THE SUBMILLIMETER STRUCTURE OF THE STARBURST NUCLEUS IN M82 - A DIFFRACTION-LIMITED 450-MU-M MAP

A diffraction-limited continuum map at 450 mu m of the central 90 x 90 arcsec(2) (similar to 1.5-kpc diameter) region of the nearby starburst galaxy M82 is presented. These data from the 15-m JCMT represent the highest resolution study (similar to 9-arcsec HPBW) yet carried out at submillimetre wavelengths of the thermal reradiated emission from dust in M82. The first continuum observations at 2 mm made at the NRAO 12-m are also presented. The 450-mu m data show a double-peaked structure, similar to that observed in various molecular line transitions and 10-30 mu m continuum maps. The variation in source size with wavelength and a major-axis intensity profile are consistent with emission from a cooler and larger scale component of the mid-IR dust torus. A spur of thermal emission, similar to that observed in H alpha and X-ray emission, is detected extending southwards from the south-western peak. An integrated 450-mu m flux density of 41 +/- 6.0 Jy is measured. When corrected for free-free emission, the FIR-millimetre continuum is well fitted by optically thin emission from anisothermal population (T = 48 K) of dust grains with an emissivity index beta = 1.3.