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| Paper IPM / Astronomy / 17944 |
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| Abstract: | |||||||||||||||||||
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Resolved studies of the correlation between the radio and far-infrared (FIR) emission from galaxies at different frequencies can unveil
the interplay between star formation and relativistic interstellar medium (ISM). Thanks to the LOFAR LoTSS observations combined
with the VLA, Herschel, and WISE data, we study the role of the cosmic rays and magnetic fields in the radio�â??FIR correlation on
scales of �â?�ó200 pc in the nearby galaxy IC342. The thermal emission traced by the 22 �?�õm emission, constitutes about 6%, 13%,
and 30% of the observed radio emission at 0.14, 1.4, 4.8 GHz, respectively, in star forming regions and less in other parts. The
nonthermal spectral index becomes flatter at frequencies lower than 1.4 GHz (�?�ñn= �â??0.51 �?�ñ 0.09, S �?�ý �â?ïÿý �?�ý
�?�ñn
) than between 1.4 and
4.8 GHz (�?�ñn= �â??1.06 �?�ñ 0.19) on average and this flattening occurs not only in star-forming regions but also in diffuse ISM. The radio�â??
FIR correlation holds at all radio frequencies; however, it is tighter at higher radio frequencies. A multi-scale analysis shows that this
correlation cannot be maintained on small scales due to diffusion of cosmic ray electrons (CREs). The correlation breaks on a larger
scale (�â??320 pc) at 0.14 GHz than at 1.4 GHz (�â??200 pc) indicating that those CREs traced at lower frequencies have diffused a longer
path in the ISM. We find that the energy index of CREs becomes flatter in star forming regions in agreement with previous studies.
Cooling of CREs due to the magnetic field is evident globally only after compensating for the effect of star formation activity which
both accelerate CREs and amplify magnetic fields. Compared with other nearby galaxies, it is shown that the smallest scale of the
radio�â??FIR correlation is proportional to the CREs propagation length on which the ordered magnetic field has an important effect
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