Description
Galaxy evolution is profoundly shaped by environmental processes, yet disentangling internal quenching mechanisms from large-scale influences remains a key challenge. The two-halo galactic conformity effect—the spatial correlation in galaxy properties extending beyond halo virial radius to ~4 Mpcs—further complicates the disentanglement of internal and external quenching processes. Using SDSS data and IllustrisTNG simulations, we explore how central galaxies’ star formation relates to their large-scale environments via a novel metric $\Sigma_{\text{cen, 5th}}$, tracing density using neighboring centrals. We uncover two environmental signatures: low-mass centrals in dense regions show suppressed star formation, linked to "backsplash" galaxies previously associated with massive halos, while massive centrals in sparse regions exhibit enhanced star formation, reflecting reduced merger activity and delayed bulge/black hole growth. Simulations replicate the low-mass trend through backsplash dynamics but fail to capture the massive galaxy signal, highlighting gaps in modeling AGN feedback and merger histories. These results emphasize the dual role of environment—past interactions imprint conformity in low-mass systems, while large-scale underdensities preserve disk-dominated massive galaxies—underscoring the need to integrate environmental history and super-halo-scale processes into galaxy evolution models.
