A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with the Lyman Break Technique

Takuji Yamashita, Tohru Nagao, Hiroyuki Ikeda, Yoshiki Toba, Masaru Kajisawa, Yoshiaki Ono, Masayuki Tanaka, Masayuki Akiyama, Yuichi Harikane, Kohei Ichikawa, Toshihiro Kawaguchi, Taiki Kawamuro, Kotaro Kohno, Chien Hsiu Lee, Kianhong Lee, Yoshiki Matsuoka, Mana Niida, Kazuyuki Ogura, Masafusa Onoue, Hisakazu Uchiyama

Research output: Contribution to journalArticlepeer-review

Abstract

We report a discovery of a z = 4.72 radio galaxy, HSC J083913.17+011308.1, using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for Very Large Array Faint Images of the Radio Sky at Twenty centimeter radio sources. The number of known high-z radio galaxies (HzRGs) at z > 3 is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected r-band dropouts with a radio detection, a follow-up optical spectroscopy with the Gemini Multi-Object Spectrographs (GMOS)/Gemini has been performed. The obtained spectrum presents a clear Lyα emission line redshifted to z = 4.72. The spectral energy distribution fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with . The small equivalent width of Lyα and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum, α1400325 of -1.1 and α1400150 of -0.9, demonstrating that the HSC-SSP survey compensates for a subpopulation of HzRGs that are missed in surveys focusing on an ultra-steep spectral index.

Original languageEnglish
Article number60
JournalAstronomical Journal
Volume160
Issue number2
DOIs
Publication statusPublished - 2020 Aug

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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