Everything Everywhere All At Once: A Hierarchical Framework for Mapping Anisotropies in the Local Universe
Abstract
We present a Bayesian hierarchical forward model for mapping the local luminosity-density field from heterogeneous redshift surveys. By dividing the survey volume into angular cells and redshift shells, we model the observed galaxy distribution directly in apparent-magnitude and redshift space. This allows us to infer cell-level luminosity functions and densities while preserving each survey's unique selection function. Simultaneously, the ensemble of cells constrains the cosmic-mean luminosity function, its redshift evolution, and the hyperparameters describing cell-to-cell variation. We apply the framework to 2MRS, 6dFGS, and GAMA over 0.005<z<0.065, combining wide sky coverage with deeper and fainter galaxy samples. The model successfully recovers global J-band luminosity-function parameters and a mean luminosity density consistent with previous low-redshift measurements. The inferred luminosity-density scatter decreases with volume, consistent with the cosmic-variance amplitude expected in a ΛCDM universe. Within the volume we probe, we find no evidence for a large coherent underdensity. Instead, the local Universe is broadly consistent with smooth evolution and cosmic variance. The nearest shell at z ≃ 0.01 is the clearest exception, lying ≃ 0.12~dex (≃ 25%) below the smooth global model, a −2.6σ underdensity with a one-sided significance of ≃ 99.5%. This framework offers a scalable architecture for mapping cosmic density fields with next-generation wide and deep surveys.
Versions
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BibTeX
@misc{bansal2026everything,
title = {{Everything Everywhere All At Once: A Hierarchical Framework for Mapping Anisotropies in the Local Universe}},
author = {Aryan Bansal and Edward N. Taylor and Michelle Cluver and Matthew Colless},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.36462},
eprint = {2609.36462},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.36462},
}
RIS
TY - UNPB
TI - Everything Everywhere All At Once: A Hierarchical Framework for Mapping Anisotropies in the Local Universe
AU - Aryan Bansal
AU - Edward N. Taylor
AU - Michelle Cluver
AU - Matthew Colless
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.36462
UR - https://arxiv.org/abs/2609.36462
AB - We present a Bayesian hierarchical forward model for mapping the local luminosity-density field from heterogeneous redshift surveys. By dividing the survey volume into angular cells and redshift shells, we model the observed galaxy distribution directly in apparent-magnitude and redshift space. This allows us to infer cell-level luminosity functions and densities while preserving each survey's unique selection function. Simultaneously, the ensemble of cells constrains the cosmic-mean luminosity function, its redshift evolution, and the hyperparameters describing cell-to-cell variation. We apply the framework to 2MRS, 6dFGS, and GAMA over 0.005<z<0.065, combining wide sky coverage with deeper and fainter galaxy samples. The model successfully recovers global J-band luminosity-function parameters and a mean luminosity density consistent with previous low-redshift measurements. The inferred luminosity-density scatter decreases with volume, consistent with the cosmic-variance amplitude expected in a ΛCDM universe. Within the volume we probe, we find no evidence for a large coherent underdensity. Instead, the local Universe is broadly consistent with smooth evolution and cosmic variance. The nearest shell at z ≃ 0.01 is the clearest exception, lying ≃ 0.12~dex (≃ 25%) below the smooth global model, a −2.6σ underdensity with a one-sided significance of ≃ 99.5%. This framework offers a scalable architecture for mapping cosmic density fields with next-generation wide and deep surveys.
ER -