The Small Magellanic Cloud in the far infrared. I. ISO's 170 mu m map and revisit of the IRAS 12-100 mu m data

Abstract

The ISOPHOT experiment onboard the ISO satellite generated a complete view of the Small Magellanic Cloud (SMC) at 170 mu m with 1.5 arcmin resolution. The map is analysed using an automated photometry program enabling accurate photometric characterization of the far infrared (FIR) emitting regions. An integrated FIR luminosity of 8.5x 10⁷ L_sun is obtained, leading to a star formation rate of SFR_FIR=0.015 M_sun/yr. With an average dust temperature of <T_D, 170/100}=20.5 K>, the total dust mass follows to M_D=3.7x10⁵ M_sun. In this paper, the sources detected at 170 mu m are compared with those obtainable from the IRAS satellite data. For this purpose, the 12 mu m, 25 mu m, 60 mu m, and 100 mu m IRAS high resolution (HiRes) maps of the SMC are re-examined using the same method. In contrast to former studies, this provides an all-band ISO/IRAS source catalog which is no longer based on eyeball classification, but relies on an algorithm which is capable of automated, repeatable photometry, even for irregular sources. In the mid infrared IRAS bands numerous bright FIR emitting regions in the SMC are detected and classified: 73 sources are found at 12 mu m, 135 at 25 mu m (most of them with F_nu <1.0 Jy). All three FIR bands at 170 mu m, 100 mu m, and 60 mu m reproduce the overall morphological structure of the SMC similarly well, in contrast to the 12 mu m and 25 mu m maps which only contain a limited number of extended sources and do not trace the main body of the SMC. 243 sources are detected in the ISO 170 mu m map, 155 of them with F_nu >=2.0 Jy. Comparable numbers are found for the two FIR IRAS maps at 60 mu m (384) and 100 mu m (338) with fluxes up to 450 Jy. 70 of the 243 170 mu m sources are assigned a general SED type (``cold'', ``warm'', i.e., <30 K, >30 K) for the first time. A comparison with earlier IRAS results suggests that many source flux densities in those studies have been under- or overestimated because of non-standardized fitting methods. Many sources with flux densities up to 40 Jy listed in former catalogs cannot be identified in our data.

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.

The tables in Appendices A to E are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http//cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/401/873}