Redshift space distortion and halo velocity bias ZHENG Yi ( ) - - PowerPoint PPT Presentation

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redshift space distortion and halo velocity bias
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Redshift space distortion and halo velocity bias ZHENG Yi ( ) - - PowerPoint PPT Presentation

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(Cosmological group at KASI) http://cosmology.kasi.re.kr/ Redshift space distortion and halo velocity bias ZHENG Yi ( ) Zheng, Yong, Oh, et al., 2015, in preparation Zhang, Zheng & Jing, 2014, arXiv: 1405.7125, PRD accepted Zheng,

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Redshift space distortion and halo velocity bias

ZHENG Yi (郑逸)

Zheng, Yong, Oh, et al., 2015, in preparation Zhang, Zheng & Jing, 2014, arXiv: 1405.7125, PRD accepted Zheng, Zhang & Jing, 2014a, arXiv: 1409.6809, PRD accepted Zheng, Zhang & Jing, 2014b, arXiv: 1410.1256, PRD accepted

(Cosmological group at KASI) http://cosmology.kasi.re.kr/

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Outline

  • Redshift space distortion
  • Key question: if the velocity dispersion

in the FoG

term is scale independent or not?

  • Scoccimarro model
  • TNS model
  • Halo velocity bias
  • Theoretical prediction from Gaussian statistics ( scale

dependence)

  • Measurement from simulation ( = 1 at ≤

0.1 ℎ/Mpc in 2% accuracy)

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Introduction

  • A. J. S. Hamilton, astro-ph/9708102

Observationally:

Euclid, BigBOSS

et all:

O(1%) 5-10%

Theoretically:

  • 1. Nonlinear mapping
  • 2. Nonlinear evolution
  • 3. Bias modelling

Torre & Guzzo, 1202.5559

The redshift position s: = + () ⁄

  • = + ()

⁄

  • Reid et al. 2012
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Phenomenological RSD model

arXiv:1506.05814v1 interpreted to be global (pairwise) velocity dispersion, a constant fitting parameter (?) Taruya et al. arXiv:1006.0699

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1.

is k dependent

  • 2. Not physical
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Mathematically show the point: scoccimarro’s model For each bin, we restrict to < 0.1, and fit the

.

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RegPT: Taruya et al. PHYSICAL REVIEW D 86, 103528

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Taruya’s model

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Perturbation:

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Test of A, B terms

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simulation

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Further improvment

  • C term: velocity correlation
  • Zhang13 model. (P. Zhang, J. Pan, and Y. Zheng,

1207.2722.)

Taruya et al. arXiv:1006.0699

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Velocity bias or not?

A fundamental problem in peculiar velocity cosmology

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Cosmological observations: galaxy velocity field (power spectrum) Cosmological observations: dark matter velocity field (power spectrum) In linear theory: Desjacques & Sheth 0909.4544

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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?

PJZ’s PPT

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Truth is:

YongPyong-High1 2015 22

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The sampling artifact

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  • Velocity field from most RSD models is volume

weighted

  • Where there is no particle, the velocity is usually

non-zero. It can be large. The sampling on the volume weighted velocity field is biased/imperfect

  • The sampling artifact: inevitable for

inhomogeneously distributed objects. Severe for sparse populations. Persists for NP, Voronoi and Delaunay tessellation.

  • The sampling and the signal are neither

completely uncorrelated nor completely

  • correlated. Hard to correct straightforwardly
  • Can be fully described in the language of the D

field (ZPJ, Zheng & Jing, 2014), similar to CMB lensing

?

PJZ’s PPT

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Severe sampling artifact

can 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

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

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Understanding the sampling artifact

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Including the correlation in D.Not exact. Neglect correlation in D Neglect v-D correlation.

  • Our model works.
  • But improvements are needed
  • Take correlation in D fully into account
  • Take v-D correlation into account

Zheng, ZPJ & Jing, 2014a ZPJ, Zheng & Jing, 2014 PJZ’s PPT

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Theory and simulation of the sampling artifact

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Theory prediction: ZPJ, Zheng & Jing, 2014 Simulation verification Zheng, ZPJ & Jing, 2014a

The measured velocity power spectrum The real velocity power spectrum

ZPJ’s PPT

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Sampling artifact: theory vs. simulation

1% accuracy <0.1h/Mpc 1% accuracy <0.1h/Mpc

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Raw measurement Step two correction Step one Correction

ZPJ’s PPT

YongPyong-High1 2015

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  • 1. Velocity bias vanishes at k<0.1 h/Mpc. Consolidates

peculiar velocity cosmology

  • 2. Velocity bias at k>0.1h/Mpc? Poses a challenge

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ZPJ’s PPT

YongPyong-High1 2015

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For discussions

  • Needs theory explanation
  • Needs more accurate quantification

– Need improved understanding of the sampling artifact

  • Needs to extend to galaxies (mock catalog)
  • Perhaps needs new velocity assignment (e.g. Jun

Zhang’s idea)

  • Cosmological applications

– Could be smoking guns of MG – Promising tests of the equivalence principle (ongoing work with Zheng Yi, Yipeng, Baojiu Li & De-Chang Dai)

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ZPJ’s PPT

YongPyong-High1 2015