HOLISMOKES. VIII. High-redshift, strong-lens search in the Hyper Suprime-Cam Subaru Strategic Program

TL;DR

This study uses deep neural networks to identify high-redshift strong-lens systems in HSC data, significantly expanding the catalog of such lenses for galaxy evolution research at earlier cosmic times.

Contribution

It introduces two new classifiers trained on diverse datasets, resulting in the largest set of galaxy-scale strong-lens candidates identified in HSC data to date.

Findings

Identified 735 high-quality strong-lens candidates, including 277 new discoveries.

Nearly half of the candidates have lens galaxies with redshifts above 0.6.

The catalog provides valuable targets for upcoming spectroscopic surveys.

Abstract

We carry out a search for strong-lens systems containing high-redshift lens galaxies with the goal of extending strong-lensing-assisted galaxy evolutionary studies to earlier cosmic time. Two strong-lens classifiers are constructed from a deep residual network and trained with datasets of different lens-redshift and brightness distributions. We classify a sample of 5,356,628 pre-selected objects from the Wide-layer fields in the second public data release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) by applying the two classifiers to their HSC $gri$-filter cutouts. Cutting off at thresholds that correspond to a false positive rate of $10^{-3}$ on our test set, the two classifiers identify 5,468 and 6,119 strong-lens candidates. Visually inspecting the cutouts of those candidates results in 735 grade-A or B strong-lens candidates in total, of which 277 candidates are discovered for the first time. This is the single largest set of galaxy-scale strong-lens candidates discovered with HSC data to date, and nearly half of it (331/735) contains lens galaxies with photometric redshifts above 0.6. Our discoveries will serve as a valuable target list for ongoing and scheduled spectroscopic surveys such as the Dark Energy Spectroscopic Instrument, the Subaru Prime Focus Spectrograph project, and the Maunakea Spectroscopic Explorer.