Spatially Extended [P II]1.188um and [Fe II]1.257um Emission Lines in a Nearby Seyfert Galaxy NGC 1068 Observed with OAO/ISLE

TL;DR

This study uses J-band spectroscopy to analyze spatially extended [Fe II] and [P II] emission lines in NGC 1068, revealing variations in ionization mechanisms from photoionization near the nucleus to shock ionization further out.

Contribution

First spatially resolved J-band spectroscopic observations of [Fe II] and [P II] lines in NGC 1068, showing how ionization mechanisms change with distance from the nucleus.

Findings

Line ratio increases with distance from the nucleus.

Ratios near the nucleus match photoionization models.

Higher ratios at 3-4 arcseconds suggest shock ionization.

Abstract

We present J-band long-slit spectroscopic observation of NGC 1068 classified as a Seyfert 2 galaxy. J-band observations with OAO/ISLE provide clear detection of spatially extended [Fe II]1.257um and [P II]1.188um lines. We found that [Fe II]1.257um/[P II]1.188um increases with distance from a central continuum peak. Observed line ratios around the nucleus (continuum peak) are consistent with a typical value expected from photoionization models, while the ratios at 3" - 4" (210-280 pc) east and west of the nucleus are slightly higher than this. In the off nucleus region of NGC 1068 we also found a possible association between [Fe II]1.257um/[P II]1.188um and the radio continuum. This suggests a mild contribution of shock ionization induced by a radio jet outside nucleus while photoionization by the central energy source is dominant near the nucleus.