Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-02-14
Astronomy and Astrophysics
Astrophysics
4 pages, accepted to A&A Letters
Scientific paper
10.1051/0004-6361:200500024
We present a 39 h integration with the Odin satellite on the ground-state 118.75 GHz line of O2 towards the region of strongest molecular emission in the Small Magellanic Cloud. Our 3sigma upper limit to the O2 integrated intensity of <0.049 K km/s in a 9'(160 pc) diameter beam corresponds to an upper limit on the O2/H2 abundance ratio of <1.3E-6. Although a factor of 20 above the best limit on the O2 abundance obtained for a Galactic source, our result has interesting implications for understanding oxygen chemistry at sub-solar metal abundances. We compare our abundance limit to a variety of astrochemical models and find that, at low metallicities, the low O2 abundance is most likely produced by the effects of photo-dissociation on molecular cloud structure. Freeze-out of molecules onto dust grains may also be consistent with the observed abundance limit, although such models have not yet been run at sub-solar initial metallicities.
Booth Roy S.
Frisk Urban
Hjalmarson Å..
Olberg Michael
Olofsson A. O. H.
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