Gas, Dust and Star-Formation in Andromeda with HELGA
S. A. Eales, W. K. Gear, G. Ford, J. Fritz, M. Baes, I. De Looze, S. Madden, B O'Halloran, J. Verstappen, & SAG2 Consortium
Andromeda (M31) and the Milky Way (MW) are the two large spirals in the local group. Studies of M31 are important as unlike the MW we can obtain a complete census of all star-formation, gas and dust in the galaxy. We present results from HELGA (Herschel Exploitation of Local Galaxy Andromeda) survey which uses the PACS and SPIRE instruments to obtain photometric data of a ~5.5×2.5 degree area centred on M31. By fitting spectral energy distributions to each pixel we find a radial dependence of gas-to-dust ratio with low values of ~30 compared to the local MW value ~120. This change in dust properties in the centre also coincides with a region of increased star-formation efficiency possibly due to a starburst event. In addition we find the Far-Infrared spectral index (beta) varies from ~1.8 in the outer ring to ~2.5 in the inner regions with dust temperatures around 18K. In the very centre the spectral index drops down but the temperature increases to ~30K. We also search for evidence of 'dark gas' in Andromeda.