CSST Strong Lensing Preparation: Forecasting 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 lensing (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, to be launched in late 2026) 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. 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 its
lifespan, increasing the number of existing galaxy-galaxy strong lens samples
by three orders of magnitude. This is comparable to the capabilities of the
$it Euclid$ telescope but with the added benefit of additional color
information. Specifically, the CSST can detect strong lenses with Einstein
radii about $0.64pm0.42^{"}$, 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 sources 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. Our estimates indicate that CSST can observe rare systems
like 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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