1,171 research outputs found
The radio-infrared correlation in galaxies
The radio-infrared correlation was explained as a direct and linear
relationship between star formation and IR emission. However, one fact making
the IR-star formation linkage less obvious is that the IR emission consists of
at least two emission components, cold dust and warm dust. The cold dust
emission may not be directly linked to the young stellar population.
Furthermore, understanding the origin of the radio-IR correlation requires to
discriminate between the two main components of the radio continuum emission,
free-free and synchrotron emission. Here, we present a multi-scale study of the
correlation of IR with both the thermal and non-thermal (synchrotron)
components of the radio continuum emission from the nearby galaxies M33 and
M31.Comment: To appear in Highlights of Astronomy, Volume 15, XXVIIth IAU General
Assembly, August 200
Radio emission during the formation of stellar clusters in M33
We investigate thermal and non-thermal radio continuum associated with the
early formation and evolution of Young Stellar Clusters (YSCs) selected by
their MIR emission in M33. For the first time in an external galaxy it has been
possible to identify radio counterparts to more than 300 star forming regions.
We proof the nature of candidate YSCs fully embedded in molecular clouds, by
recovering their associated faint radio continuum luminosities. Using the
Halpha line to identify free-free radio emission at 5 GHz in the more evolved,
partially exposed YSCs, we retrieve information on the relevance of magnetic
fields and cosmic rays across the M33 disk at 25 pc spatial scales. A
cross-correlation of MIR and radio continuum luminosities is established from
bright to very faint YSCs, with MIR-to-radio emission ratio showing a gradual
decline towards the outer disk, while the magnetic field is pervasive at all
radii. We establish and discuss the tight relation between radio continuum and
other star formation indicators, such as Halpha. This relation holds for
individual YSCs over four orders of magnitude as well as for molecular clouds
hosting YSCs. On average about half of radio emission at 5 GHz in YSCs is
non-thermal. For exposed but compact YSCs the non-thermal radio fraction
increases with source brightness, while for large HII regions the fraction is
lower and shows no clear trend. This has been found for YSCs with and without
identified SNRs and underlines the possible role of massive stars in triggering
particle acceleration through winds and shocks: these particles diffuse
throughout the native molecular cloud prior to cloud dispersal.Comment: 14 pages, 10 figures, accepted for publication in A&
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