Submillimeter observations of IC 10 : the dust properties andneutral carbon content of a low metallicity starburstAlberto

We present submillimeter observations of the Local Group, metal-poor, irregular dwarf galaxy IC 10, directly relevant to the interaction between interstellar medium and star formation activity in primeval galaxies. Using the JCMT, we have observed the ne structure neutral carbon transition 3 P 1 ! 3 P 0 at 492 GHz and the rotational J = 3 ! 2 transition of 12 CO and 13 CO in the most massive giant molecular cloud complex in this galaxy, IC 10-SE. We nd that, although the I CII] =I CO ratio for this object is a factor of 4 larger than the typical Milky Way value, its C I] to CO intensity ratio I CI] =I CO ' 18 2 (in units of erg s ?1 cm ?2 sr ?1) is similar (only about 50% larger) to that of the Milky Way. Modelling of the behaviour of the C II]/CO and C I]/CO intensity ratios with metallicity indicates that, if C + and C 0 are chieey produced by UV photodissociation in the PDR, both ratios should increase sharply with decreasing metallicity (and consequently diminished UV shielding; Bolatto, Jackson, & Ingalls 1999). These data then suggest a diierent origin for an important fraction of C 0 in these clouds, unrelated to photodissociation. We have also mapped the 850 m continuum in this region using SCUBA. Employing these data in conjunction with KAO and IRAM measurements we nd that the 100 m to 1300 m continuum emission corresponds to a graybody with an extremely low emissivity exponent, 0:5. We conclude that this low exponent is most likely due to the destruction of small dust grains, brought about by the increased penetration of UV radiation in the low metallicity ISM. If a low emissivity exponent in the submillimeter is a general property { 2 { of metal-poor systems then the interpretation of millimeter and submillimeter surveys of high-z galaxies should be revised.