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

Harper, Stuart E.; Barr, Adam; Dickinson, C.; Peel, M. W.; Cepeda-Arroita, Roke; Copley, C. J.; Grumitt, R. D. P.; Leahy, J. Patrick; Jonas, J. L.; Jones, Michael E.; Leech, J.; Pearson, T. J.; Readhead, A. C. S.; Taylor, Angela C.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society

Advertised on:
Number of authors
IAC number of authors
Refereed citations
The Andromeda galaxy (M 31) is our closest neighbouring spiral galaxy, making it an ideal target for studying the physics of the interstellar medium in a galaxy very similar to our own. Using new observations of M 31 at 4.76 GHz by the C-Band All-Sky Survey (C-BASS), and all available radio data at 1° resolution, we produce the integrated spectrum and put new constraints on the synchrotron spectral index and anomalous microwave emission (AME) from M 31. We use aperture photometry and spectral modelling to fit for the integrated spectrum of M 31, and subtract a comprehensive model of nearby background radio sources. The AME in M 31 is detected at 3σ significance with a peak near 30 GHz and flux density 0.27 ± 0.09 Jy. The synchrotron spectral index of M 31 is flatter than our own Galaxy at α =-0.66 ± 0.03 with no strong evidence of spectral curvature. The emissivity of AME averaged over the total emission from M 31 is lower than typical AME sources in our Galaxy, implying that AME is not uniformly distributed throughout M 31 and instead is likely confined to sub-regions - this will need to be confirmed using future higher resolution observations around 20-30 GHz.
Related projects
Full-sky map showing the spatial distribution of the primary anisotropies of the Cosmic Microwave Background (generated 380,000 years after the Big Bang) derived from observations of the Planck satellite
Anisotropy of the Cosmic Microwave Background
The general goal of this project is to determine and characterize the spatial and spectral variations in the temperature and polarisation of the Cosmic Microwave Background in angular scales from several arcminutes to several degrees. The primordial matter density fluctuations which originated the structure in the matter distribution of the present
Rebolo López