15-GHz radio emission from nearby low-luminosity active galactic nuclei^⋆

¹ Department of Astrophysics/IMAPP, Radboud University, Nijmegen, 6500, GL, The Netherlands
e-mail: p.saikia@astro.ru.nl
² New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE
³ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, Evanston, IL 60208, USA
⁴ Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA
⁵ Netherlands Institute for Radio Astronomy (ASTRON), AA Dwingeloo, PO Box 2, 7990, The Netherlands
⁶ Department of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
⁷ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK

Received: 14 April 2018
Accepted: 9 May 2018

Abstract

We present a sub-arcsec resolution radio imaging survey of a sample of 76 low-luminosity active galactic nuclei (LLAGN) that were previously not detected with the Very Large Array at 15 GHz. Compact, parsec-scale radio emission has been detected above a flux density of 40 μ Jy in 60% (45 of 76) of the LLAGN sample. We detect 20 out of 31 (64%) low-ionization nuclear emission-line region (LINER) nuclei, ten out of 14 (71%) low-luminosity Seyfert galaxies, and 15 out of 31 (48%) transition objects. We use this sample to explore correlations between different emission lines and the radio luminosity. We also populate the X-ray and the optical fundamental plane of black hole activity and further refine its parameters. We obtain a fundamental plane relation of log L_R = 0.48 (±0.04) log L_X + 0.79 (±0.03) log M and an optical fundamental plane relation of log L_R = 0.63 (±0.05) log L_{[O III]} + 0.67 (±0.03) log M after including all the LLAGN detected at high resolution at 15 GHz, and the best-studied hard-state X-ray binaries (luminosities are given in erg s⁻¹ while the masses are in units of solar mass). Finally, we find conclusive evidence that the nuclear 15 GHz radio luminosity function (RLF) of all the detected Palomar Sample LLAGN has a turnover at the low-luminosity end, and is best-fitted with a broken power law. The break in the power law occurs at a critical mass accretion rate of 1.2 × 10⁻³ M_⊙ yr⁻¹, which translates to an Eddington ratio of ṁ_Edd ~ 5.1 × 10⁻⁵, assuming a black hole mass of 10⁹ M_⊙. The local group stands closer to the extrapolation of the higher-luminosity sources, and the classical Seyferts agree with the nuclear RLF of the LLAGN in the local universe.