given age than those in irregular galaxies of similar luminosity.