Universität zu Köln

Padovani, Marco ORCID: 0000-0003-2303-0096, Marcowith, Alexandre, Sanchez-Monge, Alvaro, Meng, Fanyi ORCID: 0000-0002-5927-2049 and Schilke, Peter ORCID: 0000-0003-2141-5689 (2019). Non-thermal emission from cosmic rays accelerated in H II regions. Astron. Astrophys., 630. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Radio observations at metre-centimetre wavelengths shed light on the nature of the emission of H II regions. Usually this category of objects is dominated by thermal radiation produced by ionised hydrogen, namely protons and electrons. However, a number of observational studies have revealed the existence of H II regions with a mixture of thermal and non-thermal radiation. The latter represents a clue as to the presence of relativistic electrons. However, neither the interstellar cosmic-ray electron flux nor the flux of secondary electrons, produced by primary cosmic rays through ionisation processes, is high enough to explain the observed flux densities. Aims. We investigate the possibility of accelerating local thermal electrons up to relativistic energies in H II region shocks. Methods. We assumed that relativistic electrons can be accelerated through the first-order Fermi acceleration mechanism and we estimated the emerging electron fluxes, the corresponding flux densities, and the spectral indexes. Results. We find flux densities of the same order of magnitude of those observed. In particular, we applied our model to the deep south (DS) region of Sagittarius B2 and we succeeded in reproducing the observed flux densities with an accuracy of less than 20% as well as the spectral indexes. The model also gives constraints on magnetic field strength (0.3-4 mG), density (1-9 x 10(4) cm(-3)), and flow velocity in the shock reference frame (33-50 km s(-1)) expected in DS. Conclusions. We suggest a mechanism able to accelerate thermal electrons inside H II regions through the first-order Fermi acceleration. The existence of a local source of relativistic electrons can explain the origin of both the observed non-thermal emission and the corresponding spectral indexes.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Padovani, Marco UNSPECIFIED orcid.org/0000-0003-2303-0096 UNSPECIFIED Marcowith, Alexandre UNSPECIFIED UNSPECIFIED UNSPECIFIED Sanchez-Monge, Alvaro UNSPECIFIED UNSPECIFIED UNSPECIFIED Meng, Fanyi UNSPECIFIED orcid.org/0000-0002-5927-2049 UNSPECIFIED Schilke, Peter UNSPECIFIED orcid.org/0000-0003-2141-5689 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-133704
DOI:	10.1051/0004-6361/201935919
Journal or Publication Title:	Astron. Astrophys.
Volume:	630
Date:	2019
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language DIFFUSIVE SHOCK ACCELERATION; PARTICLE-ACCELERATION; MAGNETIC-FIELD; SYNCHROTRON EMISSION; STAR-FORMATION; RADIO; ENERGY; MORPHOLOGIES; REMNANT Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/13370