The effect of baryons on redshift space distortions and cosmic density and velocity fields in the EAGLE simulation
Abstract
We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) galaxy formation simulation to study the effects of baryons on the power spectrum of the total matter and dark matter distributions and on the velocity fields of dark matter and galaxies. On scales k ≳ 4 h Mpc^{1} the effect of baryons on the amplitude of the total matter power spectrum is greater than 1 per cent. The backreaction of baryons affects the density field of the dark matter at the level of ∼3 per cent on scales of 1 ≤ k/( h Mpc^{1}) ≤ 5. The dark matter velocity divergence power spectrum at k ≲ 0.5 h Mpc^{1} is changed by less than 1 per cent. The 2D redshift space power spectrum is affected at the level of ∼6 per cent at k≳ 1 h Mpc^{1} (for μ > 0.5), but for k≤ 0.4 h Mpc^{1} it differs by less than 1 per cent. We report vanishingly small baryonic velocity bias for haloes: the peculiar velocities of haloes with M_{200} > 3 × 10^{11} M_{⊙} (hosting galaxies with M_{*} > 10^{9} M_{⊙}) are affected at the level of at most 1 km s^{1}, which is negligible for 1 per centprecision cosmology. We caution that since EAGLE overestimates cluster gas fractions it may also underestimate the impact of baryons, particularly for the total matter power spectrum. Nevertheless, our findings suggest that for theoretical modelling of redshift space distortions and galaxy velocitybased statistics, baryons and their backreaction can be safely ignored at the current level of observational accuracy. However, we confirm that the modelling of the total matter power spectrum in weak lensing studies needs to include realistic galaxy formation physics in order to achieve the accuracy required in the precision cosmology era.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 September 2016
 DOI:
 10.1093/mnrasl/slw081
 arXiv:
 arXiv:1603.03328
 Bibcode:
 2016MNRAS.461L..11H
 Keywords:

 galaxies: haloes;
 cosmology: theory;
 dark matter;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 5 pages, 2 figures, accepted for publication in MNRSL, figure 1 updated for readability, figure 2 changed (include now P^2(mu) at fixed k). Conclusions unchanged