Near-IR Spectroscopy and Population Synthesis of Super Star Clusters in NGC 1569

TL;DR

This study uses near-infrared spectroscopy and population synthesis models to analyze the stellar populations and ages of super star clusters in NGC 1569, revealing their dominant stellar types and evolutionary stages.

Contribution

It combines NIR spectroscopy with population synthesis modeling to determine the stellar types and ages of SSCs, providing new insights into their evolution.

Findings

SSC B is dominated by K0 supergiants.

SSC A contains a mix of blue Wolf-Rayet stars and red supergiants.

Ages are estimated at 15-18 Myr for SSC B and 18-21 Myr for SSC A.

Abstract

We present H- and K-band NIRSPEC spectroscopy of super star clusters (SSCs) in the irregular starburst galaxy NGC 1569, obtained at the Keck Observatory. We fit these photospheric spectra to NextGen model atmospheres to obtain effective spectral types of clusters, and find that the information in both H- and K-band spectra is necessary to remove degeneracy in the fits. The light of SSC B is unambiguously dominated by K0 supergiants (T_eff=4400 +- 100 K, log g=0.5 +- 0.5). The double cluster SSC A has higher T_eff (G5) and less tightly constrained surface gravity (log g=1.3 +- 1.3), consistent with a mixed stellar population dominated by blue Wolf-Rayet stars and red supergiants. We predict the time evolution of infrared spectra of SSCs using Starburst99 population synthesis models coupled with empirical stellar spectral libraries (at solar metallicity). The resulting model sequence allows us to assign ages of 15-18 Myr for SSC B and 18-21 Myr for SSC A.