Ionized regions in the central arcsecond of NGC 1068. YJHK spatially resolved spectroscopy

TL;DR

This study uses spatially resolved spectroscopy to analyze ionized regions near the nucleus of NGC 1068, revealing that shock processes from jet-cloud interactions dominate the ionization over photoionization.

Contribution

It provides the first detailed spectral analysis of multiple regions in NGC 1068, demonstrating the dominance of shock ionization in the central arcsecond.

Findings

Shock models best fit the emission spectra.

Regions are similar, indicating a common origin.

Multiple ionization phases with high temperatures.

Abstract

Context. Several bright emission line regions have been observed in the central 100 parsecs of the active galaxy NGC 1068. Aims. We aim to determine the properties and ionization mechanism of three regions of NGC 1068: the nucleus (B) and two clouds located at 0.3" and 0.7" north of it (C and D). Methods. We combined SPHERE (0.95 - 1.65 um) and SINFONI (1.5 - 2.45 um) spectra for the three regions B, C, and D. We compared these spectra to several CLOUDY photoionization models and to the MAPPINGS III Library of Fast Radiative Shock Models. Results. The emission line spectra of the three regions are almost identical to each other and contribute to most of the emission line flux in the nuclear region. The emitting media contain multiple phases, the most luminous of which have temperatures ranging from 104.8 K to 106 K. Central photoionization models can reproduce some features of the spectra, but the fast radiative shock model provides the best fit to the data. Conclusions. The similarity between the three regions indicates that they belong to the same class of objects. Based on our comparisons, we conclude that they are shock regions located where the jet of the active galactic nucleus impacts massive molecular clouds.