Journal Article

Metals, dust and the cosmic microwave background: fragmentation of high-redshift star-forming clouds

Raffaella Schneider and Kazuyuki Omukai

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 1, pages 429-435
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI:

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We investigate the effects of the cosmic microwave background (CMB) radiation field on the collapse of pre-stellar clouds. Using a semi-analytic model to follow the thermal evolution of clouds with varying initial metallicities and dust contents at different redshifts, we study self-consistently the response of the mean Jeans mass at cloud fragmentation to metal line cooling, dust cooling and the CMB.

In the absence of dust grains, at redshifts z≤ 10 moderate characteristic masses (of tens of M) are formed when the metallicity is 10−4 ZZ≤ 10−2.5 Z; at higher metallicities, the CMB inhibits fragmentation and only very large masses (of approximately hundreds of M) are formed. These effects become even more dramatic at z > 10 and the fragmentation mass scales are always ≥hundreds of M, independent of the initial metallicity.

When dust grains are present, sub-solar mass fragments are formed at any redshift for metallicities Z≥ 10−6 Z because dust cooling remains relatively insensitive to the presence of the CMB. When Z > 10−3 Z, heating of dust grains by the CMB at z≥ 5 favours the formation of larger masses, which become super-solar when Z≥ 10−2 Z and z≥ 10. Finally, we discuss the implications of our result for the interpretation of the observed abundance patterns of very metal-poor stars in the Galactic halo.

Keywords: stars: formation; stars: Population II; ISM: abundances; galaxies: evolution; cosmic microwave background

Journal Article.  5366 words.  Illustrated.

Subjects: Astronomy and Astrophysics