An alternative approach to modelling a cosmic void and its effect on the cosmic microwave background

TL;DR

This paper introduces a tetrad-based method for modeling cosmic voids and compares it with the standard LTB approach, showing that velocity profiles are crucial for constraining void properties using observational data.

Contribution

The paper presents a novel tetrad-based framework for modeling cosmic voids and demonstrates its differences from the LTB formalism in fitting observational data.

Findings

Void models can differ significantly between approaches while fitting observations.

Velocity profiles are essential for constraining void characteristics.

Existing data do not tightly constrain present-day density and velocity profiles.

Abstract

We apply our tetrad-based approach for constructing spherically-symmetric solutions in general relativity to modelling a void, and compare it with the standard Lema\^itre-Tolman-Bondi (LTB) formalism. In particular, we construct models for the void observed in the direction of Draco in the WISE-2MASS galaxy survey, and a corresponding cosmic microwave background (CMB) temperature decrement in the Planck data in the same direction. We find that the present-day density and velocity profiles of the void are not well constrained by the existing data, so that void models produced from the two approaches can differ substantially while remaining broadly consistent with the observations. We highlight the importance of considering the velocity as well as the density profile in constraining voids.