Observations and modeling of the nuclear starburst in NGC 69461

C. W. Engelbracht, Marcia J Rieke, George H. Rieke, William B. Latter

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)227-240
Number of pages14
JournalAstrophysical Journal
Volume467
Issue number1 PART I
StatePublished - 1996
Externally publishedYes

Fingerprint

modeling
supernovae
stellar motions
broadband
nuclei
estimates
radio emission
gases
slits
explosions
narrowband
star formation
silicates
extinction
infrared spectra
gas
examination
apertures
shock
luminosity

Keywords

  • Galaxies: individual (NGC 6946)
  • Galaxies: photometry
  • Galaxies: starburst infrared: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Observations and modeling of the nuclear starburst in NGC 69461. / Engelbracht, C. W.; Rieke, Marcia J; Rieke, George H.; Latter, William B.

In: Astrophysical Journal, Vol. 467, No. 1 PART I, 1996, p. 227-240.

Research output: Contribution to journalArticle

Engelbracht, CW, Rieke, MJ, Rieke, GH & Latter, WB 1996, 'Observations and modeling of the nuclear starburst in NGC 69461', Astrophysical Journal, vol. 467, no. 1 PART I, pp. 227-240.
Engelbracht, C. W. ; Rieke, Marcia J ; Rieke, George H. ; Latter, William B. / Observations and modeling of the nuclear starburst in NGC 69461. In: Astrophysical Journal. 1996 ; Vol. 467, No. 1 PART I. pp. 227-240.
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AB - 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.

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