Feedback in the Antennae Galaxies (NGC 4038/9): I. High-Resolution Infrared Spectroscopy of Winds from Super Star Clusters

TL;DR

This study uses high-resolution infrared spectroscopy to analyze winds from young, massive super star clusters in the Antennae Galaxies, revealing high-velocity outflows that influence cluster evolution and dispersal.

Contribution

It provides detailed spectroscopic evidence of stellar winds and outflows in young super star clusters, highlighting their role in cluster expansion and potential dissipation.

Findings

Most clusters exhibit supersonic, non-Gaussian Br-gamma emission lines.

High-velocity gas exceeds escape velocities, indicating outflows.

Older clusters tend to be more compact, suggesting survival bias.

Abstract

We present high-resolution (R ~ 24,600) near-IR spectroscopy of the youngest super star clusters (SSCs) in the prototypical starburst merger, the Antennae Galaxies. These SSCs are young (3-7 Myr old) and massive (10^5 - 10^7 M_sun for a Kroupa IMF) and their spectra are characterized by broad, extended Br-gamma emission, so we refer to them as emission-line clusters (ELCs) to distinguish them from older SSCs. The Brgamma lines of most ELCs have supersonic widths (60-110 km/s FWHM) and non-Gaussian wings whose velocities exceed the clusters' escape velocities. This high-velocity unbound gas is flowing out in winds that are powered by the clusters' massive O and W-R stars over the course of at least several crossing times. The large sizes of some ELCs relative to those of older SSCs may be due to expansion caused by these outflows; many of the ELCs may not survive as bound stellar systems, but rather dissipate rapidly into the field population. The observed tendency of older ELCs to be more compact than young ones is consistent with the preferential survival of the most concentrated clusters at a given age.