Star formation and gas flows in the centre of the NUGA galaxy NGC 1808 observed with SINFONI^⋆

¹ I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: busch@ph1.uni-koeln.de; eckart@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Gemini Observatory, Northern Operations Center, 670 N. A’ohoku Place, Hilo, HI, 96720, USA
⁴ LERMA, Observatoire de Paris, College de France, PSL, CNRS, Sorbonne Univ., UPMC, 75014 Paris, France
⁵ Observatorio Astronómico Nacional (OAN) – Observatorio de Madrid, Alfonso XII 3, 28014 Madrid, Spain

Received: 30 July 2016
Accepted: 22 November 2016

Abstract

NGC 1808 is a nearby barred spiral galaxy which hosts young stellar clusters in a patchy circumnuclear ring with a radius of ~240 pc. In order to study the gaseous and stellar kinematics and the star formation properties of the clusters, we perform seeing-limited H + K-band near-infrared integral-field spectroscopy with SINFONI of the inner ~600 pc. From the M_BH−σ_∗ relation, we find a black hole mass of a few 10⁷M_⊙. We estimate the age of the young stellar clusters in the circumnuclear ring to be ≲10 Myr. No age gradient along the ring is visible. However, the starburst age is comparable to the travel time along the ring, indicating that the clusters almost completed a full orbit along the ring during their lifetime. In the central ~600 pc, we find a hot molecular gas mass of ~730 M_⊙ which, with standard conversion factors, corresponds to a large cold molecular gas reservoir of several 10⁸M_⊙, in agreement with CO measurements from the literature. The gaseous and stellar kinematics show several deviations from pure disc motion, including a circumnuclear disc and signs of a nuclear bar potential. In addition, we confirm streaming motions on the ~200 pc scale that have recently been detected in CO(1-0) emission. Thanks to the enhanced angular resolution of <1″, we find further streaming motion within the inner arcsecond that had not been detected until now. Despite the flow of gas towards the centre, no signs of significant AGN activity are found. This raises the question: will the infalling gas fuel an AGN or star formation?