Mock Observations for the CSST Mission: Main Surveys -- the Mock Catalogue

TL;DR

The paper presents a comprehensive mock catalogue for the CSST main survey, integrating Milky Way stars (Galaxia or TRILEGAL), a JT1G-based dark matter light-cone populated via a semi-analytical model, and full-sky weak-lensing maps from multi-plane ray-tracing. It computes land-use-ready photometry by convolving SEDs (STARDUSTER PCA) with CSST throughputs and assigns quasar SEDs (SIMQSO) to galaxies, yielding a dataset with positions, redshifts, masses, shapes, sizes, SEDs, lensing shears, and magnifications out to $z\sim3.5$. The catalogue is validated against observational constraints and theoretical models, showing good agreement for stellar mass–halo mass relations, mass functions, and weak-lensing power spectra, while acknowledging Planck-based cosmology offsets in $S_8$ and areas for refinement. Overall, the mock catalogue provides a robust, flexible resource for CSST image simulation, pipeline development, and cosmological analyses of galaxy clustering and weak lensing, with clear paths for incorporating additional morphologies and orientation-sensitive SEDs in future work.

Abstract

The Chinese Space Station Survey Telescope (CSST) is a flagship space mission, designed to carry out a large-area sky survey to explore the nature of dark matter and dark energy in the Universe. The onboard multi-band imaging and slitless spectroscopic modules will enable us to obtain photometric data for billions of galaxies and stars, as well as hundreds of millions of spectroscopic measurements, advancing various scientific analyses such as galaxy clustering and weak gravitational lensing. To support the image simulations for the main survey of the CSST mission, we present a mock catalogue of stars and galaxies. For stars, the mock catalogue is generated using either Galaxia or TRILEGAL, both of which provide a range of stellar properties to meet the requirements of CSST image simulations. For galaxies, we built a mock light-cone up to redshift z~3.5 from the cosmological Nbody simulation and populated the mock galaxy catalogue from the dark mater haloes using a semi-analytical galaxy formation model. We then performed a full-sky ray-tracing simulation of weak gravitational lensing to obtain lensing shear at the position of each galaxy in the light-cone. To support both multi-band imaging and slitless spectroscopic simulations, we computed the spectral energy distribution (SED) for each galaxy based on its star formation history using a supervised deep-learning model and determined the magnitudes in each band using the CSST throughputs. Finally, the properties of our mock galaxies include positions, redshifts, stellar masses, shapes, sizes, SEDs, lensing shears and magnifications. We have validated our mock catalogue against observational data and theoretical models, with results showing good overall agreement. The catalogue provides a flexible dataset for the development of CSST image processing and can support a wide range of cosmological analyses within the CSST mission.

Figures (19)

• Figure 1: An overview of the pipline for the input mock catalogue.
• Figure 2: The density distribution of the field stars around the direction of $(\alpha, \delta)=(270^\circ, 67^\circ)$.
• Figure 3: In the top panel, we show a sky region of $\sim 13$${\rm deg}^2$ from the full-sky galaxy light-cone. The middle and bottom panels illustrate the distribution of mock galaxies and dark matter density fields, respectively, at redshifts of 0.5, 1.0, 2.0 and 3.0, where the filaments of large-scale structure can be clearly distinguished in detail.
• Figure 4: The mass-size relation of spiral galaxies and elliptical galaxies at $z=2$ to $z=0$ adopted in our mock galaxies catalogue. The dashed line indicates the $1\sigma$ scatter of the galaxy size, $R_{50}$.
• Figure 5: The relative deviation between the recovered SEDs and the SEDs of the original output of 10,000 galaxies at $z=0,1,2$.