Approximations for the divergence of the local large-scale structure velocity field and its implications for Tilted Cosmology

TL;DR

This paper analyzes the divergence of the local large-scale structure velocity field using reconstructed data, exploring its implications for tilted cosmology and highlighting the need for improved velocity reconstructions.

Contribution

It introduces a method to characterize the divergence of the local velocity field from survey data and discusses its implications for tilted cosmology models.

Findings

Reconstructed velocity divergence has potential biases affecting cosmological interpretations.

Apparent deceleration parameter values are computed and compared with tilted-universe predictions.

Results suggest the necessity for more accurate velocity field reconstructions to constrain cosmological models.

Abstract

We characterize the peculiar velocity field of the local large-scale structure reconstructed from the $2M++$ survey, by treating it as a fluid, extracting the divergence via different approximations over a range pf averaged scales. This reconstructed field is important for cosmology, since it was used to correct the peculiar redshifts of the last SNIA compilation Pantheon+. The results have intriguing implications for the LLSS fluid dynamics and particularly for the ``Tilted Cosmology'' model, although those results have to be taken carefully as the velocity field could contain significant bias due to the reconstruction procedure. Those possible bias and its influence in our results are discussed. Representative values of the apparent deceleration parameter ($\Tilde{q}$) are computed, in order to compare our results with the theoretical predictions of the tilted-universe scenario. We conclude that better velocity field reconstructions are necessary in order to constrain the parameters implied in LLSS research and alternative cosmologies.