The Small Magellanic Cloud in the far infrared. II. Global properties

Abstract

We present global IR properties of the Small Magellanic Cloud using an ISOPHOT 170 μm map and re-visited IRAS data. The integrated 170 μm flux is 14 950 ± 2300 Jy, and the integrated IR flux is F_1-1000 = 7.48 × 10^-10 W m^-2. Discrete sources contribute 28%, 29%, and 36% to the integrated flux at 60 μm, 100 μm, and 170 μm, 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 μm and the IRAS 100 μm HiRes maps. The average dust temperature is T_D = 20.3 K. The total dust mass is found to be M_D = 7.8× 10⁵ M_⊙, yielding a gas-to-dust mass ratio M_gas/M_dust ≈ 540, a value 25 times lower than found by former studies. The global star formation rate is estimated to SFR_total ≈ 0.05 M_⊙ yr^-1. The comparison with other irregular galaxies reveals the SMC as quiet with no peculiar FIR properties.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) and with the participation of ISAS and NASA.