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arXiv · 2511.02061

GMCs and Star Formation in the Galaxy: I. Effects of an HII region on a GMC

David Hollenbach·Antonio Parravano·Christopher McKee
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Abstract

The destruction of Giant Molecular Clouds is a key component in galaxy evolution. We theoretically model the destruction of GMCs by HII regions, which evaporate ionized gas and eject neutral gas during their expansion. HII regions follow one of three tracks, depending on the EUV luminosity, $S$, of the ionizing OB association: the expansion can stall inside the cloud; it can break out, forming a blister (champagne) flow; or, for $S>S_{\rm com}$, it can result in the formation of a cometary cloud. We present results for the accumulated mass loss, $M_{\rm loss}(t)$, and the final mass loss, $M_{{\rm loss},f}$, by evaporation and ejection for a range of cloud masses ($10^4 S_{\rm com}$ associations destroy at least 70% of the initial cloud. We find a critical cloud mass $M_{\rm survive}$ above which clouds never become cometary and lose $<$ 70% of their mass via a single association. Low mass clouds mostly lose mass via ejection of neutral gas.

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David Hollenbach, Antonio Parravano, Christopher McKee. 2025-11-03. GMCs and Star Formation in the Galaxy: I. Effects of an HII region on a GMC. https://arxiv.org/abs/2511.02061

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