UV star-forming regions in M31

We use Galaxy Evolution Explorer (GALEX) far-UV (1344-1786{AA}, FUV) and near-UV (1771-2831{AA}, NUV) imaging to detect young massive stars and trace the recent star formation across the galaxy. The FUV and NUV flux measurements of the SF regions, combined with ground-based data for estimating the reddening by interstellar dust from the massive stars they contain, are used to derive their ages and masses.

The GALEX imaging, combining deep sensitivity and coverage of the entire galaxy, provides a complete picture of the recent star formation in M31 and its variation with environment throughout the galaxy. The FUV and NUV measurements are sensitive to detect stellar populations younger than a few hundred Myr. We detected 894 SF regions, with size >=1600pc^2^ above an average FUV flux limit of ~26ABmag/arcsecond^2^, over the whole 26kpc (radius) galaxy disk.