GTC long-slit spectroscopy of compact stellar clusters in M81

TL;DR

This study uses GTC long-slit spectroscopy to determine the ages and masses of four compact stellar clusters in M81, revealing they are young, less massive than 10^5 Msun, and among the brightest in the galaxy.

Contribution

First spectroscopic age and mass estimates for CSCs in M81, showing they are young and less massive than previously expected for such bright objects.

Findings

All clusters are 5-6 Myr old.

Masses range from 3,000 to 18,000 Msun.

No evidence of massive (10^5 Msun) clusters in M81.

Abstract

We here present the ages of four compact stellar clusters (CSCs) in the nearby spiral galaxy M81, using long-slit optical spectra obtained with the 10.4-m Gran Telescopio Canarias (GTC). All the four CSCs, including the brightest in this galaxy, are found to have ages between 5 to 6 Myr, with one of them showing Wolf-Rayet spectral features. The photometric masses of these clusters, calculated using their spectroscopically-derived ages, lie between 3000 and 18000 Msun. The observed clusters are among the brightest objects, and hence the most massive, in the entire disk of M81. This implies the absence of massive (1.0e5 Msun) compact stellar clusters in M81.