Mock Observations for the CSST Mission: Integral Field Spectrograph--Instrument Simulation

TL;DR

The CSST-IFS is designed to deliver spectro-spatial data over a wide field with high spatial resolution across 350–1000 nm at R≥1000. The paper presents an end-to-end instrument simulator that models the full optical chain (telescope, image slicers, pupil mirrors, slit array, and dual Offner spectrometers) and detector/environmental effects, producing detector-level spectral images from 3D input datacubes via PSF-based propagation and sub-pixel dispersion. The Gehong datacube generator and a suite of calibration simulations (flat, Hg–Ar lamp) plus science targets (e.g., NGC 6217) enable calibration, pipeline validation, and observation planning, with PSF/LSF measurements consistent with design expectations. A three-phase plan—incorporating lab-measured parameters, pre-launch calibration, and post-launch updates—ensures progressive realism and usefulness for mission preparation and scientific analyses.

Abstract

The Chinese Space Station Survey Telescope (CSST) is a next-generation Stage-IV facility renowned for its wide field of view, high image quality, and multi-band observational capabilities. Among the five instruments onboard the CSST, the Integral Field Spectrograph (IFS) offers the unique ability to simultaneously capture spatial and spectral information across a field of view of no less than $6^{''}\times6^{''}$. Key advantages of the IFS include a high spatial resolution of $0.2^{''}$ and a broad spectral coverage from 350 to 1000 nm, making it an ideal instrument for studying physical processes in the vicinity of supermassive black holes within galaxies. To more accurately assess the technical and scientific performance of the CSST-IFS, it is essential to develop a simulation tool that incorporates realistic effects from all optical components. Such a simulation will form an integral part of the CSST-IFS data and pipeline system, enabling the development of the data reduction pipeline well ahead of actual observations. This paper presents an end-to-end simulation workflow for the CSST-IFS, incorporating a wide range of instrumental effects that may influence its spectral and imaging performance. The simulation accounts for optical diffraction effects introduced by all components, such as image slicers and slit array, as well as sub-pixel effects from gratings. It also includes various detector noises, frame-shifting effects, and charge-transfer inefficiency. Real observational conditions--such as target Doppler shift, cosmic rays, and other in-orbit operational effects--are also considered. We describe the technical implementation of the simulation and present results that quantitatively characterize key instrument parameters.

Figures (17)

• Figure 1: Schematic diagram of the optical path of the optical system of CSST.
• Figure 2: Schematic diagram of the optical system of IFS on CSST.
• Figure 3: Schematic diagram of slicer array and pupil-mirror array.
• Figure 4: Flowchart of the IFS spectral imaging simulation process.
• Figure 5: Representative schematic of an imaging spectrometer for IFS instrument simulation.