The Molecular Front in Galaxies II : Galactic-scale Gas Phase Transition of HI and H2

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dc.creatorHonma, Mareki
dc.creatorSofue, Yoshiaki
dc.creatorArimoto, Nobuo
dc.date1995-07-25
dc.date.accessioned2026-07-07T02:19:56Z
dc.date.available2026-07-07T02:19:56Z
dc.descriptionWe have examined the distribution of HI and H$_2$ gases in four face-on galaxies by using the observed dat a of CO and HI line emissions from the literatures. We demonstrate that the gas phase transition of HI and H$_2$ occurs suddenly within a narrow range of radi us, which we call the molecular front. We have tried to explain such phase transition in galactic scale with a help of the phase transition theory proposed by Elmegreen. The crucial parameters for determinating the molecular fraction $f_{\rm mol}$ are interstellar pressure $P $, UV radiation field $U$, and metallicity $Z$, and we have constructed a model galaxy in which $P$, $U$ a nd $Z$ obey an exponential function of the galacto-centric radius. The model shows that the molecular front must be a fundamental feature of galaxies which has an exponentia l disk, and that the metallicity gradient is most crucial for the formation of the molecular front. We have also tried to reproduce the observed molecular fraction $f_{\rm mol}$ by giving the set of ($P$, $ U$, $Z$) observationally, and show that the model can describe the variation of the molecular fraction $f_ {\rm mol}$ in galaxies quite well. We discuss the implication of the molecular front for the chemical evolution of galaxies.
dc.descriptionLatex, 16 pages, Figures on request, To appear in AA
dc.identifierhttps://arxiv.org/abs/astro-ph/9507099
dc.identifierhttp://arxiv.org/abs/astro-ph/9507099
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/10062
dc.subjectAstrophysics
dc.titleThe Molecular Front in Galaxies II : Galactic-scale Gas Phase Transition of HI and H2
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