The Structure and Content of NGC 205

Abstract

view Abstract Citations (151) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Structure and Content of NGC 205 Hodge, Paul W. Abstract The structure and the content of NGC 205, an elliptical galaxy companion to M3 1, is studied by means of a series of photoelectric and photographic measurements. Isophotometry of the galaxy provides information on its detailed shape, and was carried out in three colors on the UB V system. The isophotes are elliptical in the center and intermediate regions, but show distortion in the outer regions, probably due to tidal interaction with M3 1. The ellipticity is found to be variable from the center outward ranging from E = 0.35 in the center to E = 0.50 in the outer parts. The direction of the major axis, 0, is variable, primarily because of the distortion of the isophotes in the outer regions. Luminosity profiles based on direct photoelectric measurements from the center along the north-south and east-west axes are presented. From these, and using isophotes, the major- and minor-axis profiles are obtained and are compared with measures made previously by others. The comparison shows reasonably good agreement with previous direct photoelectric measurements but rather poor agreement in the outer regions with previous photographic photometry. A comparison of the profiles with theoretical models of elliptical galaxies shows excellent agreement. The galaxy is found to have an anomalous color distribution for an elliptical galaxy, with the center being decidedly bluer than the outer regions. This is interpreted to be the result of the presence in the central area of a number of bright 0- and B-type stars, as first detected photographically by Baade. Examination of Hale Observatory plates in the blue and ultraviolet provides information on the number and distribution of the resolved 0- and B-type stars in the central area of NOC 205. They are found to lie in an elliptical area almost but not quite centered on the center of NOC 205 and having a mean dimension of approximately 340 p.c. The centroid of the OB stars is approximately 45 p.c. from the nucleus of the system. The brightest star is estimated to have an apparent magnitude of B = 19.42 and the faintest discernible on the plates examined, a magnitude of B = 21.01, corresponding to absolute magnitudes of Mv = -5.3 and -3.7, respectively. It is estimated that the age of the complex is on the order of 5 x 106 years. The luminosity function suggests that the total mass of Population I stars involved is between 2 >c 106 and 2 x 10a , depending on the assumptions regarding the unseen portion of the luminosity function. Twelve dark nebulae are identified, and their distribution is found to be similar to the distribution of OB stars, with the exception that the largest and most conspicuous dust clouds lie outside of the area inhabited by these stars. The average dimension of the dust clouds corresponds to a linear dimension of approximately 33 pc. Photometric properties of three of the dust clouds are obtained by photographic and photoelectric measurements. From pure photoelectric measurements in the UB V systems, the ratio of general to selective absorption in one of the dust clouds is found to be approximately A VIA(B - V) = 3.4 i 0.6, in good agreement with the solar-neighborhood value. Masses estimated for the dust regions range from 10 to 460 a Lick Observatory 120-inch telescope photoelectric measurements of the brightness and colors of all of the eight globular star clusters known for this system provide a luminosity function for these objects that is compared with the luminosity function for the clusters in M31 and found to lie approximately 2 mag fainter than the latter. The colors are found to be normal within the accuracy of the measurements. Subject headings: galactic structures - galaxies, individual - galaxies, photometry of Publication: The Astrophysical Journal Pub Date: June 1973 DOI: 10.1086/152176 Bibcode: 1973ApJ...182..671H full text sources ADS | data products SIMBAD (14) NED (1)