The Three Hundred Project: deducing the stellar splashback structure of galaxy clusters from their orbiting profiles

We examine the splashback structure of galaxy clusters using hydrodynamical simulations from the GIZMO run of The Three Hundred Project, focusing on the relationship between the stellar and dark matter components. We dynamically decompose clusters into orbiting and infalling material and fit their density profiles. We find that the truncation radius rt, associated with the splashback feature, coincides for stars and dark matter, but the stellar profile exhibits a systematically steeper decline. Both components follow a consistent rt − Γ relation, where Γ is the mass accretion rate, which suggests that stellar profiles can be used to infer recent cluster mass growth. We also find that the normalisation of the density profile of infalling material correlates with Γ, and that stellar and dark matter scale radii coincide when measured non-parametrically. By fitting stellar profiles in projection, we show that rt can, in principle, be recovered observationally, with a typical scatter of ~0.3 R200m. Our results demonstrate that the splashback feature in the stellar component provides a viable proxy for the cluster’s physical boundary and recent growth by mass accretion, offering a complementary observable tracer to satellite galaxies and weak lensing.