Constraints on the Mass Accretion Rate onto the Supermassive Black Hole of Cygnus A Using the Submillimeter Array

We present the first detailed polarimetric studies of Cygnus A at 230 GHz with the Submillimeter Array (SMA) to constrain the mass accretion rate onto its supermassive black hole. We detected the polarized emission associated with the core at a fractional polarization of 0.73 +/- 0.15%. This low fractional polarization suggests that the polarized emission is highly depolarized. One of the possible explanations is due to a significant variance in the Faraday rotation measure within the synthesized beam. By assuming the Faraday depolarization caused by inhomogeneous column density of the magnetized plasma associated with the surrounding radiatively-inefficient accretion flow within the SMA beam, we derived the constraint on the mass accretion rate to be larger than 0.15 M-circle dot yr(-1) at the Bondi radius. The derived constraint indicates that an adiabatic inflow-outflow solution or an advection-dominated accretion flow should be preferable as the accretion flow model in order to explain the jet power of Cygnus A.

Automated summary

Polarimetric studies of Cygnus A at 230 GHz using the Submillimeter Array provided constraints on the mass accretion rate onto its supermassive black hole. The low fractional polarization of the detected emission suggests high depolarization, potentially due to significant variance in Faraday rotation measure. The derived constraint indicates the need for an adiabatic inflow-outflow solution or advection-dominated accretion flow model to explain the jet power of Cygnus A.