MAHALO Deep Cluster Survey II. Characterizing massive forming galaxies in the Spiderweb protocluster at z = 2.2

Rhythm Shimakawa, Yusei Koyama, Huub J.A. Röttgering, Tadayuki Kodama, Masao Hayashi, Nina A. Hatch, Helmut Dannerbauer, Ichi Tanaka, Ken Ichi Tadaki, Tomoko L. Suzuki, Nao Fukagawa, Zheng Cai, Jaron D. Kurk

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


This paper is the second in a series presenting the results of our deep Hα-line survey towards protoclusters at z > 2, based on narrow-band imaging with the Subaru Telescope. This work investigates massive galaxies in a protocluster region associated with a radio galaxy (PKS 1138 - 262), the Spiderweb galaxy, at z = 2.2. Our 0.5 mag deeper narrow-band imaging than previous surveys collects a total of 68 Hα emitters (HAE). Here, 17 out of the 68 are newly discovered protocluster members. First, a very high characteristic stellar mass of M* = 1011.73 M is measured from a Schechter function fit to the mass distribution of HAEs. Together with the Chandra X-ray data, we find that four out of six massive HAEs (M > 1011 M) show bright X-ray emission, suggesting that they host active galactic nuclei (AGNs). Their mass estimates, therefore, would be affected by the nuclear emission from AGNs. Notably, the X-ray-detected HAEs are likely positioned near the boundary between star-forming and quiescent populations in the rest-frame UVJ plane. Moreover, our deep narrow-band data succeed in probing the bright Hα (+ [N II]) line nebula of the Spiderweb galaxy extending over ~100 physical kpc. These results suggest that the massive galaxies in the Spiderweb protocluster are on the way to becoming the bright red sequence objects seen in local galaxy clusters, where AGNs might play an essential role in their quenching processes, though a more statistical database is needed to build a general picture.

Original languageEnglish
Pages (from-to)5630-5650
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 2018 Dec 1


  • Galaxies: clusters: individual: PKS 1138-262
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift


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