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S.G. Neff (NASA/GSFC), S.D. Campion (SSAI), J.S. Ulvestad (NRAO)
We present new 6cm and 4cm radio continuum images of the central regions of the merging galaxy systems NGC3256 and NGC4194. NGC3256 is imaged with a resolution of ~1\arcsec\ or ~190pc; NGC4194 is imaged with a resolution of ~0.3\arcsec\ or ~50pc. In both systems, we detect numerous compact radio sources embedded in more diffuse radio emission. We detect 65 compact sources in NGC3256 at 6cm and we detect 46 compact sources in NGC4194, both to a limiting luminosity of ~5 \times 1018 W Hz-1 or ~5 times the luminosity of Cas A. Most of the compact radio sources are loosely associated with active starforming regions but not with specific optical emission sources. Several compact radio sources in NGC3256 are near positions of compact X-ray sources detected by Lira et al. (2000).
In both NGC3256 and NGC4194, we are able to measure reliable spectral indices for the stronger sources. We find in NGC3256 ~20% have nominally flat radio spectral indices (indicating they are dominated by thermal radio emission from HII regions) while ~80% have nominally steep spectral indices (indicating they are dominated by nonthermal emission from supernova remnants). In NGC4194, half the compact radio sources have flat spectral indices and half have steep indices. For the flat-spectrum sources, we estimate the number of young massive stars and the associated ionized gas masses. For the steep-spectrum sources, we estimate supernova rates. We compare these results with those from other well-studied merging galaxy systems.
We gratefully acknowledge use of the NRAO Very Large Array (VLA) and the VLA Archive. NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.