Discovery of an unusually compact lensed Lyman-break galaxy from the Hyper Suprime-Cam Survey. Issue 3 (28th February 2020)

• Record Type: Journal Article
• Authors: Jaelani, Anton T; More, Anupreeta; Sonnenfeld, Alessandro; Oguri, Masamune; Rusu, Cristian E; Wong, Kenneth C; Chan, James H H; Suyu, Sherry H; Kayo, Issha; Lee, Chien-Hsiu; Inoue, Kaiki T
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 494:Issue 3(2020)
• Page Start: 3156
• Page End: 3165
• Publication Date: 2020-02-28
• Subjects: gravitational lensing: strong -- galaxies: high-redshift; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa583
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We report the serendipitous discovery of HSC J0904–0102, a quadruply lensed Lyman-break galaxy (LBG) in the Survey of Gravitationally-lensed Objects in Hyper Suprime-Cam Imaging (SuGOHI). Owing to its point-like appearance, the source was thought to be a lensed active galactic nucleus. We obtained follow-up spectroscopic data with the Gemini Multi-Object Spectrographs on the Gemini South Telescope, which confirmed this to be a lens system. The deflecting foreground galaxy is a typical early-type galaxy at a high redshift of $z_{\ell}=0.957$ with stellar velocity dispersion $\sigma_v=259\pm56$ km s −1 . The lensed source is identified as an LBG at $z_{\rm s}=3.403$, based on the sharp drop bluewards of Ly α and other absorption features. A simple lens mass model for the system, assuming a singular isothermal ellipsoid, yields an Einstein radius of $\theta_{\rm Ein}=1.23$ arcsec and a total mass within the Einstein radius of $M_{\rm Ein}=(5.55\pm0.24)\times10^{11}\rm M_{\odot}$ corresponding to a velocity dispersion of $\sigma_{\rm SIE}=283\pm3$ km s −1, which is in good agreement with the value derived spectroscopically. The most isolated lensed LBG image has a magnification of $\sim 6.5$ . In comparison with other lensed LBGs and typical $z\sim4$ LBG populations, HSC J0904–0102 is unusually compact, an outlier at $>2\sigma$ confidence. Together with a previously discovered SuGOHI lens, HSC J1152+0047, which is similarly compact, we believe that the HSC survey is extending LBG studies down to smaller galaxy sizes.