Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987apjs...64..427s&link_type=abstract
Astrophysical Journal Supplement v.64, p.427
Astronomy and Astrophysics
Astronomy
61
Galaxies: Clustering, Luminosity Function
Scientific paper
New high-accuracy (< σv > ≡ 9 km s-1) radial velocities and photoelectric magnitudes V for a complete sample of 96 galaxies in 48 southern pairs, published in Papers I and II, are here analyzed with a Monte Carlo method to estimate mass-to-light ratios of galaxies at spatial separations of the order of 10O kpc. Special emphasis has been placed on adopting stringent sample selection procedures based on an objective dynamical model. As part of the analysis, we have applied a probabilistic correction for inclusion of optical pairs, and devised an empirical Monte Carlo procedure to allow for biases due to accidental exclusion of bound pairs. Dynamical simulations were again employed to test a variety of dynamical models, through the variables. From our observations and analysis, the following conclusions are drawn: (1) The ratio of orbital mass to visual luininosity for type Sc galaxies ranges from 12 to 32, with a most likely value of M/Lv = 21±5 solar units; the value for elliptical galaxies ranges from 22 to 60 with a most likely value of M/Lv = 39±9 (H0 = 50). Despite these relatively low values, masses deterinined from our sample are few times larger than masses obtained from rotation curves, adding supporting evidence for a "mass discrepancy." (2) Models with moderately high eccentricity orbits seem to represent the data better than models with nearly circular orbits. (3) Correlations between dynamical variables suggest that Keplerian orbits are a good representation of the true orbits. This, plus the fact that mass appears to be independent of projected separation beyond 60-100 kpc, suggests that mass distributions of binary galaxies extend less far than their mean separation. (4) The distribution of projected pair separations is fitted by a lognormal distribution. Arguments based on the effect of mergers suggest that power-law distributions used in previous analyses are inappropriate and "scale-free" models of binary galaxies should be viewed with caution. A crucial power-law fit made by Turner is shown to be erroneous. (5) The luminosity distribution of galaxies in our sample agrees with that of Schechter, suggesting that there is no excess of bright binary galaxies, and that M/L ratios derived from binaries hold as well for isolated field galaxies.
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