Some progresses on peculiar velocity cosmology Zheng Yi ( 郑逸 ) Collaborators: Pengjie Zhang,...

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, 063526 (2013), 1207.2722.Y. Zheng, P. Zhang, Y. Jing, W. Lin, and J. Pan, Phys. Rev. D 88, 103510 (2013),

1308.0886P. Zhang, Y. Zheng, Y. Jing, 1405.7125Y. Zheng, P. Zhang, Y. Jing, 1409.6809Y. Zheng, P. Zhang, Y. Jing, 1410.1256

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. 2012

𝑽 (𝒙)rotational component

𝑽 𝑩=𝑽 (𝒌 )−𝑽 𝑬

irrotational component

𝑽 𝑬=[𝑽 (𝒌 ) ∙ �̂�]�̂�

𝜃 (𝒌 )=𝑖𝒌∙𝑽 𝑬 (𝒌)/𝐻

correlated with

𝜃𝛿(𝑘)=𝛿 (𝑘 )𝑊 (𝑘)

uncorrelated with

𝜃𝑆 (𝑘 )=𝜃 (𝑘 )−𝜃𝛿

Zhang et al. 1207.2722

𝑽 𝛿 𝑽 𝑆𝑽 𝐵

A new RSD formulae 1.Underestimation of by

2. Physical FOG: dispersion, NG

Zhang et al. 1207.2722, Zheng et al. 1308.0886

3.Determined by W(k)!

Window function I

𝜃= 𝑓 𝛿 underestimation

Zheng et al. 1308.0886

The cumulant expansion

Gaussian approximation works!

Zheng et al. 1308.0886

contributesmost to the FOG effect.

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, 2014.10.9From 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, 2014.10.9From PJ’s PPT

Severe sampling artifactcan be misinterpreted as a “velocity bias”

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• Naive comparison between the raw measurements of halo velocity and DM velocity gives a apparent bv<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, 2014.10.9

Yipeng’s P3M simulation: 1200 Mpc/h, 10243 particles

From PJ’s PPT

THCA, 2014.10.9 10

Sampling artifact: theory vs. simulation

From PJ’s PPT

1. Velocity bias vanishes at k<0.1 h/Mpc. Consolidates peculiar velocity cosmology2. Velocity bias at k>0.1h/Mpc? Poses a challenge

11THCA, 2014.10.9

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, 2014.10.9 12