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2.6. Compact Radio Cores

Finally, further verisimilitude with the AGN phenomenon can be sought by means of high-resolution radio continuum observations. As already mentioned above, compact, flat-spectrum cores of low power are often found in radio continuum surveys of nearby elliptical and S0 galaxies. Less certain is the incidence of the similar phenomenon in spirals, which in general tend to be rather weak radio sources. A large subsample of LINERs from the Palomar survey is being systematically mapped at 2, 3.6, and 6 cm using the the Very Large Array in its most extended configuration. The highest angular resolution achieved is comparable to that of HST, and faint, sub-mJy compact sources can be routinely detected with ease. The preliminary analysis, reported in Van Dyk and Ho (1997), finds that the 6 cm maps nearly always detect a single, compact core spatially coincident with the optical nucleus. Most of the radio cores have relatively steep spectral indices consistent with optically thin synchrotron emission, but a significant fraction has flat, presumably optically thick, spectra (Falcke et al. 1997).