A SEARCH FOR DARK-MATTER IN ELLIPTIC GALAXIES - RADIALLY EXTENDED SPECTROSCOPIC OBSERVATIONS FOR 6 OBJECTS

Within the ESO Key Programme ''A search for dark matter in elliptical galaxies'', we have performed a detailed study of the large scale stel lar kinematics of NGC 1400, 4946, 5812, 6721, 7507, and 7796. Our obse rvations have produced kinematical data down to the 24.1 mag arcsec(-2 ) in the B band, i.e. in some cases out to 2 R(e) and beyond. NGC 1400 , 4946, and 6721 show significant rotation. The other three galaxies ( NGC 5812, 7507, and 7796) can be described by spherical non-rotating e quilibrium models. For two of these objects self-consistent stellar dy namical models with constant mass-to-light ratio are found to give goo d fits to the photometric and kinematical data, although the presence of dark matter is not excluded. In contrast, NGC 7796 shows evidence f or the presence of a dark halo. This galaxy also exhibits counterrotat ion inside 4'' and, correspondingly, a central peak in the velocity di spersion profile. On the basis of the small sample of objects studied so far, with radially extended spectroscopic observations, possible tr ends in the size of dark halos around elliptical galaxies are pointed out.