Clustering%20of%20Luminous%20Red%20Galaxies%20and%20Applications%20to%20Cosmology

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Clustering of Luminous Red Galaxies and
Applications to Cosmology

• NicRoss (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
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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.

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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.

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What is the Universe made of?
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Baryonic matter
Dark Energy
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Dark matter
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Evidence from SNeIa, CMB, LSS, (Clusters)
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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).

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Motivation, observations vs. models

• Semi-Analytic Model predictions - lines, LRG
  Observations - stars z0.24 (L), z0.50 (R)
• Almedia et al. 2007 (astro-ph/0710.3557)

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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.

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Motivation

• 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

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

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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 0.4ltzlt0.8.
• Extended redshift arm led to photo-z calibration
• Proof of concept for future LRG studies e.g. BOSS

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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.

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

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LRG Photometric Selection, gri-bands

• Method Use SDSS photometry, gri-bands, to select
  intrinsically luminous (L gt 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.

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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 lt i lt 19.8
• 80 fields giving total area 180 degs2
• 92 spectroscopic completeness

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2dFGRS
SDSS LRG
2SLAQ
(P. Weilbacher)
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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.

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The 2 Point Correlation Function

• represents the excess probability of
  finding a PAIR of galaxies compared with a random
  distribution
• 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 r0, correlation length
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The 2 Point Correlation Function
a0 kms-1 ?0
a0 kms-1 ? 0.4
? (along the l.o.s.)
a500 kms-1 ?0
a500 kms-1 ? 0.4
? (perpendicular to the l.o.s.)

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

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The 2 Point Correlation Function

• Redshift-space, ?(s), and Real-space, ?(r), CFs
  related by ? (Kaiser 1987)
• Also, ? and ?M related (Peebles 1980 Lahav1991
  Peacock 2001 Hawkins 2003 Zehavi 2002)
• where b is the linear bias parameter, which
  is the ratio of galaxy to (underlying) mass
  fluctuations ?g b2 ?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. BlakeGlazebrook,
  2003 Tegmark 2006)

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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.

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2SLAQ LRG Redshift-space 2PCF

• 2SLAQ LRGs at redshift z 0.55, r07.45 /-
  0.35 h-1 Mpc
• SDSS LRGs (Zehavi et al. 2005) at z0.28,
  r09.80/-0.20 h-1 Mpc
• 2dFGRS Luminous Early-Type (Hawkins et al. 2003
  Norberg et al. 2002), at redshift z0.1, r06 h-1
  Mpc

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2SLAQ 2-D Correlation Function, ?(?,?)
? (along the l.o.s.)
? (perpendicular to the l.o.s.)
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Alcock-Paczynski Test

• 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 (AP, 1979 Ballinger,
  Peacock, Heavens 96 Popowski98 Hoyle02 da
  Angela05 KimCroft07)
• Pros Geometric test to determine ? no messy
  galaxy evolution v. complimentary to BAOs.
• Cons Peculiar velocities also affect isotropic
  structure.

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Cosmological Constraints
1.0

• Compare data to range of test cosmologies
• Degeneracy along ?M-?, recall
• Additional info e.g. ?(z0), 2dFGRS (Hawkins
  2003)
• ? 0.45
• ?M 0.25

?M(0)
0
0
1.0
0.10
?(z)
- 0.15
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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.

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Baryon Acoustic Oscillations

• In the tightly coupled baryon-photon fluid prior
  to Recombination, acoustic waves create a
  characteristic scale the sound horizon, RS.
• At Recombination, vs ? 0, wave stalls and the
  imprint of RS, (BAO), is frozen (but still
  evolves gravitationally) in the matter, and
  later, galaxy correlation functions.
• Rs(z1089) can be determined accurately with CMB
  (148 Mpc), so BAO become a very promising
  standard ruler, DA(z) and H(z).

• Wayne Hu, http//background.uchicago.edu/whu/
• Martin White, http//cdm.berkeley.edu/doku.php?id
  baopages

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Future LSS BAO LRG Projects

• What you need (minimum)
• Large volume of Universe (gt1 Gpc3)
• Large number of objects (105 - 106)
• Our Idea
• 300,000 LRG redshift surveyover
• 3,500 sq. degs. (95 deg-2)
• with redshift 0.5 lt z lt 1.0
• Requirements
• Imaging from SDSS and VST-ATLAS
• LRGs down to i lt 20.5 in 1 hour
• 4m-class telescope, reasonable site
• Multi-object spectrograph
• (Australian)

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AAOmega

• AAOmega, 392 fibre MOS, on 4m AAT
• Blue and Red arms
• 5600-8800Å ? 4000 Å _at_ z 0.4 - 1.2 (0.9).

• Large 200 night proposal
• Use LRGs to measure BAO at ltzgt0.7
• Pilot Program 03 Mar 2006 07 Mar 2006

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LRG riz-selection

• Again, use SDSS imaging
• Select in riz-bands, down to ilt20.5 (cf.
  2SLAQ ilt19.8)
• High stellar contamination, can do better
• Panels show selection areas and model tracks

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AAOmega LRG Pilot Run

• Mean redshift, ltzgt0.68
• Exposure times to get absorption line redshifts
  varied from 1 to 3 hours, (typically 1.67hrs)

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AAOmega LRG Correlation function

• wp(?) projection of 3-D ?(s)
• AAOmega LRG
• r0 9.03/-0.93
• AAOmega LRGs sample now comparable to SDSS LRGs
  for LSS studies
• However

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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.

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Baryon Oscillation Spectroscopic Survey

• PI David Schlegel, part of SDSS-III
• Use existing 2.5m telescope, upgrade optics and
  spectrographs
• 1.5x106 LRGs, 0.2ltzlt0.8 over 10,000 deg2
• 160,000 Ly? Forests from QSO sightlines,
  2.3ltzlt2.8, 8,000 deg2
• dA to 1, 1.1 and 1.5 at z0.35, 0.6, 2.5
• Due to start imaging in latter half 2008,
  spectroscopy 2009

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Conclusions

• 2SLAQ LRG Survey complete, gt13,000 LRG
  spectroscopic redshifts, 0.4 lt z lt 0.8.
• 2SLAQ LRGs have r07.45/-0.35 h-1 Mpc.
• Using dynamical (peculiar velocity) and geometric
  (Alcock-Paczynski) information find
  ?M0.250.10-0.15 and ?(z0.55)
  0.450.05-0.03
• Alcock-Paczynski test, v. complimentary to BAOs
• SDSS riz-band selection pushes ltzLRGgt0.7
• Future Projects, e.g. BOSS (LRG Ly?) Survey

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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.

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