Nearby galaxies in the LOFAR Two-metre Sky Survey I. Insights into the non-linearity of the radio-SFR relation
Journal article, 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
Author
V Heesen
University of Hamburg
M. Staffehl
University of Hamburg
A. Basu
Thüringer Landessternwarte Tautenburg
R. Beck
Max Planck Society
M. Stein
Ruhr-Universität Bochum
F. S. Tabatabaei
Institute for Research in Fundamental Sciences (IPM)
M. J. Hardcastle
University of Hertfordshire
K. T. Chyzy
Jagiellonian University in Kraków
T. W. Shimwell
Leiden University
Netherlands Institute for Radio Astronomy (ASTRON)
B. Adebahr
Ruhr-Universität Bochum
R. Beswick
University of Manchester
D. J. Bomans
Ruhr-Universität Bochum
A. Botteon
Leiden University
E. Brinks
University of Hertfordshire
M. Brueggen
University of Hamburg
R-J Dettmar
Ruhr-Universität Bochum
A. Drabent
Thüringer Landessternwarte Tautenburg
F. de Gasperin
University of Hamburg
G. Guerkan
Thüringer Landessternwarte Tautenburg
G. H. Heald
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
Cathy Horellou
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
B. Nikiel-Wroczynski
Jagiellonian University in Kraków
R. Paladino
Istituto nazionale di astrofisica (INAF)
J. Piotrowska
Jagiellonian University in Kraków
H. J. A. Roettgering
Leiden University
D. J. B. Smith
University of Hertfordshire
C. Tasse
Université Paris PSL
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 664 A83Subject Categories
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Condensed Matter Physics
DOI
10.1051/0004-6361/202142878