The nuclear gas disk of NGC 1566 dissected by SINFONI and ALMA

TL;DR

This study uses integral field spectroscopy to analyze the nuclear gas disk of NGC 1566, revealing a rotating molecular gas disk, signs of an active galactic nucleus, and a nuclear spiral facilitating gas inflow to the center.

Contribution

First detailed multi-wavelength analysis of NGC 1566's nuclear gas disk combining SINFONI and ALMA data, highlighting the gas dynamics and excitation conditions near the supermassive black hole.

Findings

Detection of a supermassive black hole via broad Brγ lines.

Identification of a nuclear gas disk with a radius of about 3 arcseconds.

Evidence of a nuclear spiral structure aiding gas inflow.

Abstract

We present the results of near-infrared H- and K-band European Southern Observatory SINFONI integral field spectroscopy of the Seyfert galaxy NGC 1566. We investigate the central kpc of this nearby galaxy, concentrating on excitation conditions, morphology, and stellar content. NGC 1566 was selected from our NUGA (-south) sample and is a ringed, spiral galaxy with a stellar bar. We present emission and absorption line measurements in the central kpc of NGC 1566. Broad and narrow Br{\gamma} lines were detected. The detection of a broad Br{\gamma} component is a clear sign of a super-massive black hole in the center. Blackbody emission temperatures of ~1000 K are indicative of a hot dust component, the torus, in the nuclear region. The molecular hydrogen lines, hydrogen recombination lines, and [FeII] indicate that the excitation at the center is coming from an AGN. The central region is predominantly inhabited by molecular gas, dust, and an old K-M type giant stellar population. The molecular gas and stellar velocity maps both show a rotation pattern. The molecular gas velocity field shows a perturbation toward the center that is typical for bars or spiral density waves. The molecular gas species of warm H_2(1-0)S(1) and cold ^{12}CO(3-2) gas trace a nuclear gas disk of about 3" in radius with a nuclear spiral reaching toward the nucleus. From the equivalent width of H_2(1-0)S(1) a molecular ring with r<~3" can be inferred. This spiral seems to be an instrument that allows gas to fall toward the nucleus down to <50 pc scales. The excitation of molecular hydrogen in the nuclear gas disk is not clear but diagnostic diagrams show a distinction between the nuclear region and a <9 Myr old star forming region at the southwestern spiral arm. Possibly shocked gas is detected ~2" from the center, which is visible in dispersion maps of H$_2$(1-0)S(1) and ^{12}CO(3-2) and in the 0.87 mm continuum.