Coordinated Assembly of Galaxy Groups and Clusters in the IllustrisTNG
  Simulations
  Recent stellar population analysis of early-type galaxy spectra has
demonstrated that the low-mass galaxies in cluster centers have high
[$\alpha/\rm Fe$] and old ages characteristic of massive galaxies and unlike
the low-mass galaxy population in the outskirts of clusters and fields. This
phenomenon has been termed "coordinated assembly" to highlight the fact that
the building blocks of massive cluster central galaxies are drawn from a
special subset of the overall low-mass galaxy population. Here we explore this
idea in the IllustrisTNG simulations, particularly the TNG300 run, in order to
understand how environment, especially cluster centers, shape the star
formation histories of quiescent satellite galaxies in groups and clusters
($M_{200c,z=0}\geq10^{13} M_{\odot}$). Tracing histories of quenched satellite
galaxies with $M_{\star,z=0}\geq10^{10} M_{\odot}$, we find that those in more
massive dark matter halos, and located closer to the primary galaxies, are
quenched earlier, have shorter star formation timescales, and older stellar
ages. The star formation timescale-$M_{\star}$ and stellar age-$M_{\star}$
scaling relations are in good agreement with observations, and are predicted to
vary with halo mass and cluster-centric distance. The dependence on environment
arises due to the infall histories of satellite galaxies: galaxies that are
located closer to cluster centers in more massive dark matter halos at $z=0$
were accreted earlier on average. The delay between infall and quenching time
is shorter for galaxies in more massive halos, and depends on the halo mass at
its first accretion, showing that group pre-processing is a crucial aspect in
satellite quenching.
