15 GHz compact structure in galactic nuclei

Abstract

We present 0″.2 resolution maps of 15 GHz continuum emission in 11 infrared and radio-bright galactic nuclei. The high angular resolution and short wavelength favor the detection of AGNs and other bright compact sources of flat spectral index. We divide the galaxies into three groups. In NGC 2992, NGC 3079, NGC 4151, and NGC 4388, the low-infrared luminosities, high radio-to-infrared luminosities, and small, bright (TB> 103K), centrally located radio sources, are most likely associated with AGNs. In NGC 520, NGC 660, NGC 2146, and NGC 3628, higher infrared luminosities, lower radio-to-infrared luminosity ratios, and multiple compact radio components that are less bright (TB< 300 K), are likely to be produced by star formation, probably in large part by compact H II regions. In the extremely luminous infrared galaxies NGC 6240 and NGC 3690, the high brightness temperatures (TB> 103K) of the radio components, together with their unusually high LIRand relatively low Brackett line fluxes, indicate that the compact knots may be associated with both AGN and star formation.