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

TL;DR

This paper compares different methods of mapping the local universe's matter density, highlighting discrepancies and limitations of galaxy catalogs and velocity-based models, especially in obscured regions like the Zone of Avoidance.

Contribution

It provides a detailed comparison between the CosmicFlows density fields and Biteau's galaxy catalog, revealing significant regional differences and issues with galaxy catalog completeness.

Findings

Factor-of-two density differences in some regions

Large discrepancies in the Zone of Avoidance

Misalignments between structure positions in velocity and galaxy data

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 unseen galaxies. Here we compare the density field proposed by J. Biteau (2021) with the quasi-linear density field of CosmicFlows2 (Y. Hoffman et al. 2018) and the mean posterior field of CosmicFlows4 (A. Valade 2026). We find factor-of-two level differences in some regions and even larger discrepancies toward the Galactic center zone of avoidance (ZoA), defined by absolute longitude less than 30 degrees and absolute latitude less than 20 degrees, as filled by Biteau using cloning. Within 11 Mpc the density field is well determined by the Local Volume catalog (I. D. Karachentsev et al. 2018), which is directly incorporated by Biteau, and is preferred over the CosmicFlows modeling. At larger distances Biteau (2021) is also preferred for the direction and integrated mass of non-obscured structures, but the radial mass distribution is less robust due to line-of-sight peculiar velocities. Within the ZoA the galaxies of Biteau (2021) are entirely fictitious and their use is ill advised except where they do not contribute to the observable of interest. Moreover, as shown by the South Pole Wall, discovered by CosmicFlows but absent from galaxy catalogs, obscuration can be significant even outside the ZoA. Unexpectedly, we find that the angular positions of structures in CosmicFlows are sometimes misaligned with their true positions as seen in galaxy catalogs outside the ZoA.