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Dust properties and distribution in dwarf galaxies

Published online by Cambridge University Press:  01 June 2008

Ute Lisenfeld ,
Monica Relaño ,
José Vílchez ,
Eduardo Battaner  and
Israel Hermelo
Ute Lisenfeld
Affiliation:
Universidad Granada, Spain email: [email protected], [email protected] Institute of Astronomy, University of Cambridge, UK email: [email protected]
Monica Relaño
Affiliation:
Universidad Granada, Spain email: [email protected], [email protected] Institute of Astronomy, University of Cambridge, UK email: [email protected]
José Vílchez
Affiliation:
Instituto de Astrofísica de Andalucía, Granada, Spain email: [email protected]
Eduardo Battaner
Affiliation:
Universidad Granada, Spain email: [email protected], [email protected]
Israel Hermelo
Affiliation:
Universidad Granada, Spain email: [email protected], [email protected]
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Abstract

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We present a study of the extinction, traced by the Balmer decrement, in HII regions in the dwarf galaxies NGC 1569 and NGC 4214. We find that the large-scale extinction around the most prominent HII regions in both galaxies forms a shell in which locally the intrinsic extinction can adopt relatively high values (AV = 0.8 − 0.9 mag) despite the low metallicity and thus the low overall dust content. The small-scale extinction (spatial resolution ~0.3″) shows fluctuations that are most likely due to variations in the dust distribution. We compare the distribution of the extinction to that of the dust emission, traced by Spitzer emission at 8 and 24μm, and to the emission of cold dust at 850μm. We find in general a good agreement between all tracers, except for the 850μm emission in NGC 4214 which is more extended than the extinction and the other emissions. Whereas in NGC 1569 the dust emission at all wavelengths is very similar, NGC 4214 shows spatial variations in the 24-to-850μm ratio.

We furthermore compared the 24μm and the extinction-corrected Hα emission from HII regions in a sample of galaxies with a wide range of metallicities and found a good correlation, independent of metallicity. We suggest that this lack of dependence on metallicity might be due to the formation of dust shells with a relatively constant opacity, like the ones observed here, around ionizing stars.

Keywords

ISM: dustISM: extinctiongalaxies: ISMgalaxies: individual (NGC 1569)galaxies: individual (NGC 4214)galaxies: dwarf
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Issue S255: Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies , June 2008 , pp. 260 - 264
Copyright
Copyright © International Astronomical Union 2008

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