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M49 (NGC 4472) is the dominant galaxy in subcluster B of the Virgo Cluster,and a benchmark for studying the build-up of the extended halos of brightestgroup galaxies in the outskirts of galaxy clusters. We investigate thekinematics in the outer halo of M49, look for substructures, and describe thetransition to the surrounding intra-group light. As kinematic tracers we useplanetary nebulae (PNe), combining kinematics from the extended PlanetaryNebula Spectrograph (PN.S) early-type galaxy survey with our recent deepphotometric sample. We study the position-velocity-plane for bright and faintPN populations out to 95 kpc radius, and employ a multi-Gaussian model for thevelocity distribution to identify stellar populations with distinct kinematicsand histories. We report the detection of stellar-kinematic substructureassociated with the interaction of M49 with the dwarf irregular galaxy VCC1249. We find two kinematically distinct PN populations associated with themain M49 halo and the extended intra-group light (IGL). These have velocitydispersions $\sigma_{halo}\simeq 170$ km/s and $\sigma_{IGL} \simeq400$ km/s at10-80 kpc radii. The overall luminosity profile and velocity dispersion at$\sim80$ kpc are consistent with a flat circular velocity curve extrapolatedfrom X-ray observations. The dispersion of the PNe associated with the IGLjoins onto that of the satellite galaxies in subcluster B at $\sim100$ kpcradius. This is the first time that the transition from halo to IGL is observedbased on the velocities of individual stars. Therefore the halo of M49,consisting of at least three distinct components, has undergone an extendedaccretion history within its parent group potential. The blue colours of theIGL component are consistent with a population of stars formed in low-massgalaxies at redshift $\sim0.5$ that has since evolved passively, as suggestedby other data.

Three dynamically distinct stellar populations in the halo of M49