Roman-agora Catalogs Enable Precision Cosmology Via Voids X CMB Correlations

Understanding the universe’s expansion and the nature of dark energy requires increasingly precise cosmological measurements, and a promising new avenue involves studying the vast, empty regions of space known as cosmic voids in conjunction with observations of the cosmic microwave background. Mar Pérez Sar, Carlos Hernández Monteagudo, and András Kovács, from the Instituto de Astrofísica de Canarias and the Lendület “Momentum” Large-Scale Structure Research Group, along with Alice Pisani from CPPM, Aix-Marseille Université, have developed a new method for creating realistic simulations of future galaxy surveys, specifically designed to test this approach. The team constructed detailed mock galaxy catalogs mirroring the expected data from the upcoming Nancy Grace Roman Space Telescope, employing a technique called analog matching to accurately represent the distribution of galaxies within these voids. This work demonstrates that accurately simulating voids is crucial for reliable cosmological analysis, offering an independent way to refine our understanding of the connection between galaxies and the underlying dark matter distribution, and ultimately, to constrain the universe’s fundamental properties.

These catalogs will serve as a foundation for studying voids, which are large underdense regions in the distribution of galaxies, and for exploring correlations with the Cosmic Microwave Background (CMB). A key achievement of this work involved identifying and correcting a significant issue with the peculiar velocities in the Agora simulation, which were initially inverted. The team discovered this error through multiple tests, including analyzing void statistics, examining angular redshift fluctuations, and comparing results with an independent simulation called Skyline.

Correcting the velocities involved simply flipping their sign, restoring physical consistency to the simulation. Investigations also revealed that the smoothing scale used in the void finder significantly impacts the resulting void statistics, and while differences in stellar mass and star formation rate calibration exist between the Agora and Roman catalogs, these offsets do not drastically affect the ability to recover expected clustering biases. Detailed analysis in the appendices demonstrates the careful calibration and validation processes undertaken. One appendix compares the distributions of halo mass, stellar mass, star formation rate, and specific star formation rate between the Agora simulation and the Roman reference catalog, finding slight systematic shifts that do not significantly impact analog matching. Another appendix presents void statistics for a 2D void finder using a smaller smoothing scale, showing more pronounced differences between the mock catalogs compared to a larger scale. They introduced an innovative technique called analog matching, which translates properties from an existing mock catalog into the Agora simulation by identifying nearest neighbors in a multi-dimensional parameter space. This approach allows the generation of catalogs with varying complexity, systematically testing the influence of different modeling choices on measurements of large-scale structure. Analyzing voids provides independent and sensitive constraints on the connections between galaxies and the halos of dark matter surrounding them, extending beyond traditional matter power spectrum analysis. The resulting Roman-Agora mock catalogs offer a versatile tool for cross-correlation studies between large-scale structure and the CMB, providing a benchmark for assessing the impact of mock catalog accuracy on cosmological observables. This method constructs new simulations by directly linking galaxies in a reference catalog to corresponding halos within a different simulation, using a nearest-neighbor search based on properties like halo mass and environment. By adjusting the parameters used in this matching process, researchers can systematically test how different levels of detail affect the accuracy of the resulting mock catalogs. These mock catalogs offer a valuable tool for studying the relationship between large-scale structures in the universe and the cosmic microwave background, and provide a benchmark for assessing the impact of catalog construction on cosmological measurements. While acknowledging some discrepancies at very large scales in their simulations, the authors consider these unlikely to significantly affect studies of cosmic voids, which focus on smaller scales. The analog matching framework itself is broadly applicable, capable of linking any reference catalog to any simulation given appropriate parameter specifications.