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, irreg ular dwarf galaxy IC 10, directly relevant to the interaction between inter stellar medium (ISM) and star formation activity in primeval galaxies. Usin g the James Clerk Maxwell Telescope, we have observed the fine-structure ne utral carbon transition P-3(1) --> P-3(0) at 492 GHz and the rotational J = 3 --> 2 transition of (CO)-C-12 and (CO)-C-13, the most massive giant mole cular cloud complex in this galaxy, IC 10-SE. We find that, although the IC I-[CII]/I-CO ratio for this object is a factor of 4 larger than the typica l Milky Way value, its [C I] to CO intensity ratio I-[C I]/I-CO similar or equal to 18 +/- 2 (in units of ergs s(-1) cm(-2) sr(-1)) is similar (only a bout 50% larger) to that of the Milky Way. Modelling of the behavior of the [C II]/CO and [C I]/CO intensity ratios with metallicity indicates that, i f C+ and C-0 are chiefly produced by UV photodissociation in the hotodissoc iation region, both ratios should increase sharply with decreasing metallic ity (and consequently diminished UV shielding). These data then suggest a d ifferent origin for an important fraction of CO in these clouds, unrelated to photodissociation. We have also mapped the 850 mu m continuum in this re gion using the Submillimetre Common User Bolometer Array. Employing these d ata in conjunction with KAO and IRAM measurements we find that the 100-1300 mu m continuum emission corresponds to a graybody with an extremely low em issivity exponent, beta similar to 0.5. We conclude that this low exponent is most likely due to the destruction of small dust grains, brought about b y the increased penetration of UV radiation in the low-metallicity ISM. If a low emissivity exponent in the submillimeter is a general property of met al-poor systems, then the interpretation of millimeter and submillimeter su rveys of high-z galaxies should be revised.