Nuclear and Extended Spectra of NGC 1068 - I: Hints from Near-Infrared Spectroscopy

TL;DR

This study presents the first simultaneous near-infrared spectra of NGC 1068, revealing complex emission line structures, dust contributions, and stellar populations, advancing understanding of the galaxy's nuclear environment.

Contribution

It provides new high-resolution, multi-component spectral data of NGC 1068's nucleus, including insights into ionization mechanisms, stellar populations, and mass distribution.

Findings

Detection of split low-ionization lines correlated with jets

Presence of single-peaked coronal lines near the nucleus

Identification of intermediate-age stellar populations contributing to NIR continuum

Abstract

We report the first simultaneous zJHK spectroscopy on the archetypical Seyfert 2 Galaxy NGC 1068 covering the wavelength region 0.9 to 2.4 micron. The slit, aligned in the NS direction and centred in the optical nucleus, maps a region 300 pc in radius at sub-arcsec resolution, with a spectral resolving power of 360 km s^-1. This configuration allow us to study the physical properties of the nuclear gas including that of the north side of the ionization cone, map the strong excess of continuum emission in the K-band and attributed to dust and study the variations, both in flux and profile, in the emission lines. Our results show that (1) Mid- to low-ionization emission lines are splitted into two components, whose relative strengths vary with the position along the slit and seem to be correlated with the jet. (2) The coronal lines are single-peaked and are detected only in the central few hundred of parsecs from the nucleus. (3) The absorption lines indicate the presence of intermediate age stellar population, which might be a significant contributor to the continuum in the NIR spectra. (4) Through some simple photoionization models we find photoionization as the main mechanism powering the emitting gas. (5) Calculations using stellar features point to a mass concentration inside the 100 - 200 pc of about 10^10 solar masses.