Infrared Emission from the Radio Supernebula in NGC 5253: A Proto-Globular Cluster?

TL;DR

This study reveals a highly obscured, young, dense star cluster in NGC 5253 that resembles a proto-globular cluster, based on infrared and radio observations indicating intense star formation within a compact region.

Contribution

First infrared imaging of the radio supernebula in NGC 5253, demonstrating it as a young, dense star cluster with properties similar to a proto-globular cluster.

Findings

Infrared emission confirms a dense, young star cluster.

The cluster accounts for at least 15% of the galaxy's luminosity.

Estimated age is a few hundred thousand years.

Abstract

Hidden from optical view in the starburst region of the dwarf galaxy NGC 5253 lies an intense radio source with an unusual spectrum which could be interpreted variously as nebular gas ionized by a young stellar cluster or nonthermal emission from a radio supernova or an AGN. We have obtained 11.7 and 18.7 micron images of this region at the Keck Telescope and find that it is an extremely strong mid-infrared emitter. The infrared to radio flux ratio rules out a supernova and is consistent with an HII region excited by a dense cluster of young stars. This "super nebula" provides at least 15% of the total bolometric luminosity of the galaxy. Its excitation requires 10^5-10^6 stars, giving it the total mass and size (1-2 pc diameter) of a globular cluster. However, its high obscuration, small size, and high gas density all argue that it is very young, no more than a few hundred thousand years old. This may be the youngest globular cluster yet observed.