The Circumnuclear Star Formation Environment of NGC 6946: Br-gamma and H2 Results from Keck Integral Field Spectroscopy

TL;DR

This study uses high-resolution integral field spectroscopy to analyze star formation and gas dynamics in the nuclear region of NGC 6946, revealing the distribution of HII regions, molecular gas, and star clusters within the central 520 parsecs.

Contribution

First detailed 3D near-infrared spectroscopic analysis of NGC 6946's nuclear star formation environment at 10 parsec scales.

Findings

Giant HII regions are concentrated within 70pc of the galaxy center.

H2 emission is confined within 60pc, similar to HCN distribution.

Gas-assisted migration may contribute to nuclear star cluster buildup.

Abstract

We present a 3-dimensional data cube of the K band continuum and the Br-gamma, H2 S(0) and S(1) lines within the central 18.5" x 13.8" (520 pc x 390 pc) region of NGC 6946. Data were obtained using OSIRIS, a near-infrared Integral Field Unit at Keck Observatory, with Laser Guide Star Adaptive Optics. The 0.3" resolution allows us to investigate the stellar bulge and the forming star clusters in the nuclear region on 10 parsec scales. We detect giant HII regions associated with massive young star clusters in the nuclear spiral/ring (R ~ 30pc) and in the principal shocks along the nuclear bar. Comparisons of the Br-gamma fluxes with Pa-alpha line emission and radio continuum indicate A_K ~ 3, A_V ~ 25 for the nuclear star forming regions. The most luminous HII regions are restricted to within 70pc of the center, despite the presence of high gas columns at larger radii (R ~ 200pc). H2 emission is restricted to clouds within R ~ 60pc of the center, and in this sense resembles the distribution of the HCN line emission. We propose that gas-assisted migration of the young star clusters is contributing to the buildup of the nuclear bar and nuclear star cluster (R < 30pc) in this galaxy.