H_2O maser and a plasma obscuring torus in the radio galaxy NGC 1052

TL;DR

This study uses multi-frequency VLBA observations to analyze the jet structure and H_2O maser emission in NGC 1052, revealing a plasma-obscured torus and insights into the galaxy's nuclear environment.

Contribution

It provides the first detailed multi-frequency imaging of NGC 1052's jets and masers, suggesting the presence of a circumnuclear torus associated with the maser emission.

Findings

Detection of redshifted H_2O masers aligned with the jets.

Identification of free-free absorption indicating a plasma torus.

Jet orientation close to the sky plane.

Abstract

We present multi-frequency simultaneous VLBA observations at 15, 22 and 43 GHz towards the nucleus of the nearby radio galaxy NGC 1052. These three continuum images reveal a double-sided jet structure, whose relative intensity ratios imply that the jet axis is oriented close to the sky plane. The steeply rising spectra at 15-43 GHz at the inner edges of the jets strongly suggest that synchrotron emission is absorbed by foreground thermal plasma. We detected H_2O maser emission in the velocity range of 1550-1850 km/s, which is redshifted by 50-350 km/s with respect to the systemic velocity of NGC 1052. The redshifted maser gas appears projected against both sides of the jet, similar to the HI seen in absorption. The H_2O maser gas is located where the free-free absorption opacity is large. This probably implies that the masers in NGC 1052 are associated with a circumnuclear torus or disk as in the nucleus of NGC 4258. Such circumnuclear structure can be the sense of accreting onto the central engine.