Abstract
We explored the impact of baryonic effects (namely stellar and active galactic nuclei feedback) on the moments of pairwise velocity using the Illustris-TNG, EAGLE, cosmo-OWLS, and BAHAMAS suites of cosmological hydrodynamical simulations. The assumption that the mean pairwise velocity of the gas component follows that of the dark matter is studied here at small separations, and we find that even at pair separations of 10–20h−1Mpc, there is a 4–5% velocity bias. At smaller separations, it gets larger with varying strength depending on the sub-grid prescription. By isolating different physical processes, our findings suggest that the large-scale velocity bias is mainly driven by stellar rather than active galactic nuclei feedback. If unaccounted for, this velocity offset could possibly bias cosmological constraints from the kinetic Sunyaev-Zel’dovich effect in future cosmic microwave background (CMB) surveys. Furthermore, we examined how the first and the second moment of the pairwise velocity are affected by both the baryonic and the neutrino free-streaming effects for both the matter and gas components. For both moments, we were able to disentangle the effects of baryonic processes from those of massive neutrinos; and for pair separations below 20h−1Mpc, we find that these moments of the pairwise velocity decrease with increasing neutrino mass. Our work thus sets out a way in which the pairwise velocity statistics can be utilised to constrain the summed mass of neutrinos from future CMB surveys and peculiar velocity surveys.
Highlights
Over the last decade or so, cosmology has evolved to a state where we are able to precisely constrain the cosmological parameters with the help of galaxy redshift surveys, gravitational lensing surveys (e.g. Heymans et al 2020), and cosmic microwave background (CMB) experiments (e.g. Planck Collaboration VI 2020)
We focused on the imprint of baryons and neutrinos on the first two moments of the radial pairwise velocity distribution
The assumption that the mean pairwise velocity of gas component follows that of the dark matter is a crucial one undertaken in kinetic Sunyaev-Zeldovich (kSZ) analyses
Summary
Over the last decade or so, cosmology has evolved to a state where we are able to precisely constrain the cosmological parameters with the help of galaxy redshift surveys (e.g. eBOSS Collaboration 2020), gravitational lensing surveys (e.g. Heymans et al 2020), and cosmic microwave background (CMB) experiments (e.g. Planck Collaboration VI 2020). In addition to clustering statistics, the onepoint probability distribution function of the total matter has been shown to be sensitive to neutrino mass and could provide strong constraints (Uhlemann et al 2020) In this era of precision cosmology, it is important to consider the effects of baryons and processes associated with galaxy formation (e.g. cooling and feedback) on cosmological observables, as we push the analyses to smaller, “non-linear” scales. It has been shown that the mean radial pairwise velocity measured from the kSZ effect is capable of constraining alternative theories of gravity and dark energy (Bhattacharya & Kosowsky 2007, 2008; Kosowsky & Bhattacharya 2009; Mueller et al 2015a), in addition placing constraints on the summed mass of neutrinos (Mueller et al 2015b).
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