Embedded Young Massive Star Clusters in the Antennae Merger

• Main Authors: He, Hao, Wilson, Christine, Brunetti, Nathan, Finn, Molly, Bemis, Ashley, Johnson, Kelsey
• Format: Journal Article
• Language: English
• Published: 23-02-2022
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.2202.08077

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.