CSST Strong Lensing Preparation: Cosmological constraints from double-source-plane strong lensing systems in era of CSST
Bei-Chen Wu, Xiaoyue Cao, Nan Li, Yan Gong, Shenzhe Cui, Di Wu, Tong Zhao, Junhui Yan
TL;DR
This work forecasts cosmological constraints from double source plane lensing (DSPL) using CSST-style simulations, exploring how survey depth (WF/DF/UDF) and the Einstein-radius ratio $β^{-1}$ affect inference in a flat $w$CDM universe. By modeling DSPLs with SIE lenses and Sérsic sources and performing Bayesian inference on mock CSST data, the study finds that deeper UDF observations and larger $β^{-1}$ yield substantially tighter constraints on $w$ and $Ω_m$, with smaller $β$ improving precision further. While results are idealized, they demonstrate the potential of CSST DSPLs to beat previous DSPL constraints (e.g., the Jackpot system) and highlight the importance of careful DSPL system selection, redshift accuracy, and future hierarchical analyses across large samples. The authors also discuss the broader context of combining DSPLs with other probes and facilities to maximize cosmological leverage in the coming era of large-scale surveys.
Abstract
Double source plane strong lensing (DSPL) systems offer a robust, independent probe of cosmological parameters. The Chinese Space Station Telescope (CSST) is expected to discover hundreds of DSPLs, yet the survey modes and system configurations that best enable cosmological inference remain uncertain. To investigate the impact of varying signal-to-noise ratios (SNR) and Einstein radius ratios of DSPLs (denoted as $β^{-1}$ parameters) on cosmographic inference under different CSST survey modes (Wide Field (WF), Deep Field (DF), and Ultra-Deep Field (UDF)), we simulate and model mock lenses with Singular Isothermal Ellipsoid (SIE) mass profiles and Sérsic sources whose image properties are tailored to CSST specifications. Assuming a flat $w$CDM universe with fiducial values $Ω_{\rm m} = 0.30966$ and $w = -1$, and uniform priors of $Ω_{\rm m} \in [0, 1]$ and $w \in [-2, -1/3$), we find that the constraining power on cosmological parameters for a given DSPL system increases significantly with survey depth. For a representative DSPL system with two prominent arcs and a moderate $β^{-1}=1.17$, the constraints on ($w, Ω_{\rm m}$) improve from ($-1.28_{-1.00}^{+0.64}, 0.50_{-0.32}^{+0.28}$) in the WF to ($-1.59_{-0.32}^{+0.63}, 0.42_{-0.06}^{+0.15}$) in the UDF. Furthermore, we find that systems with smaller $β$ values yield tighter cosmographic constraints. We conclude that DSPL systems identified in UDF observations, particularly those with small $β$, are the most promising candidates for early-stage cosmological studies with CSST.