Sub-millimeter to centimeter excess emission from the Magellanic Clouds. I. Global spectral energy distribution

Abstract

In order to reconstruct the global SEDs of the Magellanic Clouds over eight decades in spectral range, we combined literature flux densities representing the entire LMC and SMC respectively, and complemented these with maps extracted from the WMAP and COBE databases covering the missing the 23--90 GHz (13--3.2 mm) and the poorly sampled 1.25--250 THz (240--1.25 micron). We have discovered a pronounced excess of emission from both Magellanic Clouds, but especially the SMC, at millimeter and sub-millimeter wavelengths. We also determined accurate thermal radio fluxes and very low global extinctions for both LMC and SMC. Possible explanations are briefly considered but as long as the nature of the excess emission is unknown, the total dust masses and gas-to-dust ratios of the Magellanic Clouds cannot reliably be determined.