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

TL;DR

This study uses high-resolution near-infrared spectroscopy to analyze gas and stellar dynamics, star formation, and potential AGN activity in the central 600 parsecs of galaxy NGC 1808, revealing complex motions and recent starburst activity.

Contribution

It provides new high-resolution integral-field spectroscopic data revealing detailed gas and stellar kinematics, star formation history, and gas inflow patterns in NGC 1808's nucleus.

Findings

Young stellar clusters are less than 10 Myr old with no age gradient.

Detected streaming motions and deviations from pure disc rotation.

Large cold molecular gas reservoir present without active AGN signs.

Abstract

NGC 1808 is a nearby barred spiral galaxy which hosts young stellar clusters in a patchy circumnuclear ring with a radius of $\sim 240\,\mathrm{pc}$. 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 $\sim 600\,\mathrm{pc}$. From the $M_\mathrm{BH}-\sigma_*$ relation, we find a black hole mass of a few $10^7\,M_\odot$. We estimate the age of the young stellar clusters in the circumnuclear ring to be $\lesssim 10\,\mathrm{Myr}$. 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 life time. In the central $\sim 600\,\mathrm{pc}$, we find a hot molecular gas mass of $\sim 730\,M_\odot$ which, with standard conversion factors, corresponds to a large cold molecular gas reservoir of several $10^8\,M_\odot$, in accordance 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 $\sim 200\,\mathrm{pc}$ scale that have recently been detected in CO(1-0) emission. Due to our enhanced angular resolution of $<1\,\mathrm{arcsec}$, we find further streaming motion within the inner arcsecond, that have not been detected until now. Despite the flow of gas towards the centre, no signs for significant AGN activity are found. This raises the questions what determines whether the infalling gas will fuel an AGN or star formation.