Galaxy clusters and groups at z~1

However, it is still unclear what keeps some of the high-redshift clusters active in star formation. To address this issue, we performed a multiobject spectroscopic observation of 226 high-redshift (0.8<z<1.3) galaxies in galaxy cluster candidates and the areas surrounding them.

Our spectroscopic observation reveals six to eight clusters/groups at z~0.9 and z~1.3. The redshift measurements demonstrate the reliability of our photometric redshift measurements, which in turn gives credibility for using photometric redshift members for the analysis of large-scale structures (LSSs). Our investigation of the large-scale environment (~10Mpc) surrounding each galaxy cluster reveals LSSs - structures up to ~10Mpc scale - around many of, but not all, the confirmed overdensities and the cluster candidates.