B-modes from galaxy cluster alignments in future surveys

TL;DR

This paper forecasts the detectability of B-mode signals from galaxy cluster intrinsic alignments in future and current surveys, using a validated theoretical model, highlighting the potential for direct IA studies.

Contribution

It introduces a perturbative EFT-based model for IA multipoles to forecast B-mode detectability in upcoming surveys, validated against simulations.

Findings

Forecasted SNR of ~12 for LSST, indicating strong detectability.

SNR of ~5 for SDSS redMaPPer clusters, suggesting possible detection.

SNR of ~3 for DESY1 clusters, within reach with accurate redshift data.

Abstract

Intrinsic alignment (IA) of source galaxies represents an important contaminant for upcoming cosmic shear surveys. In particular, it is expected on general grounds that IA contains a B-mode while the weak lensing signal does not. Thus, a detection of B-modes offers the possibility to study directly the IA signal of the sources. Galaxy clusters exhibit strong IA and are therefore a natural candidate to look for a B-mode signal. We forecast the signal-to-noise ratio (SNR) for B-modes from IA of galaxy clusters in the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). We use a perturbative model for the IA multipoles based on the Effective Field Theory of Intrinsic Alignments (EFT of IA), which has recently been validated against N-body simulations. We forecast SNR $\approx 12$ and find that this detectability is not significantly impacted by different analysis choices. Lastly, we also apply our forecast to clusters in the redMaPPer SDSS and DESY1 samples. We find SNR $\approx 5$ and SNR $\approx 3$, respectively, suggesting a detection is within reach, provided accurate redshift information is available.