Dwarf satellite galaxies — the faint, low-mass companions orbiting larger hosts — are sensitive probes of cosmology. Their abundance, spatial distribution, and survival rates depend on the dark matter model, the physics of galaxy formation, and the environment they inhabit. Most studies control for host mass and redshift. Few control for cosmic environment — whether the host sits in a void, a filament, a group, or a cluster.
Cuesta-Lazaro, Santos-Santos, and Domínguez-Tenreiro (arXiv 2602.22485, February 2026) show that environment is the primary driver. Using the Millennium simulation with semi-analytic galaxy formation models, they compare dwarf satellite populations across cosmic environments from redshift 2 to the present.
Dense environments suppress satellite populations relative to voids. But the effect is not simply “more neighbors, fewer satellites.” The spatial distribution changes qualitatively: voids produce strongly centrally concentrated satellite populations, clusters produce flattened radial distributions, and groups show intermediate patterns. The evolutionary pathways diverge: voids accumulate satellites gradually over cosmic time, groups show mass-dependent patterns, and clusters exhibit strong late-time suppression as tidal stripping and ram-pressure removal destroy dwarfs that would have survived in quieter settings.
Host stellar mass matters, but less than environment. Cosmic epoch matters, but less than environment. The hierarchy of importance is inverted from the standard assumption, which treats host mass as the primary predictor and environment as a secondary correction.
The satellite population is not just a function of its host. It is a function of what surrounds the host — the large-scale density field within which the entire system is embedded. LSST, Euclid, and the Roman Space Telescope will test whether the real universe follows this prediction. The satellites carry the signature of the cosmic web.