Properties of star-forming galaxies in a cluster and its surrounding structure at

Abstract

We conduct a wide-field narrow-band imaging survey of [Oii] emitters in and around the XMMXCS J2215.9-1738 cluster at z= 1.46 with Subaru/Suprime-Cam. In a 32 × 23arcmin2 area, we select 380 [Oii] emitting galaxies down to 1.4 × 10-17ergs-1 cm-2. Among them, 16 [Oii] 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 [Oii] emitters at z= 1.46. We find that [Oii] 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 [Oii] emitting galaxies shows that a significantly higher fraction of [Oii] 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 [Oii] emitting active galactic nuclei (AGNs), rather than dust-reddened star-forming [Oii] 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 [Oiii]/Hβ and [Nii]/Hα of the [Oii] 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 [Nii]/Hα and [Oiii]/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. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.