CSST Strong Lensing Preparation: Forecast the galaxy-galaxy strong lensing population for the China Space Station Telescope

Kavli Affiliate: Hu Zhan

| First 5 Authors: Xiaoyue Cao, Ran Li, Nan Li, Rui Li, Yun Chen

| Summary:

Galaxy-galaxy strong gravitational lens (GGSL) is a powerful probe for the
formation and evolution of galaxies and cosmology, while the sample size of
GGSLs leads to considerable uncertainties and potential bias. The China Space
Station Telescope (CSST, planned to be launched in 2025) will conduct
observations across 17,500 square degrees of the sky, capturing images in the
$ugriz$ bands with a spatial resolution comparable to that of the Hubble Space
Telescope (HST). We ran a set of Monte Carlo simulations to predict that the
CSST’s wide-field survey will observe $sim$160,000 galaxy-galaxy strong lenses
over the lifespan, expanding the number of existing galaxy-galaxy lens samples
by three orders of magnitude, which is comparable to the Euclid telescope
launched during the same period but with additional color information.
Specifically, the CSST can detect strong lenses with Einstein radii above
$0.64pm0.42$ arcsec, corresponding to the velocity dispersions of $217.19 pm
50.55 , text{km/s}$. These lenses exhibit a median magnification of $sim$5.
The apparent magnitude of the unlensed source in the g-band is $25.87 pm
1.19$. The signal-to-noise ratio of the lensed images covers a range of $sim
20$ to $sim 1000$, allowing us to determine the Einstein radius with an
accuracy ranging from $sim 1 %$ to $sim 0.1 %$, ignoring various modeling
systematics. Besides, our estimations show that CSST can observe uncommon
systems, such as double source-plane and spiral galaxy lenses. The above
selection functions of the CSST strong lensing observation help optimize the
strategy of finding and modeling GGSLs.

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