Submillimeter Observations of IC 10: The Dust Properties and Neutral Carbon Content of a Low‐Metallicity Starburst

We present submillimeter observations of the Local Group, metal-poor,irregular dwarf galaxy IC 10, directly relevant to the interaction betweeninterstellar medium and star formation activity in primeval galaxies. Using theJCMT, we have observed the fine structure neutral carbon transition at 492 GHzand the rotational J=3-2 transition of 12CO and 13CO in the most massive giantmolecular cloud complex in this galaxy, IC10-SE. We find that, although theI([CII])/I(CO) ratio for this object is a factor of 4 larger than the typicalMilky Way value, its [C~I] to CO intensity ratio is I([CI])/I(CO)~18 is similar(only about 50% larger) to that of the Milky Way. Modelling of the [CII]/CO and[CI]/CO intensity ratios with metallicity indicates that, if C+ and C arechiefly produced by UV photodissociation, both ratios should increase sharplywith decreasing metallicity (and consequently diminished UV shielding; Bolatto,Jackson, and Ingalls 1999). These data then suggest a different origin for animportant fraction of C in these clouds, unrelated to photodissociation. Wehave also mapped the 850 um continuum in this region using SCUBA. Employingthese data in conjunction with KAO and IRAM measurements we find an extremelylow emissivity exponent, b~0.5. We conclude that this low exponent is mostlikely due to the destruction of small dust grains, brought about by theincreased penetration of UV radiation in the low metallicity ISM. If a low b inthe submillimeter is a general property of metal-poor systems then theinterpretation of millimeter and submillimeter surveys of high-z galaxiesshould be revised.Comment: 31 pages, 9 figures, 5 tables Prepared using AASLaTeX macros v4.0 Accepted for publication in the Astrophysical Journa