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

Authors

  • Masao Hayashi,

    Corresponding author
    1. Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan
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  • Tadayuki Kodama,

    1. Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan
    2. Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720, USA
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  • Yusei Koyama,

    1. Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan
    2. Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
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  • Ken-ichi Tadaki,

    1. Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan
    2. Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
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  • Ichi Tanaka

    1. Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720, USA
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E-mail: masao.hayashi@nao.ac.jp

ABSTRACT

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 × 23 arcmin2 area, we select 380 [O ii] emitting galaxies down to 1.4 × 10−17 erg s−1 cm−2. 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.

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