Dynamic and spatial properties of satellites in isolated galactic systems

Abstract

Using the NYU Value-Added Galaxy Catalog (NYU-VAGC) I examine the line-of-site velocity dispersion of satellite galaxies orbiting larger, isolated, primary galaxies. The line-of-sight dispersion can be directly compared to the functional form of three models (NFW, MOND and a relic neutrino based model) that diverge at large distances allowing discrimination between models. The algorithm used to determine the primary and satellite samples yielded 2741 primary galaxies and 4966 possible satellites. After removing foreground/background interloper galaxies, I found the NFW model is the most probable. This agrees well with other published results which find that the density of the dark matter halo declines as p µ r-3. The neutrino model has large probabilities and cannot be completely excluded as a possible explanation of the observed velocity dispersions. The MOND model had small probabilities of fitting the velocity dispersion, and results of higher dispersions found for early type primaries than those found for late type primaries of the same luminosity make MOND unlikely.

From the data I find no evidence of the Holmberg Effect. Satellite galaxies tend to be isotropic both at small projected distances from the primary galaxy and at large projected distances (at the 1 sigma level) from the primary galaxy. However, I do find that the distribution of early type satellites tends to decline more steeply than the late type satellites in a high magnitude primary sample.