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arXiv · 2511.17268

Far-infrared to centimeter emission of very nearby galaxies with archival data

L. Correia·C. Bot·J. Chastenet·A. Rymar·R. Paladini·M. Bethermin·D. Ismail·K. A. Lutz·J. -P. Bernard·A. Hughes·D. Paradis·N. Ysard
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Abstract

Compared to the well-studied infrared and radio domains, galaxy emission in the millimeter (mm) - centimeter (cm) range has been less observed. In this domain, galaxy emission consists of thermal dust, free-free and synchrotron emissions with a possible additional contribution from anomalous microwave emission (AME) peaking near 1 cm.The aim of this study is to accurately characterize the integrated spectral energy distribution (SED) of galaxies in the mm-cm range. We used COBE-DIRBE, IRAS, Planck, and WMAP all-sky surveys, brought to the same resolution of $1^\circ$, to cover 18 photometric bands from 97$μ$m to 1.3 cm. Given the low angular resolution and mixing with foreground and background emission that hampers the detection of the galaxy, our sample consists of 6 of the brightest, nearby galaxies: LMC, SMC, M31, M33, NGC 253 and NGC 4945. We subtract Milky Way dust emission, distant unresolved galaxies, and foreground point sources in the fields. We fit each integrated SED with a model of thermal dust, free-free, synchrotron, AME and Cosmic Microwave Background (CMB) temperature fluctuations. The integrated SEDs of our sample of galaxies are well fitted by the model within the uncertainties, although degeneracies between the different components contributing to the mm-cm emission complicate the estimation of their individual contributions. We do not clearly detect AME in any of our target galaxies, and AME emissivity upper limits are weak compared to Galactic standards, suggesting that the signal of AME might be diluted at the scale of a whole galaxy. We infer positive CMB fluctuations in the background of 5 out of our 6 galaxies. This effect might be related to the degeneracy between the dust emissivity index and CMB fluctuations in the background, or linked to the specific spatial distribution of CMB fluctuations coupled with the low resolution and small number statistics.

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L. Correia, C. Bot, J. Chastenet, A. Rymar, R. Paladini, M. Bethermin, D. Ismail, K. A. Lutz, J. -P. Bernard, A. Hughes, D. Paradis, N. Ysard. 2025-11-21. Far-infrared to centimeter emission of very nearby galaxies with archival data. https://doi.org/10.1051/0004-6361%2F202557211

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