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

TL;DR

This study constructs comprehensive spectral energy distributions for the Magellanic Clouds, revealing a significant excess emission at millimeter and sub-millimeter wavelengths, which impacts dust and gas mass estimates.

Contribution

It provides the first detailed global SEDs of the Magellanic Clouds across eight decades, highlighting excess emission and refining flux measurements.

Findings

Detected pronounced millimeter and sub-millimeter excess emission.

Accurately measured thermal radio fluxes and low global extinctions.

Excess emission complicates dust mass and gas-to-dust ratio estimates.

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.