A semi-analytical mock galaxy catalog for the CSST extragalactic surveys from the Jiutian simulations

TL;DR

The work tackles the challenge of producing realistic, forward-modeled mock catalogs for the CSST extragalactic surveys by building an end-to-end pipeline that starts from Jiutian N-body simulations and yields light-cone galaxy catalogs through the GAEA semi-analytic model, HBTHBT+ merger trees, StarDuster SEDs, and the Blic interpolation-based light-cone builder. It validates the mocks against a broad set of observables (stellar mass functions, luminosity functions, gas fractions, size-mass relations, and clustering) and provides CSST photometric and redshift forecasts, demonstrating the utility of the mocks for survey planning. The study also compares interpolation schemes for light-cone construction, identifying cubic interpolation as the most accurate and stable default. Data products including subhalo catalogs and multi-band light-cones up to redshift $z=5$ are prepared for public release to support CSST science while acknowledging caveats such as high-redshift star-formation rate discrepancies and satellite-galaxy color distributions that warrant future improvements.

Abstract

We introduce a mock galaxy catalog built for the CSST extragalactic surveys using the primary runs of the Jiutian $N$-body simulation suites. The catalogs are built by coupling the GAlaxy Evolution and Assembly (GAEA) semi-analytical model of galaxy formation with merger trees extracted from the simulations using the Hierarchical Bound-Tracing (HBT+) algorithm. The spectral energy distributions (SEDs) and broadband magnitudes are computed using the neural-network-based stellar population synthesizer StarDuster, which is trained on radiative transfer simulations to account for detailed galaxy geometry in modeling dust obscuration. Galaxy light-cones up to $z=5$ are subsequently generated with the BLiC light-cone builder which interpolates the properties of galaxies over time using an optimized interpolation scheme. The resulting catalogs exhibit good convergence in many statistical properties of the galaxy population produced from two different resolution simulations. The catalogs reproduce a number of observed galaxy properties across a range of galaxy mass and redshift, including the stellar mass functions, the luminosity function, gas mass fraction, galaxy size-mass relation and galaxy clustering. We also present the photometric and redshift distributions of galaxies expected to be observed in the CSST surveys.

Figures (15)

• Figure 1: Transmission curves of various photometric filters adopted in this work, as labeled.
• Figure 2: Accuracy in interpolating the galaxy position. Different interpolation schemes (shown with different colors as labeled) are adopted to interpolate the trajectory of each galaxy in the Illustris-3 simulation, using snapshots both before and after the 68th snapshot, with a time separation of $0.3$ Gyr between them. The interpolation results at the time of the 68th snapshot is compared against the snapshot itself, and the distribution of the residuals in the predicted coordinates are shown for each of the $(x,y,z)$ dimension. The bottom right panel shows the total displacement, $\Delta r=\sqrt{\Delta x^2+\Delta y^2 +\Delta z^2}$. Solid lines show the distribution of all galaxies, while the dashed lines show the results for satellite galaxies only.
• Figure 3: Subhalo peak mass versus stellar mass for Jiutian-1G galaxies. The red dash-dotted curve shows the 96% lower bound of the peak mass at a fixed stellar mass. At a stellar mass of $M_{\rm \star, softlim}=10^{8.74} \rm M_\odot$, this peak limit reaches 100 particles as marked by the blue dashed horizontal line. The yellow dash-dotted curve shows the 96% upper limit of the stellar mass at a fixed peak mass. For a peak mass of 20 particles, this stellar mass limit reaches $M_{\rm \star, hardlim}=10^{7.50} \rm M_\odot$. The vertical blue band marks the mass range between the soft and hard stellar mass limits.
• Figure 4: Stellar mass functions for Jiutian-1G (blue) and 2G (red) at multiple redshifts, compared with observational data Ilbert2013AAXu2022WangYR2024. For each simulation mass function, a vertical band of the corresponding color marks the range spanned between the hard and soft completeness limits as determined following Figure \ref{['fig:mp_ms1G']} at the corresponding redshift.
• Figure 5: $z=0$ luminosity functions in SDSS bands of gaea galaxies in Jiutian-1G. Blue curves show the distribution of intrinsic magnitudes, while gray curves include dust attenuation. In each panel, the vertical band span the hard and soft completeness limits in the modelled magnitudes. Observational measurements from the GAMA survey by Driver2012MNRAS and Loveday2012MNRAS are also shown by symbols as labelled.