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Low Metallicity ISM: excess submillimetre emission and CO-free H2 gas

Published online by Cambridge University Press:  17 August 2012

Suzanne C. Madden ,
Aurélie Rémy ,
Frédéric Galliano ,
Maud Galametz ,
George Bendo ,
Diane Cormier ,
Vianney Lebouteiller  and
Sacha Hony
Suzanne C. Madden
Affiliation:
CEA Saclay, DSM, AIM, Service d'Astrophysique, Gif-sur-Yvette 91911, France email: [email protected]
Aurélie Rémy
Affiliation:
CEA Saclay, DSM, AIM, Service d'Astrophysique, Gif-sur-Yvette 91911, France email: [email protected]
Frédéric Galliano
Affiliation:
CEA Saclay, DSM, AIM, Service d'Astrophysique, Gif-sur-Yvette 91911, France email: [email protected]
Maud Galametz
Affiliation:
Institute of Astronomy, University of Cambridge, Madingly Rd., Cambridge, UK
George Bendo
Affiliation:
Alma Regional Center, University of Manchester, Oxford Rd., Manchester, UK
Diane Cormier
Affiliation:
CEA Saclay, DSM, AIM, Service d'Astrophysique, Gif-sur-Yvette 91911, France email: [email protected]
Vianney Lebouteiller
Affiliation:
CEA Saclay, DSM, AIM, Service d'Astrophysique, Gif-sur-Yvette 91911, France email: [email protected]
Sacha Hony
Affiliation:
CEA Saclay, DSM, AIM, Service d'Astrophysique, Gif-sur-Yvette 91911, France email: [email protected]
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Abstract

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The low metallicity interstellar medium of dwarf galaxies gives a different picture in the far infrared(FIR)/submillimetre(submm)wavelengths than the more metal-rich galaxies. Excess emission is often found in the submm beginning at or beyond 500 μm. Even without taking this excess emission into account as a possible dust component, higher dust-to-gas mass ratios (DGR) are often observed compared to that expected from their metallicity for moderately metal-poor galaxies. The Spectral Energy Distributions (SEDs) of the lowest metallicity galaxies, however, give very low dust masses and excessively low values of DGR, inconsistent with the amount of metals expected to be captured into dust if we presume the usual linear relationship holding for all metallicities, including the more metal-rich galaxies. This transition seems to appear near metalllicities of 12 + log(O/H) 8.0 - 8.2. These results rely on accurately quantifying the total molecular gas reservoir, which is uncertain in low metallicity galaxies due to the difficulty in detecting CO(1-0) emission. Dwarf galaxies show an exceptionally high [CII] 158 μm/CO (1-0) ratio which may be indicative of a significant reservoir of ‘CO-free’ molecular gas residing in the photodissociated envelope, and not traced by the small CO cores.

Keywords

galaxies: dwarfgalaxies: ISMISM: molecules
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 7 , Symposium S284: The Spectral Energy Distribution of Galaxies , September 2011 , pp. 141 - 148
Copyright
Copyright © International Astronomical Union 2012

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