# How does the grouping scheme affect the Wiener Filter reconstruction of the local Universe?

## TL;DR

This study examines how different grouping schemes and Hubble constant values influence Wiener Filter reconstructions of the local Universe's velocity and density fields, emphasizing the importance of balancing grouping and constraints.

## Contribution

It systematically analyzes the effects of grouping schemes and H0 values on Wiener Filter reconstructions, highlighting the impact on structure contrast and infall patterns.

## Key findings

- Larger H0 increases infall onto local structures.
- Bias minimization suppresses H0-related infall effects.
- Less aggressive grouping enhances structure contrast.

## Abstract

High quality reconstructions of the three dimensional velocity and density fields of the local Universe are essential to study the local Large Scale Structure. In this paper, the Wiener Filter reconstruction technique is applied to galaxy radial peculiar velocity catalogs to understand how the Hubble constant (H0) value and the grouping scheme affect the reconstructions. While H0 is used to derive radial peculiar velocities from galaxy distance measurements and total velocities, the grouping scheme serves the purpose of removing non linear motions. Two different grouping schemes (based on the literature and a systematic algorithm) as well as five H0 values ranging from 72 to 76 km/s/Mpc are selected. The Wiener Filter is applied to the resulting catalogs. Whatever grouping scheme is used, the larger H0 is, the larger the infall onto the local Volume is. However, this conclusion has to be strongly mitigated: a bias minimization scheme applied to the catalogs after grouping suppresses this effect. At fixed H0, reconstructions obtained with catalogs grouped with the different schemes exhibit structures at the proper location in both cases but the latter are more contrasted in the less aggressive scheme case: having more constraints permits an infall from both sides onto the structures to reinforce their overdensity. Such findings highlight the importance of a balance between grouping to suppress non linear motions and preserving constraints to produce an infall onto structures expected to be large overdensities. Such an observation is promising to perform constrained simulations of the local Universe including its massive clusters.