Understanding large-scale structure in the SSA22 protocluster region
  using cosmological simulations
  We investigate the nature and evolution of large-scale structure within the
SSA22 protocluster region at $z=3.09$ using cosmological simulations. A
redshift histogram constructed from current spectroscopic observations of the
SSA22 protocluster reveals two separate peaks at $z = 3.065$ (blue) and $z =
3.095$ (red). Based on these data, we report updated overdensity and mass
calculations for the SSA22 protocluster. We find $\delta_{b,gal}=4.8 \pm 1.8$,
$\delta_{r,gal}=9.5 \pm 2.0$ for the blue and red peaks, respectively, and
$\delta_{t,gal}=7.6\pm 1.4$ for the entire region. These overdensities
correspond to masses of $M_b = (0.76 \pm 0.17) \times 10^{15} h^{-1}
M_{\odot}$, $M_r = (2.15 \pm 0.32) \times 10^{15} h^{-1} M_{\odot}$, and
$M_t=(3.19 \pm 0.40) \times 10^{15} h^{-1} M_{\odot}$ for the red, blue, and
total peaks, respectively. We use the Small MultiDark Planck (SMDPL) simulation
to identify comparably massive $z\sim 3$ protoclusters, and uncover the
underlying structure and ultimate fate of the SSA22 protocluster. For this
analysis, we construct mock redshift histograms for each simulated $z\sim 3$
protocluster, quantitatively comparing them with the observed SSA22 data. We
find that the observed double-peaked structure in the SSA22 redshift histogram
corresponds not to a single coalescing cluster, but rather the proximity of a
$\sim 10^{15}h^{-1} M_{\odot}$ protocluster and at least one $>10^{14} h^{-1}
M_{\odot}$ cluster progenitor. Such associations in the SMDPL simulation are
easily understood within the framework of hierarchical clustering of dark
matter halos. We finally find that the opportunity to observe such a phenomenon
is incredibly rare, with an occurrence rate of $7.4h^3 \mbox{ Gpc}^{-3}$.
