We present a discovery of definitive large-scale structures around RXJ0152.7–1352 at z = 0.83 based on spectroscopic redshifts .
In our previous papers , we reported a photometric identification of the large-scale structures at z \sim 0.8 .
A spectroscopic follow-up observation was carried out on 8 selected regions covering the most prominent structures to confirm their association to the main cluster .
In six out of the eight fields , a well isolated peak is identified in the distribution of spectroscopic redshifts at or near the cluster redshift .
This is strong evidence for the presence of large-scale structures associated to the main cluster at z = 0.83 .
It seems that there are two large filaments of galaxies at z \sim 0.837 and z \sim 0.844 crossing in this field .
We then investigate stellar populations of galaxies in the structures .
The composite spectra are constructed from a number of red member galaxies on the colour-magnitude sequence .
We consider three representative environments – cluster , group , and field – to investigate the environmental dependence of their star formation histories .
We quantify the strengths of the 4000 \AA break ( D _ { 4000 } ) and the H \delta absorption features and compare them with model predictions .
The “ cluster ” red galaxies do not show any sign of on-going or recent star formation activities and the passive evolution can naturally link them to the present-day red sequence galaxies in the Sloan Digital Sky Survey .
In contrast , the red galaxies in “ groups ” and in the “ field ” tend to show signs of remaining and/or recent star formation activities characterized by weak [ OII ] emissions and/or strong H \delta absorptions .
Our current data seem to favour a scenario that star formation is truncated in a short time scale ( < 1Gyr ) .
This would imply that galaxy-galaxy interactions are responsible for the truncation of star formation .