Chemical evolution of a young super star cluster at the Sunburst Arc

Abstract

Recent observations of high-redshift galaxies have revealed starburst galaxies with excessive amounts of nitrogen, well above that expected in standard evolutionary models. The Sunburst Arc galaxy, particularly its young and massive star cluster, represents the closest (z = 2.4) and brightest of these as a strongly lensed object. In this work, we study the chemical history of this star cluster to determine the origin of the elevated gas-phase nitrogen using a chemical evolution model. Our model includes the enrichment of OB stars through stellar winds and core-collapse supernovae assuming that massive stars (M > 25 M⊙) collapse directly into black holes at the end of their lives. We fit the model parameters to the observed chemical abundances of the Sunburst Arc cluster: O/H, C/O, and N/O. We find that the observed chemical abundances can be explained by models featuring intense star formation events, characterized by rapid gas accretion and high star formation efficiencies. Additionally, the stellar population contributing to the gas enrichment must exclude Wolf-Rayet stars. These conditions might be present in other nitrogen-rich objects as their similar chemical abundances suggest a common history. As previous studies have proposed the presence of Wolf-Rayet stars in the new nitrogen-rich objects, further research using chemodynamic modeling is necessary to ascertain the true nature of these objects.