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Strong Evidence of Anomalous Microwave Emission from the Flux Density Spectrum of M31

Battistelli, E. S. and Fatigoni, S. and Murgia, M. and Buzzelli, A. and Carretti, E. and Castangia, P. and Concu, R. and Cruciani, A. and de Bernardis, P. and Genova-Santos, R. and Govoni, F. and Guidi, F. and Lamagna, L. and Luzzi, G. and Masi, S. and Melis, A. and Paladini, R. and Piacentini, F. and Poppi, S. and Radiconi, F. and Rebolo, R. and Rubino-Martin, J. A. and Tarchi, A. and Vacca, V. (2019) Strong Evidence of Anomalous Microwave Emission from the Flux Density Spectrum of M31. Astrophysical Journal Letters, 877 (2). Art. No. L31. ISSN 2041-8213. doi:10.3847/2041-8213/ab21de.

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We have observed the Andromeda galaxy, Messier 31 (M31), at 6.7 GHz with the Sardinia Radio Telescope. We mapped the radio emission in the C-band, re-analyzed WMAP and Planck maps, as well as other ancillary data, and we have derived an overall integrated flux density spectrum from the radio to the infrared. This allowed us to estimate the emission budget from M31. Integrating over the whole galaxy, we found strong and highly significant evidence for anomalous microwave emission (AME), at the level of 1.45_(-0.19)^(+0.17) Jy at the peaking frequency of ≃ 25 GHz. Decomposing the spectrum into known emission mechanisms such as free–free, synchrotron, thermal dust, and AME arising from electric dipole emission from rapidly rotating dust grains, we found that the overall emission from M31 is dominated, at frequencies below 10 GHz, by synchrotron emission with a spectral index of -1.10_(-0.08)^(+0.10), with subdominant free–free emission. At frequencies ≳ 10 GHz, AME has a similar intensity to that of synchrotron and free–free emission, overtaking them between 20 and 50 GHz, whereas thermal dust emission dominates the emission budget at frequencies above 60 GHz, as expected.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Battistelli, E. S.0000-0001-5210-7625
Murgia, M.0000-0002-4800-0806
Carretti, E.0000-0002-3973-8403
de Bernardis, P.0000-0001-6547-6446
Genova-Santos, R.0000-0001-5479-0034
Govoni, F.0000-0003-3644-3084
Masi, S.0000-0001-5105-1439
Paladini, R.0000-0002-5158-243X
Piacentini, F.0000-0002-5444-9327
Rebolo, R.0000-0003-3767-7085
Rubino-Martin, J. A.0000-0001-5289-3021
Additional Information:© 2019. The American Astronomical Society. Received 2019 April 10; revised 2019 May 15; accepted 2019 May 16; published 2019 May 31. The SRT is funded by the Ministry of Universities and Research, the Italian Space Agency, and the Autonomous Region of Sardinia (RAS), and is operated as a National Facility by INAF. These observations could not have been made without the continuous support of the SRT observers and technical staff. We acknowledge the financial support of Sapienza Ateneo-2016 funding. We acknowledge the use of the Planck Legacy Archive ( and of the Legacy Archive for Microwave Background Data Analysis ( This research made use of the CATS Database ( We thank S. Righini for support in preparing the observing proposal and J. Fritz for the calibrated Herschel maps. R.G.S., F.G., and J.A.R.M. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (project AYA2017-84185-P). A.M. thanks the RAS for financial support in the context of the research project CRP 18 (P.I. of the project: Dr. M. Burgay). We acknowledge the Scientific Editorial Service of the Instituto de Astrofisica de Canarias. We would like to thank the anonymous referee for the useful comments which improved the Letter.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR)UNSPECIFIED
Agenzia Spaziale Italiana (ASI)UNSPECIFIED
Autonomous Region of SardiniaCRP 18
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Sapienza UniversityAteneo-2016
Ministerio de Economía y Competitividad (MINECO)AYA2017-84185-P
Subject Keywords:galaxies: individual (M31) ; galaxies: ISM; galaxies: photometry
Issue or Number:2
Record Number:CaltechAUTHORS:20190531-091630869
Persistent URL:
Official Citation:E. S. Battistelli et al 2019 ApJL 877 L31
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95971
Deposited By: George Porter
Deposited On:31 May 2019 17:25
Last Modified:16 Nov 2021 17:17

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