Kinematics and line strength indices in the halos of the Coma brightest cluster galaxies NGC 4874 and NGC 4889

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 similar to 4500-5900 angstrom, out to similar to 50 kpc for NGC 4874 and similar to 65 kpc for NGC 4889, probing regions with a surface brightness down to mu(R) similar to 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.