Accretion of Galaxy Groups into Galaxy Clusters

Abstract

We study the role of group infall in the assembly and dynamics of galaxy clusters in $\Lambda$CDM. We select $10$ clusters with virial mass $M_{200}\sim 10^{14}{M}_{\odot }$ from the cosmological hydrodynamical simulation Illustris and follow their galaxies with stellar mass $M_{\star }\ge 1.5\times 10^8{M}_{\odot }$. A median of $\sim 38\%$ of surviving galaxies at $z=0$ are accreted as part of groups and did not infall directly from the field, albeit with significant cluster-to-cluster scatter. The evolution of these galaxy associations is quick, with observational signatures of their common origin eroding rapidly in $1$-$3$ Gyr after infall. Substructure plays a dominant role in fostering the conditions for galaxy mergers to happen, even within the cluster environment. Integrated over time, we identify (per cluster) an average of $17\pm 6$ mergers that occur in infalling galaxy associations, of which $7\pm 3$ occur well within the virial radius of their cluster hosts. The number of mergers show large dispersion from cluster to cluster, with our most massive system having $42$ mergers above our mass cut-off. These mergers, which are typically gas rich for dwarfs and a combination of gas rich and gas poor for $M_{\star }\sim 10^{11}{M}_{\odot }$, may contribute significantly within $\Lambda$CDM to the formation of specific morphologies, such as lenticulars (S0) and blue compact dwarfs in groups and clusters.

12 pages, 11 figures. Accepted for publication in MNRAS

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• Modeling globular clusters in the TNG50 simulation: predictions from dwarfs to giants
• The Effect of Environment on Galaxy Spiral Arms, Bars, Concentration, and Quenching
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• A newly identified galaxy group thanks to tidal streams of intragroup light
• Accretion processes in the galaxy cluster Hydra A/Abell 780
• Is Abell 2261 a fossil galaxy cluster in a transitional dynamical state?