The Herschel Exploitation of Local Galaxy Andromeda (HELGA) II: Dust and Gas in Andromeda

Understand

We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak.

• We fit a modified-blackbody model to ~4000 quasi-independent pixels with spatial resolution of ~140pc and find that a variable dust-emissivity index (beta) is required to fit the data.
• We find no significant long-wavelength excess above this model suggesting there is no cold dust component.
• We show that the gas-to-dust ratio varies radially, increasing from ~20 in the center to ~70 in the star-forming ring at 10kpc, consistent with the metallicity gradient.