Publication Date:
2013-07-26
Description:
We present the first maps of NGC 3044 and NGC 4157 at 450 μm and 850 μm from the James Clerk Maxwell Telescope as well as the first maps at 617 MHz 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 617 MHz 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 10 kpc from the major axis, has apparently associated emission at 20 cm 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 ( T c = 9.5 K for NGC 3044 and T c = 15.3 K for NGC 4157). Dust masses are M d = 1.6 x 10 8 M and M d = 2.1 x 10 7 M for NGC 3044 and NGC 4157, respectively, and are dominated by the cold component. There is a clear correlation between the 617 MHz and 850 μm emission in the two galaxies. In the case of NGC 3044 for which the 850 μm data are strongly dominated by cold dust, this implies a relation between the non-thermal synchrotron emission and cold dust. The 617 MHz component represents an integration of massive star formation over the past 10 7–8 yr and the 850 μm emission represents heating from the diffuse interstellar radiation field (ISRF). The 617 MHz– 850 μm correlation improves when a smoothing kernel is applied to the 850 μm 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 $L_{617_{\rm MHz}}\,\propto \,{L_{850\mu {\rm m}}}^{2.1\,\pm \,0.2}$ 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 $L_{617_{\rm MHz}}\,\propto \,{L_{850\mu {\rm m}}}^{2.2}$ , in agreement with the observed correlation.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
Permalink
