Abstract. We present new 450 and 850 µm SCUBA data of the dwarf galaxy NGC 1569. We construct the mid-infrared to millimeter SED of NGC 1569, using ISOCAM, ISOPHOT, IRAS, KAO, SCUBA and MAMBO data, and model the SED in order to explore the nature of the dust in low metallicity environments. The detailed modeling is performed in a selfconsistent way, synthesizing the global ISRF of the galaxy using an evolutionary synthesis model with further constraints provided by the observed MIR ionic lines and a photoionisation model. Our results show that the dust properties are different in this low metallicity galaxy compared to other more metal rich galaxies. The results indicate a paucity of PAHs probably due to the destructive effects of the ISRF penetrating a clumpy environment and a size-segregation of grains where the emission is dominated by small grains of size ∼3 nm, consistent with the idea of shocks having a dramatic effect on the dust properties in NGC 1569. A significant millimetre excess is present in the dust SED which can be explained by the presence of ubiquitous very cold dust (T = 5−7 K). This dust component accounts for 40 to 70% of the total dust mass in the galaxy (1.6−3.4 × 10 5 M ) and could be distributed in small clumps (size a few pc) throughout the galaxy. We find a gas-to-dust mass ratio of 740−1600, larger than that of the Galaxy and a dust-to-metals ratio of 1/4 to 1/7. We generate an extinction curve for NGC 1569, consistent with the modeled dust size distribution. This extinction curve has relatively steep FUV rise and smaller 2175 Å bump, resembling the observed extinction curve of some regions in the Large Magellanic Cloud.

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We have mapped the [C II] 158 km line over in the Magellanic irregular galaxy IC 10, thus 8@ .5 ] 6@ .5 presenting the Ðrst complete [C II] map of an entire low-metallicity galaxy. The total luminosity in the [C II] line in IC 10 is 1.5 ] 106We discuss the origin of the [C II] emission toward di †erent regions L _ . in the galaxy. Overall, about 10% of the [C II] emission can originate in standard H I clouds (n D 80, T D 100 K), while up to about 10% of the emission can originate in ionized gas, either the low-density warm gas or the denser H II regions. For the two brightest regions, most of the [C II] emission is associated with dense photodissociation regions (PDRs). For several regions, however, the [C II] emission may not be explained by standard PDR models. For these regions, emission solely from the atomic medium can also be precluded because the cooling rate per hydrogen atom would be much greater than the heating rate provided by photoelectric UV heating. We speculate that in these regions the presence of an additional column density of 5 times that observed in H I, is required to explain the [C II] emission. H 2 , The ambient UV Ðelds present in these regions, combined with the low metallicity, create a situation where small CO cores exist surrounded by a relatively large [C II]-emitting envelope where molecular hydrogen is self-shielded. This additional molecular mass is equivalent to at least 100 times the mass in the CO core that one would derive from the CO integrated intensity alone using the standard CO-to-H 2 conversion factor. These [C II] observations may, therefore, make a more reliable inventory of the gas reservoir in dwarf irregular galaxies where use of CO alone may signiÐcantly underestimate the molecular mass.