Context :

Aims : We investigate the stellar kinematics and line strength indices in the outer halos of brightest cluster galaxies ( BCGs ) in the Coma cluster to obtain the outer halo V _ { rot } and \sigma profiles and to derive constraints on the formation history of these objects .

Methods : We analyzed absorption lines in deep , medium-resolution , long-slit spectra in the wavelength range \sim 4500 - 5900 Å , out to \sim 50 kpc for NGC 4874 and \sim 65 kpc for NGC 4889 , probing regions with a surface brightness down to \mu _ { R } \sim 24 mag arcsec ^ { -2 } .

Results : These data provide stellar velocity and velocity dispersion profiles along the major axes of both BCGs , and also along the minor axis of NGC 4889 .
The kinematic properties of NGC 4874 and NGC 4889 halos extend the previous relations of early-type galaxy halos to bright luminosities and indicate that the stars in the outer regions are still bound to these galaxies .
For NGC 4889 we also determine H \beta Mg and Fe line strength indices , finding strong radial gradients for Mg and Fe .
The current dataset for NGC 4889 is one of the most extended in radius , including both stellar kinematics and line strength index measurements .

Conclusions :