Measurement of Void Bias Using Separate Universe Simulations

TL;DR

This paper uses separate universe simulations to accurately measure void bias parameters, confirming the peak-background split's effectiveness and detecting quadratic void bias for the first time.

Contribution

It introduces the application of SUS to measure void bias, including the first detection of quadratic bias in simulations and comparison between halo and dark matter voids.

Findings

Void bias depends on void radius relative to the distribution peak.

Linear bias agrees with large-scale cross power spectrum measurements.

Quadratic bias is negative for small |b_1| and positive for larger |b_1|.

Abstract

Cosmic voids are biased tracers of the large-scale structure of the universe. Separate universe simulations (SUS) enable accurate measurements of this biasing relation by implementing the peak-background split (PBS). In this work, we apply the SUS technique to measure the void bias parameters. We confirm that the PBS argument works well for underdense tracers. The response of the void size distribution depends on the void radius. For voids larger (smaller) than the size at the peak of the distribution, the void abundance responds negatively (positively) to a long wavelength mode. The linear bias from the SUS is in good agreement with the cross power spectrum measurement on large scales. Using the SUS, we have detected the quadratic void bias for the first time in simulations. We find that $ b_2 $ is negative when the magnitude of $ b_1 $ is small, and that it becomes positive and increases rapidly when $ |b_1| $ increases. We compare the results from voids identified in the halo density field with those from the dark matter distribution, and find that the results are qualitatively similar, but the biases generally shift to the larger voids sizes.