Probing the Jet–Torus Interaction in the Radio Galaxy NGC 1052 by Sulfur-bearing Molecules

Abstract

The radio galaxy NGC 1052 casts absorption features of sulfur-bearing molecules, H _2 S, SO, SO _2 , and CS toward the radio continuum emission from the core and jets. Using the Atacama Large Millimeter/submillimeter Array, we have measured the equivalent widths of SO absorption features in multiple transitions and determined the temperatures of 344 ± 43 K and 26 ± 4 K in submillimeter and millimeter wavelengths, respectively. Since submillimeter and millimeter continuum represents the core and jets, the high and low temperatures of the absorbers imply a warm environment in the molecular torus and cooler downstream flows. The high temperature in the torus is consistent with the presence of 22 GHz H _2 O maser emission, vibrationally excited HCN and HCO ^+ absorption lines, and sulfur-bearing molecules in the gas phase released from dust. The origin of the sulfur-bearing gas is ascribed to the evaporation of the icy dust component through a jet–torus interaction. Shock heating is the sole plausible mechanism to maintain such a high temperature of gas and dust in the torus. The implication of the jet–torus interaction also supports the collimation of the sub-relativistic jets by the gas pressure of the torus.

Keywords

• Active galactic nuclei
• Molecular spectroscopy
• Radio galaxies
• Radio jets