Survey of Gravitationally lensed Objects in HSC Imaging (SuGOHI)

IV. Lensed quasar search in the HSC survey

¹ Institute of Physics, Laboratory of Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
e-mail: hung-hsu.chan@epfl.ch
² Department of Physics, National Taiwan University, 10617 Taipei, Taiwan
³ Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), 11F of ASMAB, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
⁴ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
⁵ Physik-Department, Technische Universität München, James-Franck-Strae 1, 85748 Garching, Germany
⁶ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁷ Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
⁸ Department of Physics, Kindai University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
⁹ Astronomical Institute, Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan
¹⁰ Astronomy Study Program and Bosscha Observatory, FMIPA, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132, Indonesia
¹¹ The Inter-University Center for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune 411007, India
¹² Department of Physics, Faculty of Science, Kyoto Sangyo University, 603-8555 Kyoto, Japan
¹³ Department of Astronomy, University of Geneva, ch. d’Écogia 16, 1290 Versoix, Switzerland
¹⁴ NSF’s National Optical-Infrared Astronomy Laboratory, 950 N Cherry Ave, Tucson, AZ 85719, USA
¹⁵ Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁶ Research Center for the Early Universe, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁷ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

Received: 31 October 2019
Accepted: 31 January 2020

Abstract

Strong gravitationally lensed quasars provide a powerful means to study galaxy evolution and cosmology. We use CHITAH, which is an algorithm used to hunt for new lens systems, particularly lensed quasars, in the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) S16A. We present 46 lens candidates, of which 3 are previously known. We select four high-grade candidates from CHITAH for spectroscopic follow-up observations, and include two additional lenses found by YATTALENS, an algorithm used to classify lensed galaxies. We obtain X-shooter spectra of these six promising candidates for lens confirmation and redshift measurements. We report new spectroscopic redshift measurements for both the lens and source galaxies in four lens systems. We apply the lens modeling software GLEE to model our six X-shooter lenses uniformly. Through our analysis of the HSC images, we find that HSCJ022622−042522, HSCJ115252+004733, and HSCJ141136−010216 have point-like lensed images, and that the lens light distribution is well aligned with the lens mass distribution within 6 deg. We estimate the fluxes of the lensed source emission lines using X-shooter spectra, and use line ratio as a diagnostic on the Baldwin-Phillips-Terlevich (BPT) diagram. As a result, we find that HSCJ022622−042522 has a probable quasar source based on the upper limit of the [N II] flux intensity. We also measure the FWHM of Lyα emission of HSCJ141136−010216 to be ∼233 km s⁻¹, showing that it is a probable Lyman-α emitter.