Title: Discovering Strongly Lensed Quasar Candidates with Catalogue-Based Methods from DESI Legacy Surveys

Speaker: Zichao He (National Astronomical Observatories, Chinese Academy of Sciences)

Time: 10:00am, February 21, 2023

Location: 5-516, PMO Xianlin Campus

Abstract: The Hubble tension, revealed by a ～5σ discrepancy between measurements of the Hubble-Lemaitre constant from early- and local-Universe observations, is one of the most significant problems in modern cosmology. In order to better understand the origin of this mismatch, independent techniques to measure H0, such as strong lensing time delays, are required. Notably, the sample size of such systems is key to minimising statistical uncertainties and cosmic variance, which can be improved by exploring the datasets of large-scale sky surveys like DESI (Dark Energy Spectroscopic Instrument). We identify possible strong lensing time-delay systems within DESI by selecting candidate multiply imaged lensed quasars from a catalogue of 24,440,816 candidate QSOs contained in the 9th data release of the DESI Legacy Imaging Surveys (DESI-LS). We identify 620 new candidate multiply imaged lensed quasars (101 Grade-A, 214 Grade-B, 305 Grade-C). This number excludes 53 known spectroscopically confirmed systems and existing candidate systems identified in other similar catalogues. When available, these new candidates will be further checked by combining the spectroscopic and photometric data from DESI. In this talk, I will introduce the methodologies that have been developed to achieve such a catalogue and the potential applications of it to other data-sets, such as KiDS and CSST.