2013MNRAS.433.2958I

We present the first maps of NGC 3044 and NGC 4157 at λ450µm and λ850µm from the James Clerk Maxwell Telescope as well as the first maps at 617MHz from the Giant Metrewave Radio Telescope. High-latitude emission has been detected in both the radio continuum and sub-mm for NGC 3044 and in the radio continuum for NGC 4157, including several new features. For NGC 3044, in addition, we find 617MHz emission extending to the north of the major axis, beginning at the far ends of the major axis. One of these low-intensity features, more than 10kpc from the major axis, has apparently associated emission at λ20cm and may be a result of in-disc activity related to star formation.

The dust spectrum at long wavelengths required fitting with a two-temperature model for both galaxies, implying the presence of cold dust (Tc=9.5K for NGC 3044 and Tc=15.3K for NGC 4157). Dust masses are Md=1.6x108M☉ and Md=2.1x107M☉ for NGC 3044 and NGC 4157, respectively, and are dominated by the cold component.

There is a clear correlation between the 617MHz and λ850µm emission in the two galaxies. In the case of NGC 3044 for which the λ850µm data are strongly dominated by cold dust, this implies a relation between the non-thermal synchrotron emission and cold dust. The 617MHz component represents an integration of massive star formation over the past 107-8yr and the λ850µm emission represents heating from the diffuse interstellar radiation field (ISRF).

The 617MHz-λ850µm correlation improves when a smoothing kernel is applied to the λ850µm data to account for differences between the cosmic ray (CR) electron diffusion scale and the mean free path of an ISRF photon to dust. The best-fitting relation is L_617_MHz ∝ L_850µm^2.1 ± 0.2 for NGC 3044. If variations in the cold dust emissivity are dominated by variations in dust density, and the synchrotron emission depends on magnetic field strength (a function of gas density) as well as CR electron generation (a function of massive star formation rate and therefore density via the Schmidt law) then the expected correlation for NGC 3044 is L_617_MHz ∝ L_850µm^2.2, in agreement with the observed correlation.