Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with Lyman Break Technique. (arXiv:2006.04844v1 [astro-ph.GA])

Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with Lyman Break Technique. (arXiv:2006.04844v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yamashita_T/0/1/0/all/0/1">Takuji Yamashita</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nagao_T/0/1/0/all/0/1">Tohru Nagao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ikeda_H/0/1/0/all/0/1">Hiroyuki Ikeda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toba_Y/0/1/0/all/0/1">Yoshiki Toba</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kajisawa_M/0/1/0/all/0/1">Masaru Kajisawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ono_Y/0/1/0/all/0/1">Yoshiaki Ono</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tanaka_M/0/1/0/all/0/1">Masayuki Tanaka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Akiyama_M/0/1/0/all/0/1">Masayuki Akiyama</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harikane_Y/0/1/0/all/0/1">Yuichi Harikane</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ichikawa_K/0/1/0/all/0/1">Kohei Ichikawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kawaguchi_T/0/1/0/all/0/1">Toshihiro Kawaguchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kawamuro_T/0/1/0/all/0/1">Taiki Kawamuro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kohno_K/0/1/0/all/0/1">Kotaro Kohno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_C/0/1/0/all/0/1">Chien-Hsiu Lee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_K/0/1/0/all/0/1">Kianhong Lee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matsuoka_Y/0/1/0/all/0/1">Yoshiki Matsuoka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Niida_M/0/1/0/all/0/1">Mana Niida</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ogura_K/0/1/0/all/0/1">Kazuyuki Ogura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Onoue_M/0/1/0/all/0/1">Masafusa Onoue</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Uchiyama_H/0/1/0/all/0/1">Hisakazu Uchiyama</a>

We report a discovery of $z = 4.72$ radio galaxy, HSC J083913.17+011308.1, by
using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic
Survey (HSC-SSP) catalog for VLA FIRST 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 GMOS/Gemini has been performed. The
obtained spectrum presents a clear Ly$alpha$ emission line redshifted to
$z=4.72$. The SED fitting analysis with the rest-frame UV and optical
photometries suggests the massive nature of this HzRG with $log{M_*/M_{odot}}
= 11.4$. The small equivalent width of Ly$alpha$ 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: $alpha^{325}_{1400}$ of $-1.1$ and $alpha^{150}_{1400}$ of $-0.9$,
demonstrating that the HSC-SSP survey compensates for a sub-population of HzRGs
which are missed in surveys focusing on an ultra-steep spectral index.

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