Information content in mean pairwise velocity and mean relative velocity between pairs in a triplet

Abstract

Velocity fields provide a complementary avenue to constrain cosmological information, either through the peculiar velocity surveys or the kinetic Sunyaev Zel’dovich effect. One of the commonly used statistics is the mean radial pairwise velocity. Here, we consider the three-point mean relative velocity (i.e. the mean relative velocities between pairs in a triplet). Using halo catalogs from the Quijote suite of N-body simulations, we first showcase how the analytical prediction for the mean relative velocities between pairs in a triplet achieve better than 4−5% accuracy using standard perturbation theory at leading order for triangular configurations with a minimum separation of r ≥ 50 h−1 Mpc. Furthermore, we present the mean relative velocity between pairs in a triplet as a novel probe of neutrino mass estimation. We explored the full cosmological information content of the halo mean pairwise velocities and the mean relative velocities between halo pairs in a triplet. We did this through the Fisher-matrix formalism using 22 000 simulations from the Quijote suite and by considering all triangular configurations with a minimum and a maximum separation of 20 h−1 Mpc and 120 h−1 Mpc, respectively. We find that the mean relative velocities in a triplet allows a 1σ neutrino mass (Mν) constraint of 0.065 eV, which is roughly 13 times better than the mean pairwise velocity constraint (0.877 eV). This information gain is not limited to neutrino mass, but it extends to other cosmological parameters: Ωm, Ωb, h, ns, and σ8, achieving an information gain of 8.9, 11.8, 15.5, 20.9, and 10.9 times, respectively. These results illustrate the possibility of exploiting the mean three-point relative velocities to constrain the cosmological parameters accurately from future cosmic microwave background experiments and peculiar velocity surveys.

Cosmology with the kinetic Sunyaev-Zeldovich effect: Independent of the optical depth and $σ_8$

“…The bias term for the mean relative velocity between pair '23' in a triplet is similar to R h 12 , and is thus not shown in the figure. As reported in Kuruvilla & Aghanim (2021), for these triangular configurations (assuming a scale independent bias) it yields a bias factor around 1.85 for R 12 and R 23 . For the purpose of computing these ratios in the figure, we used the mean relative velocity information for matter from 30 realisations of the dark-matter only simulations, and for halo we utilised the 15,000 catalogues.…”

“…where R h i j ( 123 ) respresents the three-point mean relative velocity statistics for haloes (biased tracers), and to first approximation it can be written down as linear bias term times R i j ( 123 ) (Kuruvilla & Aghanim 2021). Based on the radial mean relative velocities between pairs in a triplet, we can introduce a new ratio statistic…”

“…We compare these constraints with those obtained from the mean pairwise velocity, and the mean relative velocity between pairs in a triplet as reported in Kuruvilla & Aghanim (2021). As a fair comparison, we use the constraints obtained from them using r min = 40 h −1 Mpc.…”

“…Mueller et al (2015) has shown that the mean pairwise velocity can utilised to constrain the summed neutrino mass, and has studied its interplay between the baryonic feedback and the summed neutrino mass effects at nonlinear separation scales. Furthermore the three-point mean relative velocity statistics is able to obtain stronger constraints on the summed neutrino mass when compared to the mean pairwise velocity (Kuruvilla & Aghanim 2021). However the growth rate measurement from the kSZ effect of the CMB are degenerate with the optical depth (e.g.…”

Cosmology with cosmic web environments I. Real-space power spectra

“…Other works make use of direct additional observables to the density field, such as the velocity, to improve the constraints on cosmological models and parameters (e.g. Mueller et al 2015;Kuruvilla & Aghanim 2021;Kuruvilla 2021).…”