Near-infrared images in both broad and narrow bands, plus long-slit and aperture spectroscopy at moderate and high resolution have been obtained for NGC 6946. We have used these data and data from the literature to derive a set of observational constraints on the stellar population in the nucleus. We estimate an ultraviolet flux of 1052 ionizing photons s-1. A thorough examination of the gas and stellar motions puts a 2 a upper limit on the dynamical mass in the central 8″5 (which corresponds to 230 pc at an assumed distance of 5.5 Mpc) of ∼3 × 108 M⊙. A detailed study of broadband colors, emission-line ratios, and the 10 μm silicate absorption feature indicates that the extinction to the starburst is high, with Av = 10.4 mag. An estimate of the supernova rate from both nonthermal radio emission and [Fe II] 1.644 μm emission from gas excited in fast shocks agrees well with our models. The current rate of supernova explosions in the nucleus is ∼6 × 10-3 yr-1. The bolometric luminosity of the starburst region is greater than 2.2 × 109 L⊙. In addition to the diagnostic features we have used here, the infrared spectra show a wealth of stellar features and weaker emission lines, including atomic absorption lines and several H2 emission lines. We have measured the lines of H2 and compared the ratios to models to determine the excitation mechanism. The properties of NGC 6946 have been fitted with a starburst model. We find that the starburst probably had a duration of ∼20 million years and that the star formation is likely to be biased toward high-mass stars compared with those in the local neighborhood.
- Galaxies: individual (NGC 6946)
- Galaxies: photometry
- Galaxies: starburst infrared: galaxies
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science