Mock Observations for the CSST Mission: Multi-Channel Imager--The Cluster Field

TL;DR

This work provides a comprehensive end-to-end simulation framework for the CSST-MCI cluster field, enabling realistic assessment of strong and weak lensing analyses. It combines a CosmoDC2-based mock cluster with a main $N$-body halo modeled as $M_{\rm vir}=1.13\times10^{15}\,M_{\odot}$ at $z_{\rm L}=0.3$ and PIEMD subhalos, and ray-traces $80{,}532$ line-of-sight galaxies across a $7.5^{\prime}\times7.5^{\prime}$ field, leveraging an accelerated JAX-based pipeline. The framework integrates intra-cluster light, multi-band SEDs, and simplified instrumental effects to produce realistic mock images in the CSST-MCI bands ($\mathrm{CBU}$, $\mathrm{CBV}$, $\mathrm{CBI}$), enabling robust testing of data pipelines and lens-modeling algorithms. This work thus provides essential data products and methodology for studying dark matter, dark energy, and galaxy evolution with CSST-MCI observations.

Abstract

The Multi-Channel Imager (MCI), one of the instruments aboard the China Survey Space Telescope (CSST), is designed to simultaneously observe the sky in three filters, covering wavelengths from the near-ultraviolet (NUV) to the near-infrared (NIR). With its large field of view ($7.5^{\prime}\times7.5^{\prime}$), MCI is particularly well-suited for observing galaxy clusters, providing a powerful tool for investigating galaxy evolution, dark matter and dark energy through gravitational lensing. Here we present a comprehensive simulation framework of a strong lensing cluster as observed by MCI, aiming to fully exploit its capabilities in capturing lensing features. The framework simulates a strong lensing cluster from the CosmoDC2 catalog, calculating the gravitational potential and performing ray-tracing to derive the true positions, shapes and light distribution of galaxies within the cluster field. Additionally, the simulation incorporates intra-cluster light (ICL) and spectral energy distributions (SEDs), enabling further strong lensing analyses, such as ICL seperation from galaxy light and mass reconstruction combining strong and weak lensing measurements. This framework provides a critical benchmark for testing the MCI data pipeline and maximizing its potential in galaxy cluster research.

Figures (7)

• Figure 1: Redshift and CBU, CBV, CBI magnitude distributions of the 80,532 source galaxies within the $7.5^{\prime}\times7.5^{\prime}$ lightcone of the simulated MCI cluster.
• Figure 2: Left panel: Convergence map of the simulated MCI cluster. Right panel: Illustration of the light rays on the lens plane (blue dots) and their mapped positions on the source plane (orange dots) due to the deflection of gravitational lensing.
• Figure 3: Galaxy distributions within the central region ($60^{\prime\prime} \times 60^{\prime\prime}$) of the simulated cluster, accounting for the gravitational lensing effect.
• Figure 4: An illustration of the multiply lensed arc. The 'source' shows where the source is originally lying. The 'image' indicates its appearance and position after being deflected by the lens.
• Figure 5: Illustration of the ICL mock in the CBV band. The image is presented within $4000 {\times} 4000$ pixels (corresponding to $200^{\prime\prime} {\times} 200^{\prime\prime}$). Top Left: Luminosity distribution of cluster member galaxies. The second-order moment of the galaxy position distribution is represented by the black dashed ellipse in the center of the figure. Top Right: Simulated ICL image modeled using the NFW profile. Bottom Left: Mock of asymmetric ICL luminosity distribution. Bottom Right: The luminosity distribution of the sum of the asymmetric ICL and the member galaxies of the cluster.