Evolution of intrinsic ellipticity correlations due to peculiar motion

TL;DR

This paper models how galaxy ellipticity correlations evolve over time due to peculiar motion, showing that such motions cause measurable distortions in the ellipticity field, especially at larger scales and lower redshifts.

Contribution

It introduces a novel approach to quantify the impact of peculiar motion on intrinsic ellipticity correlations using Lagrangian perturbation theory and analogies with CMB lensing.

Findings

Peculiar motion reduces ellipticity correlations by up to 10% at high multipoles for EUCLID.

B-mode spectra are suppressed by up to 60% at l~3000 due to peculiar motion.

E/B-mode conversion effects are small but present, similar to CMB lensing phenomena.

Abstract

Topic of this paper is the time-evolution of intrinsic correlations of galaxy ellipticities due to peculiar motion. In our model, the galaxy ellipticities are determined from the angular momentum of their host haloes, which can be computed from the fluctuations statistics of a Gaussian random field. Subsequent peculiar motion distorts the ellipticity field and causes changes in the ellipticity correlations. Using analogies between this problem of shifted ellipticity tensors and the displacements of polarisation tensors in gravitational lensing of the cosmic microwave background we compute E-mode and B-mode spectra of the time-evolved ellipticity field, where the displacements are modelled with first and second order Lagrangian perturbation theory. For EUCLID, ellipticity correlations are decreased on large multipoles l >1000, amounting to up to 10% in the E-mode spectrum C_E^epsilon(l) and up to 60% in the B-mode spectrum C_B^epsilon(l) at l~3000 due to the dispersing effect of peculiar motion. E/B-mode conversion in analogy to CMB-lensing is present but small. We conclude that distortions of the ellipticity field due to peculiar motion is not affecting the prediction of ellipticity models on the scales relevant for lensing in the case of EUCLID's galaxy distribution, but should affect larger scales for surveys at lower redshifts.