Towards precision cosmology with Voids x CMB correlations (I): Roman-Agora mock catalogs and pipeline validation

TL;DR

This work tackles the challenge of generating realistic Roman-like mock catalogs suited for CMB–LSS cross-correlations by introducing analog matching, a nearest-neighbor mapping of Roman reference galaxies to halos in the Agora simulation. By constructing 16 mock realizations with varying levels of fidelity (including halo mass, environment, and ELG-type information) and validating them against a dust-filtered Roman reference catalog through one- and two-point statistics and void measurements, the authors demonstrate that halo mass–based analog matching reliably reproduces both clustering and void statistics for ELG tracers, while including environmental information can reduce robustness when the underlying dark matter field is not shared. Crucially, void statistics emerge as a sensitive, independent diagnostic that can reveal mismatches not evident in power spectra alone. The resulting Roman-Agora mocks provide a flexible, general framework for LSS–CMB studies and set the stage for assessing how mock construction choices impact cosmological inferences, including future Void×CMB lensing analyses across multiple surveys.

Abstract

We construct and validate a set of multi-purpose mock galaxy catalogs designed to capture, to different degrees of accuracy, the main characteristics of the Nancy Grace Roman Space Telescope survey. These catalogs provide a foundation for void statistics and various CMB cross-correlation analyses. Our approach differs from traditional halo occupation or abundance matching methods by directly translating a reference mock catalog -- containing basic properties of the host halos -- into a new simulation (in our case Agora). This technique, which we call analog matching, assigns a halo counterpart in the new simulation to each reference galaxy through a nearest-neighbor search in a multi-dimensional parameter space. This space can include halo mass, environmental measures and other galaxy-specific attributes. By varying the composition of this parameter vector, we can generate catalogs of differing complexity and conduct systematic tests to examine the influence of modelling choices on LSS statistics. We find that analog matching based on halo mass alone, or halo mass and galaxy-type indicators, successfully reproduces the expected Roman emission-line galaxy statistics. We also show that reproducing two-dimensional galaxy clustering does not guarantee consistent void properties. Our results highlight the importance of matching void statistics for improved mock accuracy, and demonstrate that measuring voids provides independent and sensitive constraints on galaxy-halo connections beyond the matter power spectrum. An important by-product of our setup is that it is fully general and can be applied to any combination of simulation and reference catalog, provided that the desired parameter space for both is specified. The resulting Roman-Agora mock catalogs offer a versatile resource for LSS x CMB studies and a benchmark for assessing the impact of mock accuracy on cosmological observables.

Figures (8)

• Figure 1: Flowchart illustrating the datasets and methodology employed in this paper.
• Figure 2: Slice at $z = 1.012$ with thickness $\Delta z = 0.01$, illustrating 3D and 2D voids identified with the void finder with smoothing scales of 5 and 10 Mpc $h^{-1}$. To maintain clarity, only voids centered at this exact redshift are plotted; otherwise, including the full slice width would result in 3D voids covering the map. Specifically, we identify 525 3D voids (restricted to this redshift), compared to 470 2D voids at $\rm sm_{VF} = 5$ Mpc $h^{-1}$ and 209 at $\rm sm_{VF} = 10$ Mpc $h^{-1}$. Their average sizes are $24.91, 50.38,$ and $83.90$ Mpc $h^{-1}$ (corresponding to angular sizes of $0.42, 0.84$, and $1.48$ degrees), respectively.
• Figure 3: One-point statistic distributions for the generated void catalogs. The rows correspond to the void redshift (top), void size (middle), and minimum density (bottom) distributions for the respective void samples. Each column represents a different mock catalog type. Different colors denote a different tracer bias. The bottom sub-panels display the residuals, defined as the relative difference with respect to the Roman reference catalog. Error bars are Poissonian.
• Figure 4: Two-point statistics including the galaxy power spectrum (top panel) and the galaxy-void cross-correlation function. For the latter, the monopole of both 2D and 3D voids and the quadrupole of the 3D voids are included. Each column corresponds to a different mock catalog type, and each color represents a different tracer bias. The residuals in the bottom sub-panels show the relative difference compared to the Roman reference catalog. Error bars are derived from jackknife estimates.
• Figure 5: Sensitivity of 3D and 2D void finders to under- and over-sampling the tracer galaxy field.