A photodissociation model for the morphology of the HI near OB associations in M33

TL;DR

This paper models the HI morphology near OB associations in M33 as resulting from photodissociation of molecular gas, providing insights into the interaction between UV radiation and GMCs in galaxy environments.

Contribution

It introduces a novel photodissociation model explaining HI features near OB associations in M33, supported by detailed observational analysis.

Findings

Evidence of UV radiation diffusion through clumpy GMCs

Enhanced CO emission linked to higher density GMCs

First detailed analysis of HI near OB associations in M33

Abstract

We present an approach for analysing the morphology and physical properties of Hi features near giant OB asso- ciations in M33, in the context of a model whereby the Hi excess arises from photodissociation of the molecular gas in remnants of the parent Giant Molecular Clouds (GMCs). Examples are presented here in the environs of NGC604 and CPSDPZ204, two prominent Hii regions in M33. These are the first results of a detailed analysis of the environs of a large number of OB associations in that galaxy. We present evidence for "diffusion" of the far-UV radiation from the OB association through a clumpy remnant GMC, and show further that enhanced CO(1-0) emission appears preferentially associated with GMCs of higher volume density.