What are the progenitors of the intragroup light stars around M49?

The interactions between galaxies in dynamically rich environments like clusters and groups of galaxies lead to the libration of stars that form the diffuse intra-cluster or intra-group light (IGL). The IGL is a good laboratory to study the properties of late-accreted satellites in the proximity of the brightest group galaxy and to compare these to cosmological simulations.
To overcome the challenges posed by the extremely low surface brightness of the diffuse IGL, we use planetary nebulae (PNe) as tracers of the IGL. Their individual line-of-sight velocities can be easily measured even at distances of the Coma Cluster (100 Mpc). In M49 (NGC 4472), the brightest galaxy in the Virgo Cluster and centre of the Subcluster B, we are able to measure a rising galaxy velocity dispersion from the velocities of individual stars (PNe) reaching that of the Subcluster B at large radii. This is a tell-tale sign of halo-to-IGL transition.
Based on the IGL kinematics, its smooth morphology and strong blueward colour gradient, we infer that the progenitors of the IGL stars had to be old (> 5 Gyr) and metal-poor ([Fe/H] << -1). Hence they would lie on the low-mass end of the mass-metallicity relation (<10^8 M_sun), being 1000 times less massive than M49. This low mass challenges the predictions from hydrodynamical cosmological simulations, which indicate more massive and metal-rich galaxies as progenitors of the IGL. Our results provide new insights on the assembly of the Virgo Subcluster B IGL and place constraints on the feedback mechanisms in cosmological simulations as they currently underestimate the star formation in low-mass satellite galaxies.