Some progresses on peculiar velocity cosmology Zheng Yi ( 郑逸 ) Collaborators: Pengjie Zhang, Yipeng Jing, Weipeng Lin, Jun Pan, Yong-Seon Song P. Zhang, J. Pan, and Y. Zheng, Phys. Rev. D 87, (2013), Y. Zheng, P. Zhang, Y. Jing, W. Lin, and J. Pan, Phys. Rev. D 88, (2013), P. Zhang, Y. Zheng, Y. Jing, Y. Zheng, P. Zhang, Y. Jing, Y. Zheng, P. Zhang, Y. Jing,

outline Peculiar velocity decomposition which facilitate RSD modeling Window function Higher order correction Rigorous FOG effect Peculiar velocity reconstruction Determination of large scale volume weighted halo velocity bias in simulations Key point we could measure volume weighted velocity field accurately from simulaitons ： For 1200Mpc, 1024^3 simulation, convergence test, accurate until k~0.3h/Mpc For halos, we correct the sampling artifact at 1% accuracy until k~0.1h/Mpc Future work: k\mu dependence of residual redshift space power spectrum MG halo velocity bias?

Velocity decomposition Background from Wang et al rotational component irrotational component Zhang et al

A new RSD formulae 2. Physical FOG: dispersion, NG 2. Physical FOG: dispersion, NG Zhang et al , Zheng et al Determin ed by W(k)!

Zheng et al

The cumulant expansion Gaussian approximation works! Zheng et al Break the degeneracy?

Velocity bias: potential systematic error 7 A first order systematic error in cosmology – Have to understand the velocity bias to 1% level accuracy at k~0.1h/Mpc. THCA, From PJ’s PPT

8 Peculiar velocity cosmology by default assumes no velocity bias at large scale: Environmental effect: halos/galaxies locate at special regions around density peaks. Proto-halos/linearly evolved density peaks (BBKS 1986; Desjacques & Sheth 2010) have velocity bias What would be the velocity bias of halos in simulations? THCA, From PJ’s PPT

Severe sampling artifact can be misinterpreted as a “velocity bias” 9 Naive comparison between the raw measurements of halo velocity and DM velocity gives a apparent b v <1 Illusion caused by the sampling artifact Unphysical numerical effect. But can be misinterpreted as a “velocity bias” Zheng, ZPJ, Jing, 2014b DM Halo THCA, Yipeng’s P 3 M simulation: 1200 Mpc/h, particles From PJ’s PPT

THCA, Sampling artifact: theory vs. simulation From PJ’s PPT

1. Velocity bias vanishes at k 0.1h/Mpc? Poses a challenge 11 THCA, From PJ’s PPT

Future plans Test our RSD model with simulation – Monopole, quadruple… – 2D analysis Use our model to analyze BOSS data Halo velocity bias under modified gravity – Could be smoking guns of MG – Promising tests of the equivalence principle …. THCA,