# Presentation: 486721

**Clustering of Luminous Red Galaxies and Applications to Cosmology****_x0001_**

**Nic****_x0004_****Ross (Penn State) **
**Research Progress Meeting**
**LBNL**
**8th November 2007 **

**Ross et al., 2007, MNRAS, 381, 573**
**Ross et al., 2007, MNRAS submitted, astro-ph/0704.3739**
**Cannon et al., 2006, MNRAS, 372, 425**

## Slide 3

## Outline of talk

- Motivation
- The 2dF-SDSS LRG And QSO (2SLAQ) Survey
- Clustering techniques
- 2SLAQ LRG Clustering results and *z*-space distortions
- The AAOmega LRG Pilot Survey
- Future BAO Surveys, The B.O.S.S.

## Outline of talk

- Motivation
- The 2dF-SDSS LRG And QSO (2SLAQ) Survey
- Clustering techniques
- 2SLAQ LRG Clustering results and *z*-space distortions
- The AAOmega LRG Pilot Survey
- Future BAO Surveys, The B.O.S.S.

## ~70%

- ~26%

- 4%

- What is the Universe made of?

- Baryonic matter

**Dark matter**

- “Dark
- Energy”

**Evidence from: SNeIa, CMB, ****LSS****, (Clusters) **

## Motivation

- Luminous Red Galaxies (LRGs) provide a very good observational sample to test models of galaxy formation and evolution.
- Excellent tracers of Large Scale Structure (LSS).

## Semi-Analytic Model predictions - lines, LRG Observations - stars; z=0.24 (L), z=0.50 (R)
Almedia et al. 2007 (astro-ph/0710.3557)

- Almedia et al. 2007 (astro-ph/0710.3557)

- Motivation, observations vs. models

## Motivation

- Luminous Red Galaxies (LRGs) provide a very good observational sample to test models of galaxy formation and evolution.
- Excellent tracers of Large Scale Structure (LSS).
- 2 Point Correlation Function (2PCF) simple but powerful statistic.

## Eisenstein et al. 2005 (ApJ, 633, 560)

- `Bump’ in the 2 Point Correlation Function at ~100 *h**-1* Mpc
- Due to ``baryon acoustic oscillations’’
- Can be used as a Standard Ruler, determine geometry of the Universe

- Motivation

## Motivation

- Luminous Red Galaxies (LRGs) provide a very good observational sample to test models of galaxy formation and evolution.
- Excellent tracers of Large Scale Structure.
- 2 Point CF simple but powerful statistic.
- Redshift-space distortions can provide cosmological parameter constraints via Alcock-Paczyncski and clustering evolution (explained in due course)
- 2SLAQ extending SDSS LRGs to 0.4<z<0.8.
- Extended redshift arm led to photo-*z* calibration
- Proof of concept for future LRG studies e.g. BOSS

## Outline of talk

- Motivation
- The 2dF-SDSS LRG And QSO (2SLAQ) Survey
- Clustering techniques
- 2SLAQ LRG Clustering results and *z*-space distortions
- The AAOmega LRG Pilot Survey
- Future BAO Surveys, The B.O.S.S.

## SDSS DR6: 8417 deg2, 1,271,680 spectra, 790,860 gal

- SDSS DR6: 8417 deg2, 1,271,680 spectra, 790,860 gal

## LRG Photometric Selection, gri-bands

- Method: Use SDSS photometry, *gri-*bands, to select intrinsically luminous (*L > 3L**) red galaxies from   z0.0 to 0.8.
- Bruzual and Charlot (2003) evolutionary model tracks superimposed on the SDSS data.
- Star/galaxy separation from SDSS images. Some red M-type stars remain.

## 20’’

## Slide 16

## SDSS LRG vs. 2SLAQ LRG N(z)

- SDSS LRG sky density is 12 deg-2
- 2SLAQ LRG sky density is 53 deg-2
- Same populations, different redshifts
- 2SLAQ LRG Survey:
**13,121**** LRGs**
**17.5 < *****i***** < 19.8**
**80 fields giving total area ****180 degs****2**** **
**92% spectroscopic completeness**

## 2SLAQ

**(P. Weilbacher)**

**2dFGRS**

**SDSS LRG**

**2SLAQ**

## Outline of talk

- Motivation
- The 2dF-SDSS LRG And QSO (2SLAQ) Survey
- Clustering techniques
- 2SLAQ LRG Clustering results and *z*-space distortions
- The AAOmega LRG Pilot Survey
- Future BAO Surveys, The B.O.S.S.

## The 2 Point Correlation Function

- Power Law behaviour:
- Measure the *redshift**-space* CF          which include peculiar velocities due to cluster infall and random motions leading to “redshift-space distortions”.
- Can measure ****** in two dimensions,                with        ***,* perpendicular and , parallel, to line-of-sight where,       		          and effects of *z*-space distortions seen

- , slope
*r**0*, correlation length

## Hawkins et al. (2003, MNRAS, 346, 78)

***a*****=0 ****kms****-1**
********=0**

***a*****=****500 kms****-1**
********=0**

***a*****=0 ****kms****-1**
******** ****=0.4**

***a*****=****500 kms****-****1**
******** ****=0.4**

- The 2 Point Correlation Function

****** ****(perpendicular to the l.o.s.)**

****** ****(along the l.o.s.)**

## The 2 Point Correlation Function

- Also, ** and M related (Peebles 1980; Lahav_x0004_1991; Peacock+ 2001; Hawkins+ 2003; Zehavi+ 2002)
-     where *b* is the `linear bias parameter’, which is the ratio of galaxy to (underlying) mass fluctuations; ***g** = b**2** ****m*
- This linear bias, *b*, important because it reduces the fractional error due to shot noise, i.e. *b **,* no. of objects needed  (e.g. Blake&Glazebrook, 2003; Tegmark 2006)

## Outline of talk

- Motivation
- The 2dF-SDSS LRG And QSO (2SLAQ) Survey
- Clustering techniques
- 2SLAQ LRG Clustering results and *z*-space distortions
- The AAOmega LRG Pilot Survey
- Future BAO Surveys, The B.O.S.S.

## 2SLAQ LRG Redshift-space 2PCF

- 2SLAQ LRGs at redshift *z *= 0.55,  *r**0*=7.45 +/- 0.35 *h**-1* Mpc
- SDSS LRGs  (Zehavi et al. 2005) at *z*=0.28,  *r**0*=9.80+/-0.20 *h**-1* Mpc
- 2dFGRS Luminous Early-Type (Hawkins et al. 2003; Norberg et al. 2002), at redshift z≈0.1, *r**0*≈6 *h**-1* Mpc

## 2SLAQ 2-D Correlation Function, (,)

- 2SLAQ 2-D Correlation Function, ******(********,********)**

****** **(perpendicular to the l.o.s.)

**** (along the l.o.s.)

## Ratio of observed radial size to 
  angular size, varies with cosmology:              

Have an intrinsically isotropic structure (e.g. the clustering of galaxies) and observe the radial/angular ratio (A&P, 1979; Ballinger, Peacock, Heavens ’96; Popowski+’98; Hoyle+’02; da Angela+’05; Kim&Croft+’07)
Pros: Geometric test to determine ; no messy galaxy evolution; v. complimentary to BAOs. 
Cons: Peculiar velocities also affect isotropic structure. 

-   angular size, varies with cosmology:
- Have an intrinsically isotropic structure (e.g. the *clustering* of galaxies) and observe the radial/angular ratio (A&P, 1979; Ballinger, Peacock, Heavens ’96; Popowski+’98; Hoyle+’02; da Angela+’05; Kim&Croft+’07)
- Pros: Geometric test to determine ****; no messy galaxy evolution; v. complimentary to BAOs.
- Cons: Peculiar velocities also affect isotropic structure.

- Alcock-Paczynski Test

## Compare data to range of test cosmologies
Degeneracy along M-, recall 

Additional info: e.g. (z=0), 2dFGRS (Hawkins+ 2003)
 = 0.45

M =0.25 

- Compare data to range of test cosmologies
- Degeneracy along M-, recall
- Additional info: e.g. **(z=0), 2dFGRS (Hawkins+ 2003)
****** ****= 0.45**
******M ****=0.25 **

******M(0)**

*****(z)*

**1.0**

**0**

**0**

**1.0**

- Cosmological Constraints

- +0.10

- - 0.15

## Outline of talk

- Motivation
- The 2dF-SDSS LRG And QSO (2SLAQ) Survey
- Clustering techniques
- 2SLAQ LRG Clustering results and *z*-space distortions
- The AAOmega LRG Pilot Survey
- Future BAO Surveys, The B.O.S.S.

## Baryon Acoustic Oscillations

- In the tightly coupled baryon-photon fluid prior to Recombination, *acoustic waves* create a characteristic scale – the sound horizon, *R*S.
- At Recombination, *v*s  0, wave stalls and the imprint of *R*S, (BAO), is frozen (but still evolves gravitationally) in the matter, and later, galaxy correlation functions.
*R**s**(z*=1089*)* can be determined accurately with CMB (148 Mpc), so BAO become a very_x0001_ promising standard ruler, *D**A**(z)* and *H(z)**.*

- Wayne Hu, http://background.uchicago.edu/~whu/
- Martin White, http://cdm.berkeley.edu/doku.php?id=baopages

## Future LSS BAO LRG Projects

- What you need (minimum):
**Large ****volume**** of Universe (>1 Gpc****3****)**
**Large ****number**** of objects   (10****5**** - 10****6****)**
- Our Idea:
**~300,000 ****LRG redshift survey****_x0004_****over**** **
**~3,500 sq. degs****. (95 deg****-2****) **
** ****with redshift**** 0.5 < *****z *****< 1.0**
- Requirements:
**Imaging**** from SDSS and VST-ATLAS**
**LRGs down to *****i *****< 20.5**** in ~1 hour **
**4m-class telescope, reasonable site***** ***
**Multi-object spectrograph**
**(****Australian****)**

## AAOmega

- AAOmega, 392 fibre MOS, on 4m AAT
- Blue and Red arms
- 5600-8800Å  4000 Å @        *z *= 0.4 - 1.2 (~0.9).

- `Large’ ~200 night proposal
- Use LRGs to measure BAO at <z>=0.7
- Pilot Program 03 Mar 2006 – 07 Mar 2006

## LRG riz-selection

- Again, use SDSS imaging
- Select in *riz*-bands, down to *i*<20.5       (cf. 2SLAQ *i*<19.8)
- High stellar contamination, can do better
- Panels show selection areas and model tracks

## AAOmega LRG Pilot Run

- Mean redshift, <*z*>=0.68
- Exposure times to get absorption line redshifts varied from 1 to 3 hours, (typically 1.67hrs)

## AAOmega LRG Correlation function 

-  *w**p**(****)*  projection of 3-D ***(s)*
-  **AAOmega LRG **
***r******0***** = 9.03+/-0.93**
** **AAOmega LRGs sample now comparable to  SDSS LRGs for LSS studies
-  However...

## Outline of talk

- Motivation
- The 2dF-SDSS LRG And QSO (2SLAQ) Survey
- Clustering techniques
- 2SLAQ LRG Clustering results and *z*-space distortions
- The AAOmega LRG Pilot Survey
- Future BAO Surveys, The B.O.S.S.

## Baryon Oscillation Spectroscopic Survey

- PI: David Schlegel, part of “SDSS-III”
**Use existing 2.5m telescope, ****upgrade optics and spectrographs**
**1.5x10****6**** LRGs****, 0.2<*****z*****<0.8 over 10,000 deg****2**
**160,000 ****Ly******** Forests**** from QSO sightlines, 2.3<*****z*****<2.8, 8,000 deg****2**
*d**A** *to 1, 1.1 and 1.5% at z~0.35, 0.6, 2.5
**Due to start ****imaging in latter half 2008, spectroscopy 2009**** **

## Conclusions

- 2SLAQ LRG Survey complete, >13,000 LRG spectroscopic redshifts, 0.4 < *z **	*< 0.8.
- 2SLAQ LRGs have *r**0*=7.45+/-0.35 h-1 Mpc.
- Using dynamical (peculiar velocity) and geometric (Alcock-Paczynski) information find: _x0018_M=0.25+0.10-0.15 and _x0016_***(z*=0.55*) = 0.45*+0.05-0.03_x0003_
- Alcock-Paczynski test, v. complimentary to BAOs
- SDSS *riz*-band selection pushes <*z**LRG*>=0.7
- Future Projects, e.g. BOSS (LRG & Ly) Survey

## Credits

- Tom Shanks, Jose da Angela, Phil Outram, Alastair Edge, David Wake (Durham)
- Bob Nichol (Portsmouth)
- Russell Cannon, Scott Croom, Rob Sharp (AAO)
- Michael Drinkwater, Isaac Roseboom, Kevin Pimbblet (UQ)
- Daniel Eisenstein (Arizona)
- John Peacock (Edinburgh)
- And Nikhil P. and Martin W. for inviting me.

## Slide 39

## Slide 40