# Cosmology from the Chinese Space Station Optical Survey (CSS-OS)

## TL;DR

The CSS-OS survey will significantly improve constraints on dark matter and dark energy by combining weak lensing and galaxy clustering data, surpassing current surveys in precision.

## Contribution

This work presents the first detailed forecast of cosmological constraints from CSS-OS, including systematics and joint analyses, highlighting its potential for cosmology.

## Key findings

- CSS-OS can improve cosmological parameter constraints by up to an order of magnitude.
- Joint analysis of WL, galaxy clustering, and galaxy-galaxy lensing enhances constraints.
- Systematic effects are considered, providing realistic forecasts.

## Abstract

The Chinese Space Station Optical Survey (CSS-OS) is a planned full sky survey operated by the Chinese Space Station Telescope (CSST). It can simultaneously perform the photometric imaging and spectroscopic slitless surveys, and will probe weak and strong gravitational lensing, galaxy clustering, individual galaxies and galaxy clusters, active galactic nucleus (AGNs), and so on. It aims to explore the properties of dark matter and dark energy and other important cosmological problems. In this work, we focus on two main CSS-OS scientific goals, i.e. the weak gravitational lensing (WL) and galaxy clustering surveys. We generate the mock CSS-OS data based on the observational COSMOS and zCOSMOS catalogs. We investigate the constraints on the cosmological parameters from the CSS-OS using the Markov Chain Monte Carlo (MCMC) method. The intrinsic alignments, galaxy bias, velocity dispersion, and systematics from instrumental effects in the CSST WL and galaxy clustering surveys are also included, and their impacts on the constraint results are discussed. We find that the CSS-OS can improve the constraints on the cosmological parameters by a factor of a few (even one order of magnitude in the optimistic case), compared to the current WL and galaxy clustering surveys. The constraints can be further enhanced when performing joint analysis with the WL, galaxy clustering, and galaxy-galaxy lensing data. Therefore, the CSS-OS is expected to be a powerful survey for exploring the Universe. Since some assumptions may be still optimistic and simple, it is possible that the results from the real survey could be worse. We will study these issues in details with the help of simulations in the future.