Forecasting the E_G measurements from the photometric and spectroscopic surveys of Chinese Space Station Survey Telescope (CSST)

Abstract

We present forecasts for the $E_G$ statistic using redshift distributions of realistic mock galaxy samples from the upcoming Chinese Space Station Survey Telescope (CSST). The dominant uncertainty in $E_G$ stems from the redshift space distortion parameter ${\beta}$, whose precision limits the overall constraining power. Our analysis shows that CSST will nevertheless achieve $E_G$ constraints at the few-percent level (3%-9%) over $0 < z < 1.2$, an improvement by a factor of several to an order of magnitude over current observations. Within the $\mu-\Sigma$ modified gravity framework, the parameter $\Sigma_0$, associated with the effective gravitational constant of the Weyl potential, can be constrained to $\sim 5\%$ precision. In a plausible scenario where upcoming spectroscopic surveys determine ${\beta}$ to 1\% accuracy, $E_G$ constraints tighten to the percent level, and $\Sigma_0$ becomes measurable at $\sim 1\%$. These results demonstrate that CSST will serve as a powerful facility for testing gravity and underscore the essential synergy between photometric weak lensing and spectroscopic surveys in probing cosmic acceleration.