Ultra-compact Embedded Clusters in the Galactic Plane

TL;DR

This paper reports the discovery of a new population of ultra-compact, embedded low-mass stellar clusters in the Galactic Plane, characterized by their small size, infrared brightness, and association with molecular clouds, expanding our understanding of star formation.

Contribution

The study introduces a catalog of 18 ultra-compact embedded clusters identified via infrared surveys, revealing a previously unrecognized population of low-mass stellar groupings.

Findings

Identified 18 ultra-compact embedded clusters in the Galactic Plane.

Clusters contain about six stars each, with associated molecular material.

Potential progenitors of Herbig Ae/Be pre-main sequence clusters.

Abstract

We have identified a previously unrecognized population of very compact, embedded low-mass Galactic stellar clusters. These tight (r$ \approx $0.14 pc) groupings appear as bright singular objects at the few arcsec resolution of the Spitzer Space Telescope at 8 and 24 $\mu$m but become resolved in the sub-arcsecond UKIDSS images. They average six stars per cluster surrounded by diffuse infrared emission and coincide with 100 -- 300 M$_{\sun}$ clumps of molecular material within a larger molecular cloud. The magnitudes of the brightest stars are consistent with mid- to early-B stars anchoring $\sim$80 M$_{\sun}$ star clusters. Their evolutionary descendants are likely to be Herbig Ae/Be pre-main sequence clusters. These ultra-compact embedded clusters (UCECs) may fill part of the low-mass void in the embedded cluster mass function. We provide an initial catalog of 18 UCECs drawn from infrared Galactic Plane surveys.