some progresses on peculiar velocity cosmology zheng yi ( 郑逸 ) collaborators: pengjie zhang,...
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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”
9
• 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
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