Weak gravitational lensing of intrinsically aligned galaxies

TL;DR

This paper models how weak gravitational lensing affects the ellipticity correlations of intrinsically aligned galaxies, revealing measurable impacts on ellipticity spectra and mode conversions, especially relevant for future large-scale surveys.

Contribution

It introduces a novel model combining intrinsic galaxy alignments with weak lensing effects, including E/B-mode spectra and multipole correlations, using a tidal torquing framework and CMB polarization methodology.

Findings

Lensing deflection alters ellipticity spectra by ~5% (E-modes) and ~30% (B-modes) for EUCLID.

Lensing causes E/B-mode conversion and multipole correlations, breaking homogeneity.

Small-scale ellipticity spectra are significantly shaped by lensing effects, observable in future surveys.

Abstract

Subject of this paper is the weak lensing effect on galaxies that show intrinsically correlated ellipticities. In our model, we investigate the distortion of the ellipticity field if the galaxies experience an apparent shift in their position by weak lensing deflection and compare this effect to the shearing effect induced by tidal fields. Starting with a derivation of intrinsic ellipticity spectra by employing a tidal torquing model generating galactic angular momenta, we model the galaxy ellipticity by assuming that the galactic disk forms perpendicularly to the host halo angular momentum direction and derive intrinsic ellipticity E-mode and B-mode spectra from the angular momentum statistics. The lensing effect on the ellipticity field is modeled by employing the methodology developed in the framework of lensing of the cosmic microwave background polarisation. For EUCLID, ellipticity correlations are altered by lensing deflection on multipoles l>1000 by ~5% for the ellipticity E-modes and by ~30% for the B-modes, while a shallower survey would exhibit larger changes on larger angular scales. In addition to the convolving effect of lensing on the ellipticity spectra we investigate the E/B-mode conversion, and discuss the possibility of measuring correlations between different multipoles which is evoked by the homogeneity breaking effect of the lensing displacement. Our conclusion is that although shape correlations generated by weak gravitational shear is dominant, the shifting effect due to lensing is shaping the ellipticity spectra on small angular scales and causes a number of interesting phenomena, which might be observable by future surveys.