Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...467..227e&link_type=abstract
Astrophysical Journal v.467, p.227
Astronomy and Astrophysics
Astronomy
27
Galaxies: Individual Ngc Number: Ngc 6946, Galaxies: Photometry, Galaxies: Starburst, Infrared: Galaxies
Scientific paper
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 10^52^ ionizing photons s^-1^. A thorough examination of the gas and stellar motions puts a 2 σ 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 x 10^8^ M_sun_. A detailed study of broadband colors, emission-line ratios, and the 10 micron silicate absorption feature indicates that the extinction to the starburst is high, with A_V_ = 10.4 mag. An estimate of the supernova rate from both nonthermal radio emission and [Fe II] 1.644 micron emission from gas excited in fast shocks agrees well with our models. The current rate of supernova explosions in the nucleus is ~6 x 10^-3^ yr^- 1^. The bolometric luminosity of the starburst region is greater than 2.2 x 10^9^ L_sun_. 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 H_2_ emission lines. We have measured the lines of H_2_ 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.
Engelbracht Chad W.
Latter William B.
Rieke George H.
Rieke Marcia J.
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