Everything everywhere all at once: a hierarchical framework for mapping anisotropies in the local Universe
- 1Centre for Astrophysics and Supercomputing, Swinburne University of Technology , Hawthorn, VIC 3122 ,
- 2Research School of Astronomy and Astrophysics, Australian National University , Canberra, ACT 2611 ,
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 the Two Micron All-Sky Redshift Survey, 6dF Galaxy Survey, and Galaxy And Mass Assembly survey over 0.005lt zlt 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 Lambda cold dark matter 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 per cent) below the smooth global model, a −2.6σ underdensity with a one-sided significance of ≃ 99.5 per cent. This framework offers a scalable architecture for mapping cosmic density fields with next-generation wide and deep surveys.
Versions
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BibTeX
@article{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},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1867},
url = {https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1867/8865304},
note = {CC BY 4.0},
}
RIS
TY - JOUR
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 - 2026/10/05
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1867
UR - https://academic.oup.com/mnras/article/doi/10.1093/mnras/stag1867/8865304
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 the Two Micron All-Sky Redshift Survey, 6dF Galaxy Survey, and Galaxy And Mass Assembly survey over 0.005lt zlt 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 Lambda cold dark matter 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 per cent) below the smooth global model, a −2.6σ underdensity with a one-sided significance of ≃ 99.5 per cent. This framework offers a scalable architecture for mapping cosmic density fields with next-generation wide and deep surveys.
SN - 0035-8711
SN - 1365-2966
ER -