A broad HCO+ absorption line associated with the circumnuclear torus of NGC 1052

Abstract

In the circumnuclear region of the nearby radio galaxy NGC~1052. Our $\lambda$3mm VLBI observations with the Korean VLBI Network have spatially resolved the broad HCO$^{+}$ absorption at a velocity range of 1350--1850 km~s$^{-1}$ against a double-sided nuclear jet, and have revealed that the HCO$^{+}$ absorption is concentrated on the receding jet and the nuclear components. The distribution of the HCO$^{+}$ absorbing gas strongly supports the circumnuclear torus surrounding the supermassive black hole. From the estimations of the column density and the volume density of molecular hydrogen, the size of the molecular gas region in the torus is at least 1~pc. The broad spectral profile of HCO$^{+}$ is likely to be a blend of multiple gas clumps with various velocities. The HCO$^{+}$ absorption of NGC~1052 could trace complex kinematics in the vicinity of the active galactic nucleus, such as inflow, outflow, turbulence, and so on.