A direct probe of cosmological power spectra of the peculiar velocity field and the gravitational lensing magnification from photometric redshift surveys

TL;DR

This paper introduces a novel method to estimate the angular power spectrum of the cosmological peculiar velocity field and gravitational lensing magnification from galaxy redshift and magnitude data, enabling high-precision constraints on large-scale structure.

Contribution

It presents a new approach leveraging galaxy redshift-magnitude relations to simultaneously probe peculiar velocities and gravitational lensing effects in photometric surveys.

Findings

High-precision measurement of velocity power spectrum at large scales.

Detection of gravitational lensing magnification effects in the power spectrum.

Potential to constrain cosmological parameters with <5% accuracy.

Abstract

The cosmological peculiar velocity field (deviations from the pure Hubble flow) of matter carries significant information on dark energy, dark matter and the underlying theory of gravity on large scales. Peculiar motions of galaxies introduce systematic deviations between the observed galaxy redshifts z and the corresponding cosmological redshifts z_cos. A novel method for estimating the angular power spectrum of the peculiar velocity field based on observations of galaxy redshifts and apparent magnitudes m (or equivalently fluxes) is presented. This method exploits the fact that a mean relation between z_cos and m of galaxies can be derived from all galaxies in a redshift-magnitude survey. Given a galaxy magnitude, it is shown that the z_cos(m) relation yields its cosmological redshift with a 1-sigma error of sigma_z~0.3 for a survey like Euclid (~10^9 galaxies at z<~2), and can be used to constrain the angular power spectrum of z-z_cos(m) with a high signal-to-noise ratio. At large angular separations corresponding to l<~15, we obtain significant constraints on the power spectrum of the peculiar velocity field. At 15<~l<~60, magnitude shifts in the z_cos(m) relation caused by gravitational lensing magnification dominate, allowing us to probe the line-of-sight integral of the gravitational potential. Effects related to the environmental dependence in the luminosity function can easily be computed and their contamination removed from the estimated power spectra. The amplitude of the combined velocity and lensing power spectra at z~1 can be measured with <~5% accuracy.