The Nuclear Gas Dynamics and Star Formation of NGC 7469

Abstract

We report interferometric radio CO2-1 observations at a resolution of 0.7", and 0.085" resolution adaptive optics K-band spectroscopy of the inner few arcseconds of NGC7469. The CO2-1 map shows a ring of molecular clouds and a bright extended nucleus, with a bar or pair of spiral arms between them. The dynamical structure of both the radio CO2-1 and the K-band H2 1-0S(1) lines can be reproduced using an axisymmetric mass model comprising 3 components: a broad disk, a ring 4-5" across, and an inner nuclear ring about 0.5" across. No non-circular motions faster than the velocity residuals of 25 km/s are seen, although this may be because in some cases a secondary bar is not expected to cause gas inflow. From the dynamical mass and estimates of the stellar mass we find that the CO-to-H_2 conversion is 0.4-0.8 times that for the Milky Way. The H2 1-0S(1) morphology peaks at the nucleus, although there is no strong nuclear mass concentration. The 1-0S(1) is likely to originate in X-ray of gas by the AGN rather than via star formation. Using the 2.3um stellar CO2-0 absorption and the continuum slope we have directly resolved the nuclear star cluster to be 0.15-0.20" across, and find that it is asymmetric. This cluster has an age of less than about 60Myr and contributes 20-30% of the nuclear K-band light, and about 10% of the nuclear bolometric luminosity. Within a radius of ~4" gas contributes more than half the total mass; but in the nucleus, within a radius of 0.1", it is likely that most of the mass is due to stars