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Testing black hole jet scaling relations in low-luminosity active galactic nuclei




We present the results of the analysis of a sample of 17 low-luminosity (LX≲ 1042 erg s−1), radio-loud active galactic nuclei in massive galaxies. The sample is extracted from the Sloan Digital Sky Survey data base and it spans uniformly a wide range in optical [O iii] emission line and radio luminosity, but within a narrow redshift range (0.05 < z < 0.11) and a narrow supermassive black hole mass range (∼108 M). For these sources we measured core X-ray emission with the Chandra X-ray Telescope and radio emission with the Very Large Array. Our main goal is to establish which emission component, if any, can be regarded as the most reliable accretion/jet-power estimator at these regimes. In order to do so, we studied the correlation between emission-line properties, radio luminosity, radio spectral slopes and X-ray luminosity, as well as more complex multivariate relations involving black hole mass, such as the Fundamental Plane of black hole activity. We find that 15 out of 17 sources of our sample can be classified as low-excitation galaxies (LEGs), and their observed properties suggest X-ray and radio emission to originate from the jet basis. We also find that X-ray emission does not appear to be affected by nuclear obscuration and can be used as a reliable jet-power estimator. More generally, X-ray, radio and optical emission appear to be related, although no tight correlation is found. In accordance with a number of recent studies of this class of objects, these findings may be explained by a lack of cold (molecular) gaseous structures in the innermost region of these massive galaxies.

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