How well is the local Large Scale Structure of the Universe known? CosmicFlows vs. Biteau's Galaxy Catalog with Cloning

TL;DR

The paper assesses how well the local Large Scale Structure density is known by comparing the CosmicFlows4/2 density fields, derived from peculiar velocities, with Biteau's galaxy-catalog-based density (B21) that uses cloning to fill the Zone of Avoidance. It introduces a shell-based smoothing and Healpix-based mapping to enable direct comparison, highlighting substantial region-by-region differences, especially due to cloning in ZoA and to distance-assignment methods. The authors find that Biteau’s cloning inflates central-shell densities and that the LV region ($d<11$ Mpc) is best described by Biteau, while CF4 provides a more reliable, self-consistent density field beyond the ZoA; combining the strengths of both approaches could improve local mass maps. These results have implications for predicting UHECR anisotropies and diffuse signals, and they suggest developing ZoA-filling methods that reweight observed galaxies with dust and spectral information to reduce artefacts.

Abstract

Knowledge of the actual density distribution of matter in the local universe is needed for a variety of purposes -- for instance, as a baseline model for ultrahigh energy cosmic ray sources in the continuum limit and for predicting the diffuse Dark Matter annihilation signal. Determining the local mass density and velocity distribution is the aim of the CosmicFlows project. An alternate approach is based on catalogs of galaxies, supplemented with some scheme for filling in for unseen galaxies. Here, we compare the density field proposed by Biteau (2021) with the quasi-linear density field of CosmicFlows2 (Hoffman et al. 2018) and the mean posterior field of CosmicFlows4 (Valade 2026). We find factor-two level differences in some regions and even greater in regions toward the Galactic center zone of avoidance (ZoA) (|l| < 30°, |b| < 20°) as filled by Biteau using "cloning". Within 11 Mpc the density field is well-determined by the Local Volume catalog (Karachentsev et al. 2018) which Biteau directly incorporates; at larger distances, Biteau (2021) should not be used in the ZoA where "galaxies" are entirely fictitious but otherwise is to be preferred over CosmicFlows emphasizing the direction and integrated mass of structures; the radial distribution of mass in Biteau (2021) is less robust due to line-of-sight peculiar velocities. The angular positions of structures in CosmicFlows are sometimes not congruent with evidence in the galaxy catalog.

Figures (7)

• Figure 1: Mean mass over-density in spherical shells at distance $d$ derived from CosmicFlows2, CosmicFlows4 and the Biteau Catalog, with the main plots extending from 0-100 Mpc and the inset covering the range 1000-350 Mpc. The thin lines show the same, but excluding the Zone of Avoidance (not inluding CF2, for legibility).
• Figure 2: Skymaps of logarithmic mass density excursion derived from CosmicFlows2, CosmicFlows4, and Biteau's catalog smoothed by 5 and 10 Mpc and averaged over the indicated radial shell, except that the rightmost entry in the first row (0-20 Mpc) uses "angular smoothing" to better reveal the actual data. In all plots the supergalactic plane is indicated in yellow and the cloning region is outlined in green -- inside, Biteau's density model simply mirrors the density in the observed region immediately above or below the green line, as described in the text and seen by eye. The major clusters are labeled at their corresponding positions. The boxes in black in the third panel in the top row indicate the angular regions discussed in Fig. \ref{['fig:selectLoSden']}.
• Figure 3: Total mass of galaxies within 10 Mpc of galaxies whose mass is (0.5-2)$M_{\rm MW}$, relative to the mass within 10 Mpc of the Milky Way, according to the Biteau catalog.
• Figure 4: 3D visualization of galaxies in the Local Volume. Points are shown in Galactic Cartesian coordinates, with the $x$-axis pointing toward the Galactic Center. The cyan plane indicates the Galactic plane, and the yellow plane shows the Supergalactic plane. Colors denote the main galaxy groups: Milky Way (black) and M31 (green), M81 and NGC 2403 (orange), Centaurus A and M83 (red), and IC 342 (purple). Point opacity encodes stellar mass, scaled linearly with logarithmic mass. The interactive version of this figure is available online at https://yl10327.github.io/LV-3D/LV_plotly.html. The interactive version of the figure without planes is available online at https://yl10327.github.io/LV-3D/LV_plotly_noplane.html.
• Figure 5: Upper four panels: Overdensity as a function of radius in 4 illustrative angular regions containing clusters. Lower left: Overdensity as a function of radius in a major void direction, showing that although the CF4 density field is smoother it accurately matches the 5 Mpc Biteau density field in the void distance range, beyond the local volume. The last plot shows the mass density in the North and South zone of avoidance regions as modeled in CF4 (brown and gold lines) compared to Biteau's cloning scheme (green and blue lines). One sees that the cloning significantly distorts the mass density in the ZoA, commonly disagreeing with CF4 by a factor 2-5.