High-resolution radio continuum survey of M33 II. Thermal and nonthermal emission

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dc.creatorTabatabaei, F. S.
dc.creatorBeck, R.
dc.creatorKrügel, E.
dc.creatorKrause, M.
dc.creatorBerkhuijsen, E. M.
dc.creatorGordon, K. D.
dc.creatorMenten, K. M.
dc.date2007-08-20
dc.date.accessioned2026-07-07T08:34:14Z
dc.date.available2026-07-07T08:34:14Z
dc.descriptionWe determine the variation in the nonthermal radio spectral index in the nearby spiral galaxy M33 at a linear resolution of 360 pc. We separate the thermal and nonthermal components of the radio continuum emission without the assumption of a constant nonthermal spectral index. Using the Spitzer FIR data at 70 and 160 $μ$m and a standard dust model, we deredden the H$α$ emission. The extinction corrected H$α$ emission serves as a template for the thermal free-free radio emission. Subtracting from the observed 3.6 cm and 20 cm emission (Effelsberg and the VLA) this free-free emission, we obtain the nonthermal maps. A constant electron temperature used to obtain the thermal radio intensity seems appropriate for M~33 which, unlike the Milky Way, has a shallow metallicity gradient. For the first time, we derive the distribution of the nonthermal spectral index across a galaxy, M33. We detect strong nonthermal emission from the spiral arms and star-forming regions. Wavelet analysis shows that at 3.6 cm the nonthermal emission is dominated by contributions from star-forming regions, while it is smoothly distributed at 20 cm. For the whole galaxy, we obtain thermal fractions of 51% and 18% at 3.6 cm and 20 cm, respectively. The thermal emission is slightly stronger in the southern than in the northern half of the galaxy. We find a clear radial gradient of mean extinction in the galactic plane. The nonthermal spectral index map indicates that the relativistic electrons suffer energy-loss when diffusing from their origin in star-forming regions towards interarm regions and the outer parts of the galaxy. We also conclude that the radio emission is mostly nonthermal at R $>$ 5 kpc in M33.
dc.description15 pages, 14 figures, accepted for publication in the Astronomy and Astrophysics journal
dc.identifierhttps://arxiv.org/abs/0708.2484
dc.identifierhttp://arxiv.org/abs/0708.2484
dc.identifierdoi:10.1051/0004-6361:20078174
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/139362
dc.subjectAstrophysics
dc.titleHigh-resolution radio continuum survey of M33 II. Thermal and nonthermal emission
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