The small magellanic cloud in the far infrared - II. Global properties

We present global IR properties of the Small Magellanic Cloud using an ISOPHOT 170 mum map and re-visited IRAS data. The integrated 170 mum flux is 14950+/-2300 Jy, and the integrated IR flux is F1-1000=7.48x10(-10) W m(-2). Discrete sources contribute 28%, 29%, and 36% to the integrated flux at 60 mum, 100 mum, and 170 mum, respectively. Most of the total emission arises from diffuse emission regions surrounding the HII regions. The SED can be modelled by the composition of a 45 K, a 20.5 K and a 10 K blackbody component with emissivity index n=2. A color temperature map is constructed from the ISOPHOT 170 mum and the IRAS 100 mum HiRes maps. The average dust temperature is T-D=20.3 K. The total dust mass is found to be M-D=7.8x10(5) M-circle dot, yielding a gas-to-dust mass ratio M-gas/M(dust)approximate to540, a value 25 times lower than found by former studies. The global star formation rate is estimated to SFR(total)approximate to0.05 M-circle dot yr(-1). The comparison with other irregular galaxies reveals the SMC as quiet with no peculiar FIR properties.