(Proposal ID) S13A-098

(PI) Toshikawa, Jun

(Proposal Title)
A First Site of Cluster Formation at z~6

(Abstract)
We propose to carry out a deep spectroscopic observation with DEIMOS targeting 
for 43 galaxies in/around the highest-redshift protocluster. In this 
protocluster, at least, eight galaxies are actually clustering at z=6.01 
within the narrow redshift range of Delta z < 0.05. The velocity dispersion of 
the eight protocluster members is 647 km s^-1, which is about three times 
higher than theoretical prediction. This discrepancy could be attributed to 
the distinguishing three-dimensional distribution of the eight protocluster 
members. We have two possible explanations for this discrepancy: either the 
protocluster is already mature, or it is still immature. We would like to 
carry out a deeper and wider observation than previous one. This will 
significantly the number of the confirmed protocluster members and provide 
more accurate three-dimensional structure of the protocluster; this will 
enable us to discriminate two explanations. The wide-field spectroscopy will 
also reveal the relation between the protocluster in formation and its 
surrounding filamentary structure. Through the proposed observation, we can 
approach to the cluster formation history by looking at its primitive 
structure and the relation with large-scale structure.