NGC 5084: A Massive Disk Galaxy Accreting its Satellites?

The spectra of 34 galaxies within 20 arcmins ( ~ 100 kpc) of the lenticular galaxy NGC 5084 have been obtained using the FOCAP system on the Anglo-Australian 3.9m telescope. Nine objects are found with projected separations ≲ 80 kpc and with radial velocities within +/- 630 km s(-1) of the parent galaxy redshift. Using various techniques, their velocity differences and projected separations are used to estimate the mass of this S0 galaxy, which ranges from 6 x 10(12) Msun to 1 x 10(13) Msun. With such a mass, NGC 5084 is one of the most massive disk galaxy known, with a (M/L_B) gtrsim 200 Msun/Lsun. In agreement with the models' predictions of Quinn & Goodman (1986) but contrary to the results of Zaritsky et al (1993) obtained from their statistical sample, the properties of the satellites' population show no evidence for the ``Holmberg effect'' and a clear excess of satellites in retrograde orbits. Several signs hint that this S0 galaxy has survived the accretion of several satellites.