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Paper: Unveiling hidden AGNs in ULIRGs and low-luminosity AGN through high-frequency radio observations
Volume: 290, Active Galactic Nuclei: from Central Engine to Host Galaxy
Page: 397
Authors: Nagar, N. M.; Falcke, H.; Wilson, A. S.
Abstract: A compact (sub-parsec), high (> 108 K) brightness temperature radio core is a reliable indicator for the presence of an accreting massive black hole in a galaxy nucleus. Detecting such cores is facilitated by the absence of significant obscuration at high gigahertz frequencies (as compared to the UV to IR), and the availability of sensitive radio telescopes delivering the required resolution. Our high frequency high-resolution radio survey of all (∼200) low-luminosity active galactic nuclei (AGNs) from the Palomar sample of ∼500 nearby bright galaxies has found high brightness-temperature compact radio cores in almost half of all LINERs and low-luminosity Seyferts. The radio core properties (morphologies, luminosities and spectral shapes) provide strong evidence for the presence of accreting massive black holes in a large fraction, perhaps all, of LLAGNs, with the nuclear radio emission originating in either the accretion inflow onto the massive black hole or from jets launched by this black hole - accretion disk system. Current data favor the latter interpretation. We are now conducting a similar investigation on a complete sample of 118 ultraluminous infra-red galaxies (ULIRGs). High resolution radio data have now been obtained, and will be used to determine the incidence and evolution of AGN activity, and the interplay between AGN and star-formation activity in ULIRGs. A comparison between ULIRGs at different merging stages, and with our similar observations of (isolated) low-luminosity AGNs will be used to test the effect of mergers on AGN activity. Results of both studies above will be presented, and discussed in the context of black hole growth through merging and accretion.
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