Origins of the 12-200 micron flux in NGC 6946 - Starlight and continuum dust emission from an SC galaxy

Abstract

view Abstract Citations (51) References (104) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Origins of the 12--200 Micron Flux in NGC 6946: Starlight and Continuum Dust Emission from an SC Galaxy Engargiola, G. Abstract We mapped NGC 6946 in continuum dust emission at 100, 160, and 200 microns with a ^3^He cooled array of 32 bolometer detectors, and in the g band, r band, and Hα+[N II] with a large-format CCD camera. The beam-widths of the far-infrared camera were 45" at 100 and 160 microns and 56" at 200 microns; the optical images were smoothed to the resolution of the far-infrared images. Also, we present maps of the galaxy at 12, 25, and 60 microns, made with 1' resolution from Infrared Astronomical Satellite (IRAS) data processed with a Lucy-Richardson deconvolution algorithm. Continuum dust emission is studied in relation to spiral and radial structure, to the distribution of the interstellar medium, and to ionizing and nonionizing radiation from stars. This paper attempts to clarify the sources of dust heating, the optical and spectral characteristics of the nuclear source and disk, the properties of dust grains, and the origins of infrared luminosity in NGC 6946. The 60, 100, 160, and 200 micron continuum distributions show discrete sources coinciding with giant H II regions superposed on a smooth, unresolved disk background which decreases exponentially with radius. Sources which coincide with giant H II region complexes are more prominent relative to the disk at shorter wavelengths; a few sources brightest at 160 and 200 microns indicate dust grains cooler than 18 K. Emission parameters {TAU}, β, and τ(100), derived from the far- infrared continuum data, vary with position in the disk. Sixty-four percent (7.5 X 10^9^ L_sun_) of the stellar luminosity in the central 45", and 35% (3.4 X 10^10^ L_sun_) in the central 5', is absorbed by dust; also, we estimate that 25% (5.3 x 10^10^ L_sun_) of the total stellar luminosity in the disk is absorbed by dust. Approximately 5% of the total 160 micron luminosity originates beyond the 25 mag arcsec^-2^ blue isophote, where dust temperatures are less than 18 K. Infrared luminosities of cool dust (~15-24 K) in quiescent interstellar gas, and warm dust (>29 K) in complexes of massive star formation, are estimated with a two-component model. The distribution of infrared emission from cool dust (25%-30% of the total infrared luminosity of the galaxy) agrees with the results of an analytic model describing transport of stellar photons in the neutral interstellar medium. Stars having m < 10 M_sun_ embedded in optical depths for visual absorption of 0.5 or less cover an estimated 90% of the total surface area of the galactic disk; these stars generate 70% of the total stellar luminosity, or approximately 60% of the total bolometric luminosity. Publication: The Astrophysical Journal Supplement Series Pub Date: July 1991 DOI: 10.1086/191583 Bibcode: 1991ApJS...76..875E Keywords: Cosmic Dust; Galactic Radiation; Infrared Astronomy; Infrared Radiation; Spiral Galaxies; Stellar Radiation; Brightness Distribution; Continuous Radiation; H Ii Regions; Infrared Astronomy Satellite; Infrared Photometry; Infrared Spectra; Luminous Intensity; Visible Spectrum; Visual Photometry; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 6946; GALAXIES: INTERSTELLAR MATTER; INFRARED: SPECTRA full text sources ADS | data products SIMBAD (6) NED (1)