Mathematics – Logic
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...18912207g&link_type=abstract
American Astronomical Society, 189th AAS Meeting, late abstracts, #122.07; Bulletin of the American Astronomical, Vol. 29, p. 73
Mathematics
Logic
Scientific paper
We present high resolution radio continuum observations of the edge-on galaxy NGC4631 with the Very Large Array A & B arrays in the L--, C--, and X--band. The emission on the scales we observed is limited to the inner rigidly rotating and star forming 4kpc diameter disk of NGC4631. Point sources are identified at resolutions of 1.45'' and 0.83'' x 0.61'' in this region, and their flux densities and spectral indices are derived. Most of the emission, including the ~ 20 point sources, has a flat thermal spectrum. This can be understood in terms of missing large-scale emission of the interferometric observations, and the fact that non-thermal radio emission has a more extended and diffuse distribution than the thermal emission. The flux density of the observed presumably thermal emission is consistent with a star formation rate derived from FIR observations if we assume that about 50% of the FIR emission comes from dust heated by the general interstellar radiation field. Independent evidence for this latter assumption can be derived from radio spectral index studies. The two brightest non-thermal source complexes in NGC4631 show strong morphological evidence for being external to NGC4631; they are likely radio galaxies in the background. Alternatively, we discuss whether one of these sources may be the weakly active nucleus with jet--like features. Only three other point sources are probably non--thermal and may be indentified with supernova remnants. Using CAS A as a standard `candle', we estimate a supernova rate from this and show that the rate is inconsistent with the star formation rate by a factor of at least ~ 6. Implications of this discrepancy are discussed.
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