The C-Band All-Sky Survey (C-BASS): new constraints on the integrated radio spectrum of M 31

ABSTRACT The Andromeda galaxy (M 31) is our closest neighbouring spiral galaxy, making it an ideal target for studying the physics of interstellar medium in a very similar to own. Using new observations M 31 at 4.76 GHz by C-Band All-Sky Survey (C-BASS), and all available radio data 1° resolution, we produce integrated spectrum put constraints on synchrotron spectral index anomalous microwave emission (AME) from 31. We use aperture photometry modelling fit 31, subtract comprehensive model nearby background sources. AME detected 3σ significance with peak near 30 flux density 0.27 ± 0.09 Jy. flatter than own Galaxy α =−0.66 0.03 no strong evidence curvature. emissivity averaged over total lower typical sources Galaxy, implying that not uniformly distributed throughout instead likely confined sub-regions – this will need be confirmed using future higher resolution around 20–30 GHz.