# Presentation: 925142

## Cross-correlation of WMAP 3rd year and SDSS DR4: 

**new evidence for dark energy**

- Anna Cabre, Enrique Gaztañaga, Pablo Fosalba, Marc Manera, Francisco Castander
- astro-ph/0603690

## Motivation:

- Obtain dark energy from the ISW effect crosscorrelating CMB and LSS
**Summary**
- Integrated Sachs Wolfe effect background
- Large scale structure data and CMB data
- Analysis, errors...
- Results
- Conclusions and Future

## Integrated Sachs Wolfe effect

**Integrated Sachs Wolfe effect**
- ISW is the gravitational redshift that photons coming from CMB undergo when they fall in a deep potential and come out from a smoother one.
- This change in potential can be created by curvature or by dark energy. Assuming that the universe is flat (from WMAP results), ISW indicates the existence of dark energy.

## How to detect ISW?   

- Temperature fluctuations created by ISW are difficult to see in power spectrum, and the results seem to supress that

- Wayne Hu

- Alternative:
**Cross correlating CMB temperature with potential traced by LSS**
- (Crittenden & Turok 1996)

##  CMB data

-  **CMB data**

**LSS data**

-      WMAP 3rd year

-          SDSS DR4

- -5200 sq deg (13% sky)
- -Selection of subsamples with different redshift distribution
- -3 magnitude subsamples with r=18-19, r=19-20 and r=20-21 with  106 – 107 galaxies
- -high redshift Luminous Red Galaxy (Eisentein et al. 2001)
- -Mask avoids holes, trails, bleeding, bright stars and seeing>1.8

- V-band (61 Hz)
- HEALPix tessellation
- Kp0 mask

## ISW in equations...

**ISW in equations...**

- Limber approximation

## wGG(q) a b2s82 f(Wm)

- wGG(q) a b2s82 f(Wm)
- wTG(q) a b s82 g(Wm)
- b  s8from GG
-  x s8  from WMAP
- TG factor  b s82 fix

##              b s8

- +deep
- +magnitude

- + bias

- Slices with more S/N
-              b s8
- 20-21  0.90-0.96
- LRG   1.02-1.12

**Autocorrelation results (galaxy-galaxy)**

## GG fitting for slice 20-21

- GG fitting for slice high redshift

## Jack-knife errors

** ****c****2**** ****distribution**

**Singular Value Decomposition (SVD)**

- Redshift selection function

- r=20-21   zc=0    z0=0.2     zm=0.3
- LRG   zc=0.37    z0=0.45   zm=0.5

- 20-21

- LRG

## r=20-21     S/N=3.6

- LRG     S/N=3.

- S/N total=4.7

## signal to noise picture...

- Covarianca matriu per DR4 2021 o 8888

- Covarianca matriu simulacions MC

- Covariance for JK

- Covariance for MC

## For a flat universe, 

- For a flat universe,
- with bias, sigma8 and w=-1 fix....
- dark energy must be...

- 68%  0.80-0.85

- 95%  0.77-0.86

## Can we obtain information about w?

- Contour:
- 1, 2 sigma
- 1 dof

## Errors JK, reliable??

**38 JK**

**76 JK**

**76 JK**

**38 JK**

**CORRELACIÓ GG**

**CORRELACIÓ TG**

**Errors JK, reliable??**

## 1000 simulations of galaxies and temperature fluctuations with ISW

## Slide 17

## Conclusions:

**·There is no change of the ISW detection from WMAP1 to WMAP3**
**·To improve we need to sample a larger area (SDSS DR5) or larger volume (DES) and more slices...**

## ·GG prefers higher omega matter than TG,  signal TG too high.. why?

**·GG prefers higher omega matter than TG,  signal TG too high.. why?**
**·We can not break the degeneracy between ****W****L**** and w with ISW and fsky=0.13**

- Dark Energy Survey predictions...