Chandra snapshot observations of low-luminosity active galactic nuclei with a compact radio source

The results of Chandra snapshot observations of 11 low-ionization nuclear emission-line regions (LINERs), three low-luminosity Seyfert galaxies, and one H II-LINER transition object are presented. Our sample consists of all the objects with a flat- or inverted-spectrum, compact radio core in the Very Large Array survey of 48 low-luminosity AGNs (LLAGNs) by Nagar and coworkers in 2000. An X-ray nucleus is detected in all galaxies except one, and their X-ray luminosities are in the range 5x10(38)-8x10(41) ergs s(-1). The X-ray spectra are generally steeper than expected from thermal bremsstrahlung emission from an advection-dominated accretion flow. The X-ray-to-Halpha luminosity ratios for 11 of 14 objects are in good agreement, with the value characteristic of LLAGNs and more luminous AGNs, and indicate that their optical emission lines are predominantly powered by an LLAGN. For three objects, this ratio is less than expected. Comparing with properties in other wavelengths, we find that these three galaxies are most likely to be heavily obscured AGNs. We use the ratio R-X=vL(v)(5 GHz)/L-X, where L-X is the luminosity in the 2-10 keV band, as a measure of radio loudness. In contrast to the usual definition of radio loudness [R-o=L-v(5 GHz)/L(B)], R-X can be used for heavily obscured (N(H)greater than or similar to10(23) cm(-2), A(V)>50 mag) nuclei. Further, with the high spatial resolution of Chandra, the nuclear X-ray emission of LLAGNs is often easier to measure than the nuclear optical emission. We investigate the values of R-X for LLAGNs, luminous Seyfert galaxies, quasars, and radio galaxies and confirm the suggestion that a large fraction of LLAGNs are radio-loud.