Abstract
We investigate the nature and evolution of substructure 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 $\delta_b,gal=4.8 1.8$,
$\delta_r,gal=9.5 2.0$ for the blue and red peaks, respectively, and
$\delta_t,gal=7.61.4$ for the entire region. These overdensities
correspond to masses of $M_b = (0.76 0.17) 10^15 h^-1
M_ødot$, $M_r = (2.15 0.32) 10^15 h^-1 M_ødot$, and
$M_t=(3.19 0.40) 10^15 h^-1 M_ødot$ for the red, blue, and
total peaks, respectively. We use the Small MultiDark Planck (SMDPL) simulation
to identify comparably massive $z3$ protoclusters, and uncover the
underlying structure and ultimate fate of the SSA22 protocluster. For this
analysis, we construct mock redshift histograms for each simulated $z3$
protocluster, quantitatively comparing them with the observed SSA22 data. We
find that the observed double-peaked substructure in the SSA22 redshift
histogram corresponds not to a single coalescing cluster, but rather the
proximity of a $10^15h^-1 M_ødot$ protocluster and at least one
$>10^14 h^-1 M_ødot$ 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 $8h^3
Gpc^-3$.
Description
[1709.06572] Understanding substructure in the SSA22 protocluster region using cosmological simulations
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