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The 8 th Sino – German workshop Teppei O KUMURA (SHAO) PowerPoint Presentation

The 8 th Sino – German workshop Teppei O KUMURA (SHAO)

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### Intrinsic ellipticity correlation of luminous red galaxies and misalignment with their host dark matter halos

The 8th Sino – German workshop

Teppei OKUMURA (SHAO)

Collaborators: Yipeng Jing (SHAO) & Cheng Li (MPA)

References:

Okumura, Jing, & Li, ApJ, 694, in press (arXiv:0809.3790) Okumura & Jing, ApJL, accepted (arXiv:0812.2935)

Tidal field, … galaxies and misalignment with their host dark matter halos

Introduction- Weak gravitational lensing by large-scale structure
- Directly probe the matter distribution

- Observable
- Ellipticity of galaxies eobs

true

observed

eobs

es

- Intrinsic ellipticity – ellipticity (II) correlation can be a contamination for weak lensing observations.

SDSS luminous red galaxies (LRG) galaxies and misalignment with their host dark matter halos

- Properties of LRGs
- Giant ellipticals (not contaminated by spirals)
- Almost all the LRGs are central galaxies (~ 95%)
- LRGs preferentially reside in massive halos which have stronger ellipticity correlation (Jing2002).

- We use 83,773 LRGs at 0.16 < z < 0.47 and –23.2 < Mg < –21.2 from the SDSS DR6 sample.

Measuring the II correlation galaxies and misalignment with their host dark matter halos

β

- Definitions
- Ellipticity of galaxies
- II correlation function
- c22 is calculated in the same way and cross-correlations, c12 and c21, should vanish on all scales.

axis ratio

orientation

= 0 : line = 1 : spherical

q = a / b

- Stronger correlations can be seen in the brighter sample although the error bars are large.

Bright sample

- Positive c11 on small scales
- Brighter LRGs tend to reside in more massive halos
- More massive halos have stronger ellipticity correlations (Jing2002).

Faint sample

Halo occupation distribution for LRGs (Seo+2008, Zheng+) although the error bars are large.

Galaxies assigned

N(M)=Ncen(M)+Nsat(M)

- Mock LRG catalog
- Then modeled ellipticity correlation functions can be calculated.

- Mock halo catalog from N-body simulation (Jing et al. 2007)
- Concordance LCDM model was assumed
- Ellipticity of each halo is computed by tracing all the particles in the halo.

Jing & Suto (2000)

Comparison of observation with model although the error bars are large.

4 times smaller

- First we assume that all central LRGs are completely aligned with their host halos.
- There are significant discrepancies in the amplitude between observation and model.

Model

Observation

- We will model the II correlation by considering the misalignment of central LRGs with their host halos.

Misalignment between central LRGs and their host halos although the error bars are large.

- Misalignment angle parameter σθ
- Assumption that the PDF of the misalignment angle θ follows Gaussian,

Calculation of model c11(r ;σθ) for LRGs

θ

Δc11(r ;σθ) = c11model(r ;σθ) – c11obs(r)

Observation although the error bars are large.

σθ = 0 model

σθ = 35 model

Constraints on misalignment- A model which the central galaxies and their host halos are completely aligned is strongly rejected by our analysis.

Implications for weak lensing surveys although the error bars are large.

Dependence of II correlation on halo mass (Jing 2002)

- An example
- CFHTLS weak lensing survey (zs ~ 1 and RAB=24.5). (Fu+)
- Central galaxies in the DEEP2 are in dark halos ~ 4×1011h–1 Msun (Zheng+)

- If these central galaxies have the same misalignment distribution as the SDSS LRGs, the II correlation can contribute by 5 – 10% to the shear correlation.

Hirata & Seljak (2004), Pengjie’s talk although the error bars are large.

Distant source (G)

Nearby source (I)

GI terms

Another contamination; Gravitational shear – intrinsic ellipticity correlation- Observables
- Ellipticity of galaxies

- Unlike II correlation, GI correlation can exist between galaxies at very different redshifts.

shear

II

Measuring the GI correlations although the error bars are large.

β

- Definitions
- Ellipticity of galaxies
- Projected GI correlation function
- In observation

Directly related to the GI term of the shear power spectrum.

This relation is indeed valid on large scales.

Galaxy biasing ~2 for LRGs

The GI correlation functions of LRGs in observation and in LCDM model

- The GI correlation is better determined than the II correlation in observation.
- The GI correlation can be well modeled in the current LCDM model if the misalignment angle parameter follows

Correlation of the LRG shape and orientation

- Normalized GI correlation function
- If there is no correlation
between q and β, we expect

- If there is no correlation

axis ratio

orientation

conclusions LCDM model

- II correlation
- The correlation was determined up to 30h–1Mpc.
- Luminosity dependence was also detected.
- We constrained the misalignment parameter
- If not corrected, the II correlation can lead to contamination at 5~10% levels to cosmic shear.

- GI correlation
- The correlation was also measured accurately.
- By comparing with a simulation,we found the GI correlation can be well modeled in the current LCDM model if the misalignment angle
- We found a correlation between the axis ratios and orientations of LRGs which amplifies the GI correlation by ~15 %.

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