Nearby galaxies in the LOFAR Two-metre Sky Survey I. Insights into the non-linearity of the radio-SFR relation
Artikel i vetenskaplig tidskrift, 2022
Context. Cosmic rays and magnetic fields are key ingredients in galaxy evolution, regulating both stellar feedback and star formation. Their properties can be studied with low-frequency radio continuum observations that are free from thermal contamination. Aims. We define a sample of 76 nearby (<30 Mpc) galaxies with rich ancillary data in the radio continuum and infrared from the CHANG-ES and KINGFISH surveys, which will be observed with the LOFAR Two-metre Sky Survey (LoTSS) at 144 MHz. Methods. We present maps for 45 of them as part of the LoTSS data release 2 (LoTSS-DR2), where we measure integrated flux densities and study integrated and spatially resolved radio spectral indices. We investigate the radio-star formation rate (SFR) relation using SFRs derived from total infrared and H alpha + 24-mu m emission. Results. The radio-SFR relation at 144 MHz is clearly super-linear with L-144mHz proportional to SFR1,4-1,5. The mean integrated radio spectral index between 144 and approximate to 1400 MHz is = -0.56 +/- 0.14, in agreement with the injection spectral index for cosmic ray electrons (CRE5). However, the radio spectral index maps show variation of spectral indices with flatter spectra associated with star-forming regions and steeper spectra in galaxy outskirts and, in particular, in extra-planar regions. We found that galaxies with high SFRs have steeper radio spectra; we find similar correlations with galaxy size, mass, and rotation speed. Conclusions. Galaxies that are larger and more massive are better electron calorimeters, meaning that the CRE lose a higher fraction of their energy within the galaxies. This explains the super-linear radio-SFR relation, with more massive, star-forming galaxies being radio bright. We propose a semi-calorimetric radio-SFR relation that employs the galaxy mass as a proxy for the calorimetric efficiency.
galaxies: magnetic fields
cosmic rays
galaxies: halos
galaxies: fundamental parameters
radio continuum: galaxies
Författare
V Heesen
Universität Hamburg
M. Staffehl
Universität Hamburg
A. Basu
Thüringer Landessternwarte Tautenburg
R. Beck
Max-Planck-Gesellschaft
M. Stein
Ruhr-Universität Bochum
F. S. Tabatabaei
Institute for Research in Fundamental Sciences (IPM)
M. J. Hardcastle
University of Hertfordshire
K. T. Chyzy
Uniwersytet Jagiellonski w Krakowie
T. W. Shimwell
Universiteit Leiden
Netherlands Institute for Radio Astronomy (ASTRON)
B. Adebahr
Ruhr-Universität Bochum
R. Beswick
University of Manchester
D. J. Bomans
Ruhr-Universität Bochum
A. Botteon
Universiteit Leiden
E. Brinks
University of Hertfordshire
M. Brueggen
Universität Hamburg
R-J Dettmar
Ruhr-Universität Bochum
A. Drabent
Thüringer Landessternwarte Tautenburg
F. de Gasperin
Universität Hamburg
G. Guerkan
Thüringer Landessternwarte Tautenburg
G. H. Heald
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
Cathy Horellou
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
B. Nikiel-Wroczynski
Uniwersytet Jagiellonski w Krakowie
R. Paladino
Istituto nazionale di astrofisica (INAF)
J. Piotrowska
Uniwersytet Jagiellonski w Krakowie
H. J. A. Roettgering
Universiteit Leiden
D. J. B. Smith
University of Hertfordshire
C. Tasse
Université de recherche Paris Sciences et Lettres
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 664 A83Ämneskategorier
Astronomi, astrofysik och kosmologi
Atom- och molekylfysik och optik
Den kondenserade materiens fysik
DOI
10.1051/0004-6361/202142878