Radio Sources in Low - Luminosity Active Galactic Nuclei . I . VLA Detections ofCompact , Flat - Spectrum

We report a high resolution (0: 00 2), 15 GHz survey of a sample of 48 low-luminosity active galactic nuclei with the Very Large Array 1. Compact radio emission has been detected above a ux density of 1.1 mJy in 57% (17 of 30) of low-ionization nuclear emission-line region (LINER) nuclei and low-luminosity Seyferts. The 2 cm radio power is signiicantly correlated with the emission-line ((O I] 6300) luminosity. Using radio uxes at other frequencies from the literature, we nd that at least 15 of the 18 detected radio cores have a at to inverted spectrum (?0.3, S /). While the present observations are consistent with the radio emission originating in star forming regions (the brightness temperatures are 10 2:5?4:5 K), higher resolution radio observations of 10 of the detected sources, reported in a companion paper (Falcke et al. 2000), show that the cores are very compact (. pc), of high brightness temperature (T b & 10 8 K) and probably synchrotron self-absorbed, ruling out a starburst origin. Thus, our results suggest that at least 50% of low-luminosity Seyferts and LINERs in the sample are accretion powered, with the radio emission presumably coming from jets or advection-dominated accretion ows. We have detected only 1 of 18 \transition" (i.e. LINER + H II) nuclei observed, indicating their radio cores are signiicantly weaker than those of \pure" LINERs. Compact 2 cm radio cores are found in both type 1 (i.e. with broad H) and type 2 (without broad H) nuclei. There is weak evidence, limited in signiicance by small numbers, that low-luminosity active galactic nuclei with compact radio cores exhibit radio ejecta preferentially aligned along the rotation axis of the galaxy disk. If this result is connrmed by a larger sample, it would lend support to the idea that the misalignment of accretion disks with the galaxy stellar disk in more luminous Seyfert galaxies is a result of radiation-pressure induced warping of their accretion disks.