NGC 1566: analysis of the nuclear region from optical and near-infrared Integral Field Unit spectroscopy

TL;DR

This study uses optical and near-infrared integral field spectroscopy to analyze the nuclear region of NGC 1566, revealing details about its active nucleus, emission features, and surrounding structures, supporting the unified model of AGN.

Contribution

It applies advanced spectral analysis techniques to characterize the AGN and its environment in NGC 1566, providing new insights into the structure and dynamics of the nuclear region.

Findings

The AGN exhibits Seyfert 1 emission with a strong featureless continuum.

Detected a correlation between redshift and BLR line width, modeled as gravitational redshift.

Identified a rotating H2 disc and an outflow, supporting the unified AGN model.

Abstract

We analysed the centre of NGC 1566, which hosts a well-studied active galactic nucleus (AGN), known for its variability. With the aid of techniques such as Principal Component Analysis Tomography, analysis of the emission-line spectra, channel maps, Penalized Pixel Fitting and spectral synthesis applied to the optical and near-infrared data cubes, besides the analysis of Hubble Space Telescope images, we found that: (1) the AGN has a Seyfert 1 emission, with a very strong featureless continuum that we described as a power law with spectral index of 1.7. However, this emission may come not only from the AGN [as its point spread function (PSF) is broader than the PSF of the broad-line region (BLR)], but from hot and young stars, the same ones that probably account for the observed sigma-drop. (2) There is a correlation between redshift and the full width at half-maximum of the BLR emission lines. With a simple model assuming gravitational redshift, we described it as an emitting ring with varying emitting radii and small inclination angles. (3) There is an H II region close to the AGN, which is composed of many substructures forming an apparent spiral with a velocity gradient. (4) We also detected a probable outflow coming from the AGN and it seems to contaminate the H II region emission. (5) We identified an H2 rotating disc with orientation approximately perpendicular to this outflow. This suggests that the rotating disc is an extension of an inner torus/disc structure, which collimates the outflow emission, according to the Unified Model.