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Mock Observations for the CSST Mission: Main Surveys--An Overview of Framework and Simulation Suite

Cheng-Liang Wei, Guo-Liang Li, Yue-Dong Fang, Xin Zhang, Yu Luo, Hao Tian, De-Zi Liu, Xian-Ming Meng, Zhang Ban, Xiao-Bo Li, Zun Luo, Jing-Tian Xian, Wei Wang, Xi-Yan Peng, Nan Li, Ran Li, Li Shao, Tian-Meng Zhang, Jing Tang, Yang Chen, Zhao-Xiang Qi, Zi-Huang Cao, Huan- Yuan Shan, Lin Nie, Lei Wang, Zizhao He, Rui-Biao Luo, Quan-Yu Liu, Zhao-Jun Yan

TL;DR

This work presents a high-fidelity, GalSim-based simulation framework for the CSST main survey that generates pixel-level mock imaging and slitless-spectroscopic data using realistic ground-truth catalogs (Stellar, Galaxy, Quasar) and detailed instrument models (PSF, field distortion, noise, and detector effects). It outlines a modular, per-chip workflow with four-band imaging and 24-grating slitless spectroscopy, including bidirectional dispersion and a robust interpolation scheme for PSF across the field. The paper also describes the Cycle-9 data release, comprising 2,442 exposures over ~50 deg^2 with 73,260 detector files, and demonstrates validation against input catalogs with >95% recovery at SNR>5 and faithful color-magnitude behavior. The framework supports instrument optimization, calibration strategy testing, and science-case development, with planned Cycle-10 expansions and public availability to the community.

Abstract

The Chinese Space Station Survey Telescope (CSST) is a flagship space-based observatory. Its main survey camera is designed to conduct high spatial resolution near-ultraviolet to near-infrared imaging and low-resolution spectroscopic surveys. To maximize the scientific output of CSST, we have developed a comprehensive, high-fidelity simulation pipeline for reproducing both imaging and spectroscopic observations. This paper presents an overview of the simulation framework, detailing its implementation and components. Built upon the GalSim package and incorporating the latest CSST instrumental specifications, our pipeline generates pixel-level mock observations that closely replicate the expected instrumental and observational conditions. The simulation suite integrates realistic astrophysical object catalogs, instrumental effects, point spread function (PSF) modeling, and observational noises to produce accurate synthetic data. We describe the key processing stages of the simulation, from constructing the input object catalogs to modeling the telescope optics and detector responses. Furthermore, we introduce the most recent release of simulated datasets, which provide a crucial testbed for data processing pipeline developments, calibration strategies, and scientific analyses, ensuring that CSST will meet its stringent requirements. Our pipeline serves as a vital tool for optimizing CSST main survey strategies and ensuring robust cosmological measurements.

Mock Observations for the CSST Mission: Main Surveys--An Overview of Framework and Simulation Suite

TL;DR

This work presents a high-fidelity, GalSim-based simulation framework for the CSST main survey that generates pixel-level mock imaging and slitless-spectroscopic data using realistic ground-truth catalogs (Stellar, Galaxy, Quasar) and detailed instrument models (PSF, field distortion, noise, and detector effects). It outlines a modular, per-chip workflow with four-band imaging and 24-grating slitless spectroscopy, including bidirectional dispersion and a robust interpolation scheme for PSF across the field. The paper also describes the Cycle-9 data release, comprising 2,442 exposures over ~50 deg^2 with 73,260 detector files, and demonstrates validation against input catalogs with >95% recovery at SNR>5 and faithful color-magnitude behavior. The framework supports instrument optimization, calibration strategy testing, and science-case development, with planned Cycle-10 expansions and public availability to the community.

Abstract

The Chinese Space Station Survey Telescope (CSST) is a flagship space-based observatory. Its main survey camera is designed to conduct high spatial resolution near-ultraviolet to near-infrared imaging and low-resolution spectroscopic surveys. To maximize the scientific output of CSST, we have developed a comprehensive, high-fidelity simulation pipeline for reproducing both imaging and spectroscopic observations. This paper presents an overview of the simulation framework, detailing its implementation and components. Built upon the GalSim package and incorporating the latest CSST instrumental specifications, our pipeline generates pixel-level mock observations that closely replicate the expected instrumental and observational conditions. The simulation suite integrates realistic astrophysical object catalogs, instrumental effects, point spread function (PSF) modeling, and observational noises to produce accurate synthetic data. We describe the key processing stages of the simulation, from constructing the input object catalogs to modeling the telescope optics and detector responses. Furthermore, we introduce the most recent release of simulated datasets, which provide a crucial testbed for data processing pipeline developments, calibration strategies, and scientific analyses, ensuring that CSST will meet its stringent requirements. Our pipeline serves as a vital tool for optimizing CSST main survey strategies and ensuring robust cosmological measurements.

Paper Structure

This paper contains 37 sections, 20 equations, 22 figures, 1 table.

Table of Contents

  1. Introduction
  2. Mission Overview
  3. The True Universe
  4. Stellar Catalogues
  5. Galaxy Catalogues
  6. Jiu-Tian cosmological simulation
  7. Semi-analytical modeling
  8. Weak lensing distortions
  9. The Simulation Workflow
  10. Multi-band Imaging Observation
  11. Slitless Spectroscopic Observation
  12. Simulation Orchestration
  13. The Simulation Suite
  14. Point-spread Function
  15. System-level PSF Simulation
  16. ...and 22 more sections

Figures (22)

  • Figure 1: The arrangement of the currently planed scientific instrument terminals for CSST mission.
  • Figure 2: Response curves of the CSST passbands, accounting for the combined efficiencies of the mirrors, filters, and detector quantum efficiency (QE). The vertical dashed lines indicate the specific wavelengths at which the PSFs are sampled in our simulation.
  • Figure 3: Focal plane layout of the CSST main survey camera (SCam). The array consists of 30 detectors arranged in a 6 × 5 grid, with each detector equipped with either a filter or a filter combined with a grism. The central detectors are dedicated to photometric observations across the NUV, u, g, r, i, z, and y bands, while the detectors along the edges are assigned to spectroscopic observations in the GU, GV, and GI bands. The shutter opens along the x-axis.
  • Figure 4: The distribution in the Kiel Diagram of the stars in the output catalog.
  • Figure 5: The evolution of stellar mass functions from $z=0$ to 2. The blue symbols are the observation data from Henriques+2015MNRAS.
  • ...and 17 more figures