Everything everywhere all at once: a hierarchical framework for mapping anisotropies in the local Universe
Year: 2026
Type: article
Abstract: 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 $0.005\lt z\lt 0.065$, 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 $z \simeq 0.01$ is the clearest exception, lying ${\simeq} 0.12$ dex (${\simeq} 25 {{\ \rm per\ cent}}$) below the smooth global model, a $-2.6\sigma$ underdensity with a one-sided significance of ${\simeq} 99.5 {{\ \rm per\ cent}}$. This framework offers a scalable architecture for mapping cosmic density fields with next-generation wide and deep surveys.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
OpenAlex ID: W7214903306