期刊
ASTRONOMY & ASTROPHYSICS
卷 664, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/202142878
关键词
cosmic rays; galaxies: magnetic fields; galaxies: fundamental parameters; galaxies: halos; radio continuum: galaxies
资金
- CNRS-INSU, France
- Observatoire de Paris, France
- Universite d'Orleans, France
- BMBF, Germany
- MIWF-NRW, Germany
- MPG, Germany
- Science Foundation Ireland (SFI), Ireland
- Department of Business, Enterprise and Innovation (DBEI), Ireland
- NWO, The Netherlands
- Science and Technology Facilities Council, UK
- Ministry of Science and Higher Education, Poland
- Istituto Nazionale di Astrofisica (INAF), Italy
- SURF Cooperative [180169]
- LOFAR e-infra group
- Gauss Centre for Supercomputing e.V. through the John von Neumann Institute for Computing (NIC) [CHTB00]
- STFC [ST/P000096/1]
- Deutsche Forschungsgemeinschaft under Germany's Excellence Strategy [EXC 2121, 05A20STA]
- UK Science and Technology Facilities Council [ST/R000905/1]
- VIDI research programme - Netherlands Organisation for Scientific Research (NWO) [639.042.729]
- Deutsche Forschungsgemeinschaft [EXC 2121, 390833306]
- German Science Foundation DFG, within the Collaborative Research Center [SFB1491]
- National Aeronautics and Space Administration
This study investigates the radio-star formation rate relationship in galaxies using low-frequency radio observations. The results show that more massive galaxies with higher star formation rates have stronger radio signals. The study also reveals variations in the radio spectral index, with steeper indices in galaxies with higher SFRs.
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.
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