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Chemical enrichment from massive stars in starbursts

Published online by Cambridge University Press:  25 May 2016

Henry A. Kobulnicky
Henry A. Kobulnicky*
Affiliation:
University of California Santa Cruz, Lick Observatory, Santa Cruz, CA 95064, USA

Abstract

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The warm ionized gas in low-mass, metal-poor star forming galaxies is chemically homogeneous despite the prevalence of large H II regions which contain hundreds of evolved massive stars, supernovae, and Wolf-Rayet stars with chemically-enriched winds. Galaxies with large WR star content are chemically indistinguishable from other vigorously star-forming galaxies. Furthermore, no significant localized chemical fluctuations are present in the vicinity of young star clusters, despite large expected chemical yields of massive stars. An ad hoc fine-tuning of the release, dispersal and mixing of the massive star ejecta could give rise to the observed homogeneity, but a more probable explanation is that fresh ejecta from massive stars reside in a hard-to-observe hot or cold phase. In any case, the observed chemical homogeneity indicates that heavy elements which have already mixed with the warm interstellar medium (thus accessible to optical spectroscopy) are homogeneously dispersed over scales exceeding 1 kpc. Mixing of fresh ejecta with the surrounding warm ISM apparently requires longer than the lifetimes of typical H II regions (> 107 yr). The lack of observed localized chemical enrichments is consistent with a scenario whereby freshly-synthesized metals from massive stars are expelled into the halos of galaxies in a hot, 106 K phase by supernova-driven winds before they cool and ‘rain’ back down upon the galaxy, creating gradual enrichments on spatial scales >1 kpc.

Type
Part 6. Starbursts in normal and active galaxies: their effects on the ISM and on chemical evolution
Information
Symposium - International Astronomical Union , Volume 193: Wolf-Rayet Phenomena in Massive Stars and Starburst Galaxies , 1999 , pp. 670 - 678
Copyright
Copyright © Astronomical Society of the Pacific 1999 

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