Cosmo-Paleontology: Statistics of Fossil Groups in a Gravity-Only
  Simulation
  We present a detailed study of fossil group candidates identified in "Last
Journey", a gravity-only cosmological simulation covering a $(3.4\,
h^{-1}\mathrm{Gpc})^3$ volume with a particle mass resolution of $m_p \approx
2.7 \times 10^9\, h^{-1}\mathrm{M}_\odot$. The simulation allows us to
simultaneously capture a large number of group-scale halos and to resolve their
internal structure. Historically, fossil groups have been characterized by high
X-ray brightness and a large luminosity gap between the brightest and second
brightest galaxy in the group. In order to identify candidate halos that host
fossil groups, we use halo merger tree information to introduce two parameters:
a luminous merger mass threshold ($M_\mathrm{LM}$) and a last luminous merger
redshift cut-off ($z_\mathrm{LLM}$). The final parameter choices are informed
by observational data and allow us to identify a plausible fossil group sample
from the simulation. The candidate halos are characterized by reduced
substructure and are therefore less likely to host bright galaxies beyond the
brightest central galaxy. We carry out detailed studies of this sample,
including analysis of halo properties and clustering. We find that our simple
assumptions lead to fossil group candidates that form early, have higher
concentrations, and are more relaxed compared to other halos in the same mass
range.
