Dwarf Galaxies: From the Deep Universe to the Present Proceedings IAU Symposium No. 344, 2019 K. B. W. McQuinn & S. Stierwalt, eds. c  International Astronomical Union 2019 doi:10.1017/S1743921318006841 Stellar feedback in dwarf irregular galaxies with radio continuum observations Volker Heesen 1 , Aritra Basu 2 , Elias Brinks 3 , George Heald 4 , Andrew Fletcher 5 , Cathy Horellou 6 , Matthias Hoeft 7 and Krzysztof Chy˙ zy 8 1 Hamburger Sternwarte, Universit¨at Hamburg, Gojenbergsweg 112, 21029 Hamburg email: volker.heesen@hs.uni-hamburg.de 2 Fakult¨ at f¨ ur Physik, Universit¨ at Bielefeld, Postfach 100131, D-33501 Bielefeld, Germany 3 University of Hertfordshire, Hatfield AL10 9AB, UK 4 CSIRO, 26 Dick Perry Avenue, Kensington, WA 6151, Australia 5 Newcastle University, Newcastle-upon-Tyne NE1 7RU, UK 6 Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden 7 Th¨ uringer Landessternwarte (TLS), Sternwarte 5, D-07778 Tautenburg, Germany 8 Astronomical Observatory, Jagiellonian University, ul. Orla 171, PL-30-244 Krak´ow, Poland Abstract. Low-mass dwarf irregular galaxies are subject to outflows, in which cosmic rays may play a very important role; they can be traced via their electron component, the cosmic ray electrons (CRe), in the radio continuum as non-thermal synchrotron emission. With the advent of sensitive low-frequency observations, such as with the Low-Frequency Array (LOFAR), we can trace CRe far away from star formation sites. Together with GHz-observations, such as with the Very Large Array (VLA), we can study spatially resolved radio continuum spectra at matched angular resolution and sensitivity. Here, we present results from our 6-GHz VLA survey of 40 nearby dwarf galaxies and our LOFAR study of the nearby starburst dwarf irregular galaxy IC 10. We explore the relation of RC emission with star formation tracers and study in IC 10 the nature of a low-frequency radio halo, which we find to be the result of a galactic wind. Keywords. cosmic rays, galaxies: magnetic fields, radio continuum: galaxies 1. Introduction Radio continuum (RC) emission in galaxies holds the potential to be an extinction- free star-formation tracer, which is accessible with ground-based observations. This is supported not only by the well known correlation between RC and far-infrared (FIR) emission (e.g. Yun, Reddy & Condon 2001), but also by relations to other star-formation tracers such as far-UV (FUV) and mid-infrared (MIR) emission (Heesen et al. 2014; Tabatabaei et al. 2017). The correlation is tight, with a scatter of only 0.2 dex (50 per cent) for integrated quantities, and holds locally at 1-kpc scale, although with a larger scatter. Given the complex physics of RC emission in galaxies, the mere existence of a relation between RC luminosity and star-formation rate (SFR) is remarkable. Dwarf galaxies, with their episodic star formation, low metallicities and thus poten- tially varying initial mass function, and their proneness to outflows offer a stringent test of the RC–SFR relation. Dwarf galaxies fall on the RC–FIR correlation (Bell 2003), which has been explained by ‘conspiracy’ between escape of dust-heating UV-photons and cos- mic ray electrons (CRe); at a typical frequency of 6 GHz the latter are responsible via synchrotron emission for approximately half of the RC emission, the remainder coming from thermal free–free emission. In this brief contribution, we present a summary of our 255 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921318006841 Downloaded from https://www.cambridge.org/core. IP address: 35.175.192.15, on 15 Oct 2021 at 08:35:06, subject to the Cambridge Core terms of use, available at