Gum 48d: an evolved HII region with ongoing star formation

TL;DR

Gum 48d is an evolved HII region with ongoing star formation, illustrating a later stage in HII region evolution characterized by a ring-like morphology and multiple generations of star formation over 10 million years.

Contribution

This study provides a detailed multi-wavelength analysis of Gum 48d, revealing its evolutionary history and ongoing star formation, which enhances understanding of late-stage HII region development.

Findings

Gum 48d has a ring-like morphology with diffuse PDR emission.

Ongoing star formation occurs at multiple mass scales.

The region's evolution spans approximately 10 million years.

Abstract

High mass star formation and the evolution of HII regions have a substantial impact on the morphology and star formation history of molecular clouds. The HII region Gum 48d, located in the Centaurus Arm at a distance of 3.5 kpc, is an old, well evolved HII region whose ionizing stars have moved off the main sequence. As such, it represents a phase in the evolution of HII regions that is less well studied than the earlier, more energetic, main sequence phase. In this paper we use multi-wavelength archive data from a variety of sources to perform a detailed study of this interesting region. Morphologically, Gum 48d displays a ring-like faint HII region associated with diffuse emission from the associated PDR, and is formed from part of a large, massive molecular cloud complex. There is extensive ongoing star formation in the region, at scales ranging from low to high mass, which is consistent with triggered star formation scenarios. We investigate the dynamical history and evolution of this region, and conclude that the original HII region was once larger and more energetic than the faint region currently seen. The proposed history of this molecular cloud complex is one of multiple, linked generations of star formation, over a period of 10 Myr. Gum 48d differs significantly in morphology and star formation that the other HII regions in the molecular cloud; these differences are likely the result of the advanced age of the region, and its different evolutionary status.