High Sensitivity Observations of the Water Megamasers of NGC 1068: Precise Astrometry and Detailed Kinematics

TL;DR

This study uses high sensitivity radio observations to map water megamasers in NGC 1068, revealing detailed disk structure, kinematics, magnetic fields, and jet interactions, advancing understanding of active galactic nuclei.

Contribution

It provides the first precise astrometry and detailed kinematic analysis of NGC 1068's water megamasers, including detection of spiral structures and magnetic fields.

Findings

Disk masers are associated with the nuclear radio source S1.

Disk exhibits Keplerian rotation with a central mass of 17 million solar masses.

Magnetic fields in the disk are stronger than 1.6 mG, influencing maser structures.

Abstract

We present High Sensitivity Array observation of the water megamasers of NGC 1068. We obtain absolute astrometry with 0.3 mas precision that confirms the association of the disk masers with the nuclear radio continuum source S1. The new observations reveal two new blueshifted groups of disk masers. We also detect the 22 GHz continuum on short interferometric baselines. The position-velocity diagram of the disk masers shows a curve consistent with a nonaxisymmetric distribution of maser spots. The curve is probably the result of spiral arms with a constant pitch angle of roughly 5 degrees. The disk kinematics are consistent with Keplerian rotation and low turbulent speeds. The inferred central mass is 17 million solar masses. On the basis of disk stability arguments, the mass of the molecular disk is roughly 110 thousand solar masses. The disk masers further resolve into filamentary structures suggesting an ordered magnetic field threading the maser disk. The magnetic field strengths must be greater than 1.6 mG to withstand turbulent motions in the partially ionized molecular gas. We note apparent asymmetries in the molecular disk that might be explained by anisotropic heating by a misaligned inner accretion disk. The new observations also detect the fainter jet masers north of the disk masers. The distribution and kinematics of the jet masers are consistent with an expanding ring of molecular gas.