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

TL;DR

This study uses ALMA observations to analyze sulfur-bearing molecules in NGC 1052, revealing a warm molecular torus and cooler downstream flows, with jet-torus interaction causing shock heating and influencing jet collimation.

Contribution

It provides the first detailed measurement of sulfur-bearing molecule absorption features in NGC 1052, linking jet-torus interaction to shock heating and molecular gas properties.

Findings

High temperature (~344 K) in the torus indicates shock heating.

Sulfur-bearing molecules are released from dust via evaporation.

Jet-torus interaction influences jet collimation.

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 ALMA, we have measured the equivalent widths of SO absorption features in multiple transitions and determined the temperatures of $344 \pm 43$ K and $26 \pm 4$ K in sub-millimeter and millimeter wavelengths, respectively. Since sub-mm and mm continuum represents the core and jets, the high and low temperatures of the absorbers imply 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 gas phase released from dust. The origin of the sulfur-bearing gas is ascribed to evaporation of icy dust component through jet-torus interaction. Shock heating is the sole plausible mechanism to maintain such high temperature of gas and dust in the torus. Implication of jet-torus interaction also supports collimation of the sub-relativistic jets by gas pressure of the torus.