Selecting samples of galaxies with fewer Fingers-of-God

TL;DR

This paper proposes data-driven methods to select galaxy samples with fewer Fingers-of-God distortions, improving large-scale structure analysis by reducing non-perturbative effects in redshift-space maps.

Contribution

It introduces new selection techniques based on the power spectrum quadrupole and halo mass to mitigate Fingers-of-God effects in galaxy surveys.

Findings

Quadrupole sign change correlates with satellite fraction and velocity dispersion.

Excluding massive haloes reduces problematic galaxy populations.

Mitigation yields marginal improvements in perturbative modeling fits.

Abstract

The radial positions of galaxies inferred from their measured redshift appear distorted due to their peculiar velocities. We argue that the contribution from stochastic velocities -- which gives rise to Fingers-of-God (FoG) anisotropy in the inferred maps -- does not lend itself to perturbative modelling already on scales targeted by current experiments. To get around this limitation, we propose to remove FoG using data-driven indicators of their abundance that are local in nature and thus avoid selection biases. In particular, we show that the scale where the measured power spectrum quadrupole changes sign is tightly anti-correlated with both the satellite fraction and the velocity dispersion, and can thus be used to select galaxy samples with fewer FoG. In addition, we show that excluding galaxies in haloes more massive than a given mass threshold can help to discard many of the most problematic galaxies. Such selection could be achieved in practice using maps of the thermal Sunyaev-Zeldovich distortion of the cosmic microwave background frequency spectrum. These techniques could potentially improve reconstructions of the large-scale velocity and displacement fields from the redshift-space positions of galaxies. They may also extend the reach of perturbative models for galaxy clustering, though in practice we find only marginal gains when fitting one-loop EFTofLSS models to simulations with mitigated FoG due to the relevance of other effects entering at two-loop order.