Separate Universe Void Bias

TL;DR

This paper measures the linear bias of cosmic voids using separate universe simulations, validating the results through clustering comparisons and analyzing the contributions to bias from halo bias and dynamical effects.

Contribution

First measurement of void bias in separate universe simulations, with detailed analysis of bias contributions and validation against clustering bias.

Findings

Excellent agreement between response bias and clustering bias methods.

Identification of two main contributions to void bias: halo bias and dynamical effects.

Void profiles are sensitive to background density, informing cosmological models.

Abstract

Voids have emerged as a novel probe of cosmology and large-scale structure. These regions of extreme underdensity are sensitive to physics beyond the standard model of cosmology, and can potentially be used as a testing ground to constrain new physics. We present the first determination of the linear void bias measured in separate universe simulations. Our methods are validated by comparing the separate universe response bias with the clustering bias of voids. We find excellent agreement between the two methods for voids identified in the halo field and the down-sampled dark matter field. For voids traced by halos, we identify two different contributions to the bias. The first is due to the bias of the underlying halo field used to identify voids, while the second we attribute to the dynamical impact of long-wavelength density perturbations on void formation and expansion. By measuring these contributions individually, we demonstrate that their sum is consistent with the total void bias. We also measure the void profiles in our simulations, and determine their separate universe response. These can be interpreted as the sensitivity of the profiles to the background density of the Universe.