The submillimetre structure of the starburst nucleus in M82: a diffraction-limited 450-μm map

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Abstract
A diffraction-limited continuum map at 450 μm of the central 90 × 90 arcsec2 ( ~ 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 ( ~ 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-μm data show a double-peaked structure, similar to that observed in various molecular line transitions and 10–30 μm 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 α and X-ray emission, is detected extending southwards from the south-western peak. An integrated 450-μm 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 an isothermal population (T = 48 K) of dust grains with an emissivity index: β = 1.3.

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