The nuclear gas disk of NGC 1566 dissected by SINFONI and ALMA ^{⋆, ⋆⋆}

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: smajic@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Observatoire de Paris, LERMA, PSL, CNRS, Sorbonne Univ. UPMC and College de France, 75014 Paris, France
⁴ Observatorio Astronómico Nacional (OAN) – Observatorio de Madrid, Alfonso XII 3, 28014 Madrid, Spain

Received: 22 August 2014
Accepted: 10 August 2015

Abstract

We present the results of near-infrared (NIR) H- and K-band European Southern Observatory SINFONI integral field spectroscopy (IFS) 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 in north-south direction (PA ~ 5°). The galaxy inhibits a very active Seyfert 1 nucleus but narrow line ratios from optical observations in the nuclear region are similar to Seyfert 2 galaxies. The recent strong activity phase, as inferred from strong variablity in X-ray to IR wavelengths, makes NGC 1566 an ideal candidate to look for feeding and feedback of a supermassive black hole. We present emission and absorption line measurements in the central kpc of NGC 1566. Broad and narrow Brγ lines were detected. The detection of a broad Brγ component is a clear sign of a supermassive 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 [Fe ii] 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 H₂(1−0)S(1) and cold ¹²CO(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 H₂(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. Gas that might be shocked is detected ≈2″ from the center, which is visible in dispersion maps of H₂(1−0)S(1) and ¹²CO(3−2) and in the 0.87 mm continuum.