The structure and content of NGC 6822.
Abstract
Photoelectric and photographic studies of surface brightness and color, and of individual stars and nonstellar objects, in NOC 6822 are used to establish the galaxy's structure and content. Its bar has a position angle of 100 + 30 and a mean ellipticity of 0.47 + 0.18. Its peak surface brightness is V = 21.4 mag arcsec -2, and isophotes are given out to V = 24.0. Star counts on five plates are used to compare the star density distribution with the surface brightness; the stellar luminosity function is found to vary across the galaxy, in relation to the bar. Luminosity proffles and stellar density profiles show an overall exponential decrease outward, with a slope of 0.37 1 0.05 mag arcmin . The minor axis of the bar, on the other hand, has a slope that depends on the objects sampled, being much steeper for the supergiant (resolved) stars than for the luminosity in general. The mean color of the galaxy is B - V = 0.79 1 0.06, U - = 0.04 + 020 and the reddening is E(B - V) = 0.28 + 0.03. Sixteen OB associations are cataloged and compared with those in other galaxies. Their spatial distribution is similar to that of the LMC, as are the size distribution and the relationship between size and stellar density. Their mean diameter is 163 pc. A study of 30 star clusters shows that NGC 6822 is normal in its population of these objects. Photoelectric integrated data for the brightest show normal UBV colors. The cluster luminosity function and age function are similar to those of the Magellanic Clouds, after allowance is made for the different galaxy luminosities. The H ii regions are rediscussed, and their size distribution is compared with those for other galaxies. Agreement with Sandage and Tammann's (1974) halo diameters for the three largest is good. Eleven discrete dust clouds are identified and compared with those of other galaxies. They average 39 pc in diameter, about the same as those of the SMC, but are of somewhat smaller opacity. Subject headings: galaxies: individual - galaxies: photometry - galaxies: stellar content - galaxies: structure
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- January 1977
- DOI:
- 10.1086/190419
- Bibcode:
- 1977ApJS...33...69H