Embedded Young Massive Star Clusters in the Antennae Merger

TL;DR

This study uses high-resolution ALMA data to analyze young massive star clusters in the Antennae galaxy, revealing their properties, formation efficiency, and relation to their parent molecular clouds in a merging galaxy environment.

Contribution

It provides the first high-resolution ALMA observations of YMCs in the Antennae, demonstrating their bound nature, young age, and significant contribution to star formation in GMCs.

Findings

Most YMCs are bound clusters with ages around 1 Myr.

Approximately 50% of free-free emission in GMCs originates from YMCs.

The mass ratio of YMCs to GMCs aligns with star cluster formation models.

Abstract

The properties of young massive clusters (YMCs) are key to understanding the star formation mechanism in starburst systems, especially mergers. We present ALMA high-resolution ($\sim$10 pc) continuum (100 and 345 GHz) data of YMCs in the overlap region of the Antennae galaxy. We identify 6 sources in the overlap region, including two sources that lie in the same giant molecular cloud (GMC). These YMCs correspond well with radio sources in lower resolution continuum (100 and 220 GHz) images at GMC scales ($\sim$60 pc). We find most of these YMCs are bound clusters through virial analysis. We estimate their ages to be $\sim$1 Myr and to be either embedded or just beginning to emerge from their parent cloud. We also compare each radio source with Pa$\beta$ source and find they have consistent total ionizing photon numbers, which indicates they are tracing the same physical source. By comparing the free-free emission at $\sim$10 pc scale and $\sim$60 pc scale, we find that $\sim$50% of the free-free emission in GMCs actually comes from these YMCs. This indicates that roughly half of the stars in massive GMCs are formed in bound clusters. We further explore the mass correlation between YMCs and GMCs in the Antennae and find it generally agrees with the predictions of the star cluster simulations. The most massive YMC has a stellar mass that is 1% - 5% of its host GMC mass.