2011MNRAS.415.2670H

We conduct a wide-field narrow-band imaging survey of [O II] emitters in and around the XMMXCS J2215.9-1738 cluster at z= 1.46 with Subaru/Suprime-Cam. In a 32 {x} 23 arcmin2 area, we select 380 [O II] emitting galaxies down to 1.4 {x} 10^–17 erg/s/cm2. Among them, 16 [O II] emitters in the central region of the cluster are confirmed by near-infrared spectroscopy with Subaru/MOIRCS, suggesting that our photometric selection is valid for sample [O II] emitters at z= 1.46. We find that [O II] emitters are distributed along filamentary large-scale structures around the cluster, which are among the largest structures of star-forming galaxies ever identified at 1.3 ≲ z ≲ 3.0. We define several environments such as cluster core, outskirts, filament and field in order to investigate the environment dependence of star-forming galaxies at z= 1.46. The colour–magnitude diagram of z'-K versus K for the [O II] emitting galaxies shows that a significantly higher fraction of [O II] emitters with red z'-K colours is seen in the cluster core than in other environments. It seems that the environment that hosts such red star-forming galaxies shifts from the core region at z= 1.46 to the outskirts of clusters at lower redshifts. A multicolour analysis of the red emitters indicates that these galaxies are more like nearly passively evolving galaxies which host [O II] emitting active galactic nuclei (AGNs), rather than dust-reddened star-forming [O II] emitters. We argue therefore that AGN feedback may be one of the critical processes to quench star formation in massive galaxies in high-density regions. The emission line ratios of [O III]/Hβ and [N II]/Hα of the [O II] emitters in the cluster core support the inference that there is a moderate contribution of AGN to the emitters. We also find that the cluster has experienced high star formation activities at rates comparable to that in the field at z= 1.46 in contrast to lower redshift clusters, and that star formation activity in galaxy clusters on average increases with redshift up to z= 1.46. In addition, line ratios of [N II]/Hα and [O III]/Hβ indicate that a mass–metallicity relation exists in the cluster at z= 1.46, which is similar to that of star-forming galaxies in the field at z ∼ 2. These results all suggest that at z ∼ 1.5 star formation activity in the cluster core becomes as high as those in low-density environments and that there is apparently not yet a strong environmental dependence, except for the red emitters.