Physics
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aps..ses..db02g&link_type=abstract
American Physical Society, Southeastern Section Meeting, November 13-15, 1998 Miami, Florida, abstract #DB.02
Physics
Scientific paper
We discuss HI observations and analyses of the kinematics of 25 satellite-primary galaxy pairs with projected separations between 4.9 and 240 kpc. The satellites have masses less than 3% of their primary spirals. Two estimates for their mass are available, one from their rotation curves and one from the orbital properties of the satellites. Defining \chi as the ratio of these two estimates, it is a measure of the presence or absence of a significant halo. The \chi distribution of these 24 pairs is presented and selection effects are considered. In addition, we show that the \chi distribution of more numerous pairs, with projected separations of less thn 200 kpc, identified by Zartisky and colleagues (employing selection criteria quite different than ours) is similar to ours. We show that the observational biases have a negligible effect; the biased and unbiased distributions are essentially identical. In order to understand this distribution, N-body calculations were executed to simulate the dynamical behavior of relatively low mass satellites orbiting primary disk galaxies with and without extended halos. The models and the real galaxies were 'obseved' in the same fasion. In adition, we made a partially analytical analysis of the behavior of orbits in a logarithmic potential. We find that a 'generic' model, characterizd by a single disk/halo combination, cannot reproduce the observed distribution, P(\chi). However, a simple two component population of galaxies, composed of not more than 60% with halos and 40% without halos, is successful, if galaxies have dimensions of order 200kpc. If galaxies are considerably larger with sizes extending 400 kpc or more, the constraints become more onerous. No generic model can describe the full range of the observed P(\chi), particularly if the distribution for r_p<200 kpc is compared with that for r_p>200 kpc. Regardless of the mix of orbital eccentricities, nether pure halo, nor cannonical models (disk and halo masses are comparable within the disk radius) will work. A muticomponent approximation to reality can be constructed for which the cannonical model must be mixed with a small fraction of systems essentialy devoid of a massive dark halo. Only by including thes complexities can the full range of P(\chi) be modeled with any degree of success over all radial extents. Furthermore, dynamical friction cannot be ignored. The average mass of a galaxy is in the range of (1-5)x10^12Mo. This is insufficient to close the universe.
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