Abstract

We analyze spatially resolved and co-added SDSS-IV MaNGA spectra with signal-to-noise ratio similar to 100 from 2200 passive central galaxies (z similar to 0.05) to understand how central galaxy assembly depends on stellar mass (M (*)) and halo mass (M ( h )). We control for systematic errors in M ( h ) by employing a new group catalog from Tinker and the widely used Yang et al. catalog. At fixed M (*), the strengths of several stellar absorption features vary systematically with M ( h ). Completely model-free, this is one of the first indications that the stellar populations of centrals with identical M (*) are affected by the properties of their host halos. To interpret these variations, we applied full spectral fitting with the code alf. At fixed M (*), centrals in more massive halos are older, show lower [Fe/H], and have higher [Mg/Fe] with 3.5 sigma confidence. We conclude that halos not only dictate how much M (*) galaxies assemble but also modulate their chemical enrichment histories. Turning to our analysis at fixed M ( h ), high-M (*) centrals are older, show lower [Fe/H], and have higher [Mg/Fe] for M ( h ) > 10(12) h (-1) M (circle dot) with confidence >4 sigma. While massive passive galaxies are thought to form early and rapidly, our results are among the first to distinguish these trends at fixed M ( h ). They suggest that high-M (*) centrals experienced unique early formation histories, either through enhanced collapse and gas fueling or because their halos were early forming and highly concentrated, a possible signal of galaxy assembly bias.