The Youngest Globular Clusters

TL;DR

This paper reviews the formation and early development of super star clusters (SSCs) in starburst galaxies, highlighting their potential to evolve into globular clusters and discussing recent observations of their embedded phases and gas dynamics.

Contribution

It provides a comprehensive review of embedded super star clusters, their properties, and the mechanisms that may allow them to survive and evolve into globular clusters.

Findings

Embedded clusters with high star formation efficiency are likely to survive as bound clusters.

Observations show ionized gas outflows that may protect molecular clouds from feedback.

Super star clusters in starburst galaxies can evolve into globular-like objects.

Abstract

It is likely that all stars are born in clusters, but most clusters are not bound and disperse. None of the many protoclusters in our Galaxy are likely to develop into long-lived bound clusters. The Super Star Clusters (SSCs) seen in starburst galaxies are more massive and compact and have better chances of survival. The birth and early development of SSCs takes place deep in molecular clouds, and during this crucial stage the embedded clusters are invisible to optical or UV observations but are studied via the radio-infared supernebulae (RISN) they excite. We review observations of embedded clusters and identify RISN within 10 Mpc whose exciting clusters have a million solar masses or more in volumes of a few cubic parsecs and which are likely to not only survive as bound clusters, but to evolve into objects as massive and compact as Galactic globulars. These clusters are distinguished by very high star formation efficiency eta, at least a factor of 10 higher than the few percent seen in the Galaxy, probably due to violent disturbances their host galaxies have undergone. We review recent observations of the kinematics of the ionized gas in RISN showing outflows through low-density channels in the ambient molecular cloud; this may protect the cloud from feedback by the embedded HII region.