In order to study the internal dynamics of actual galaxy pairs , we need to derive the probability distribution function ( PDF ) of true 3D ( orbital ) intervelocities and interdistances between pair members from their observed ( projected ) values , and of the pair masses from Kepler ’ s third law .
Our Isolated Galaxy Pair Catalog ( IGPC ) of 13114 pairs [ 15 ] is used here for this research .
The algorithms of statistical deprojection elaborated in [ 16 ] are applied to these observational data .
We derive the orbital velocity PDFs for the whole catalog and for several selected subsamples .
The interdistance PDF is deprojected and compared to analytical profiles which are expected from semi-theoretical arguments .
The PDF of deprojected pair orbital velocities is characterized by the existence of a main probability peak around \approx 150 km.s ^ { -1 } for all subsamples of the IGPC as well as for the UGC pair catalog [ 2 ] .
The interdistance PDFs of both the projected and deprojected data are described at large distances by the same power law with exponent \approx - 2 .
The whole distributions , including their cores , are fairly fitted by King profiles .
The mass deprojection yields a mass/luminosity ratio for the pairs of M / L = ( 30 \pm 5 ) in Solar units .
The orbital velocity probability peak is observed at the same value , \approx 150 km/s , as the main exoplanet velocity peak , which points toward a possible universality of Keplerian structures , whatever the scale .
The pair M / L ratio is just 5 times the standard ratio for luminous matter , which does not require the existence of non-baryonic dark matter in these systems .