Journal Article

Do Environmental Conditions Affect the Dust-Induced Fragmentation in Low-Metallicity Clouds? Effect of Pre-Ionization and Far-Ultraviolet/Cosmic-Ray Fields

Kazuyuki Omukai

in Publications of the Astronomical Society of Japan

Volume 64, issue 5 Published in print October 2012 | ISSN: 0004-6264
Published online October 2012 | e-ISSN: 2053-051X | DOI: https://dx.doi.org/10.1093/pasj/64.5.114
Do Environmental Conditions Affect the Dust-Induced Fragmentation in Low-Metallicity Clouds? Effect of Pre-Ionization and Far-Ultraviolet/Cosmic-Ray Fields

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We study the effects of the fully ionized initial state, or pre-ionization, on the subsequent thermal evolution of low-metallicity clouds under various intensities of external far-ultraviolet (FUV) and cosmic-ray (CR) fields. Pre-ionization significantly affects the thermal and dynamical evolution of metal-free clouds without FUV/CRs by way of efficient HD formation. On the other hand, the pre-ionization effect on thermal evolution is limited in the very low-density regime for more metal-enriched clouds ([Z[math] H] [math] [math] 4), or those under a modest FUV ([math] 10[math] ) field or CR field ([math] 0.1) of the present-day galactic disk levels. In any case, for [math] 10[math] cm[math] , neither the initial ionization state nor the irradiating FUV strength affect the thermal evolution. The dust cooling is an important mechanism for making sub-solar mass fragments in low-metallicity gas. Since this fragmentation occurs at the temperature minimum by dust cooling at [math] 10[math] cm[math] , this process is not vulnerable either to the initial ionization state or external radiation.

Keywords: ISM: molecules; stars: formation; stars: Population II

Journal Article.  5501 words.  Illustrated.

Subjects: Stars ; Interstellar Medium

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