A fundamental plane of black hole accretion at millimetre wavelengths

Abstract

We report the discovery of the 'mm fundamental plane of black hole accretion', which is a tight correlation between the nuclear 1 mm luminosity (L<SUB>ν, mm</SUB>), the intrinsic 2-10 keV X-ray luminosity (L<SUB>X, 2-10</SUB>) and the supermassive black hole (SMBH) mass (M<SUB>BH</SUB>) with an intrinsic scatter (σ<SUB>int</SUB>) of 0.40 dex. The plane is found for a sample of 48 nearby galaxies, most of which are low-luminosity active galactic nuclei. Combining these sources with a sample of high-luminosity (quasar-like) nearby AGN, we show that the plane still holds. We also find that M<SUB>BH</SUB> correlates with L<SUB>ν, mm</SUB> at a highly significant level, although such correlation is less tight than the mm fundamental plane (σ<SUB>int</SUB> = 0.51 dex). Crucially, we show that spectral energy distribution (SED) models for both advection-dominated accretion flows (ADAFs) and compact jets can explain the existence of these relations, which are not reproduced by the standard torus-thin accretion disc models usually associated to quasar-like AGN. The ADAF models reproduces the observed relations somewhat better than those for compact jets, although neither provides a perfect fit. Our findings thus suggest that radiatively inefficient accretion processes such as those in ADAFs or compact (and thus possibly young) jets may play a key role in both low- and high-luminosity AGN. This mm fundamental plane also offers a new, rapid method to (indirectly) estimate SMBH masses.