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arXiv · 2106.13807

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XIV. A Candidate Type-II Quasar at z=6.1292

Masafusa Onoue·Yoshiki Matsuoka·Nobunari Kashikawa·Michael A. Strauss·Kazushi Iwasawa·Takuma Izumi·Tohru Nagao·Naoko Asami·Seiji Fujimoto·Yuichi Harikane·Takuya Hashimoto·Masatoshi Imanishi·Chien-Hsiu Lee·Takatoshi·Shibuya·Yoshiki Toba
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Abstract

We present deep Keck/MOSFIRE near-infrared spectroscopy of a strong Lyman alpha emitting source at z=6.1292, HSC J142331.71-001809.1, which was discovered by the SHELLQS program from imaging data of the Subaru Hyper Suprime-Cam (HSC) survey. This source is one of five objects that show unresolved (<230 km s-1) and prominent (>10^44 erg s-1) Lyman alpha emission lines at absolute 1450 angstrom continuum magnitudes of M1450~-22 mag. Its rest-frame Lyman alpha equivalent width (EW) is 370+/-30 angstrom. In the 2 hour Keck/MOSFIRE spectrum in Y band, the high-ionization CIV 1548,1550 doublet emission line was clearly detected with FWHM =120+/-20 km s-1 and a total rest-frame EW of 37-5+6 angstrom. We also report the detection of weak continuum emission, and the tentative detection of OIII] 1661,1666 in the 4 hour J band spectrum. Judging from the UV magnitude, line widths, luminosities, and EWs of Lyman alpha and CIV, we suggest that this source is a reionization-era analog of classical type-II AGNs, although there is a possibility that it represents a new population of AGN/galaxy composite objects in the early universe. We compare the properties of J1423-0018 to intermediate-redshift type-II AGNs and CIV emitters seen in z=6-7 galaxy samples. Further observations of other metal emission lines in the rest-frame UV or optical, and X-ray follow-up observations of the z=6-7 narrow-line quasars are needed for more robust diagnostics and to determine their nature.

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Masafusa Onoue, Yoshiki Matsuoka, Nobunari Kashikawa, Michael A. Strauss, Kazushi Iwasawa, Takuma Izumi, Tohru Nagao, Naoko Asami, Seiji Fujimoto, Yuichi Harikane, Takuya Hashimoto, Masatoshi Imanishi, Chien-Hsiu Lee, Takatoshi, Shibuya, Yoshiki Toba. 2021-06-25. Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XIV. A Candidate Type-II Quasar at z=6.1292. https://doi.org/10.3847/1538-4357%2Fac0f07

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