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 7.4 h ^ { 3 } \mbox { Gpc } ^ { -3 } .