The Effect of Assembly Bias on Redshift Space Distortions

TL;DR

This study investigates how assembly bias influences redshift space distortion measurements and finds that it does not cause significant systematic errors in estimating the growth rate of cosmic structures.

Contribution

The paper demonstrates that assembly bias affects galaxy velocities but does not bias the measurement of the logarithmic growth factor in redshift space distortions.

Findings

Assembly bias correlates with stronger infall motions in high-clustering samples.

Changes in the $eta$ parameter track bias variations, not systematic errors.

No detectable systematics in growth factor estimation due to assembly bias.

Abstract

We study potential systematic effects of assembly bias on cosmological parameter constraints from redshift space distortion measurements. We use a semi-analytic galaxy formation model applied to the Millennium N-body WMAP-7 simulation to study the effects of halo assembly bias on the redshift space distortions of the galaxy correlation function. We look at the pairwise velocities of galaxies living in haloes with concentrations and ages in the upper and lower quintiles, and find that the velocity differences between these are consistent with those reported for real-space clustering analyses, i.e. samples with higher clustering also exhibit stronger infall pairwise motions. This can also be seen in the monopole and quadrupole of the redshift-space correlation function. We find that regardless of the method of measurement, the changes in the $\beta$ parameter due to different secondary halo parameters fully tracks the change in the bias Parameter. Hence, assembly bias does not introduce detectable systematics in the inferred logarithmic growth factor.