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**Cosmological Constraints from Baryonic Acoustic Oscillations**

Carlton Baugh Institute for Computational Cosmology Durham University Unity of the Universe Portsmouth 30th June 2009

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**Outline: cosmology from BAO**

BAO: the basics BAO: in practice Constraining dark energy: the next steps

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BAO: the basics (Wayne Hu) (Daniel Eisenstein) Oscillations in photon-baryon fluid: pressure vs gravitational instability Sound wave propagates until decoupling of matter and radiation Maximum wavelength is horizon scale at decoupling

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**The BAO signal RADIATION MATTER Divide matter spectrum by**

First predicted by Peebles & Yu 1970, Zeldovich 1970 Clear peaks in radiation spectrum Peaks out of phase between Cl and P(Kk) Reduced amplitude in matter P(k) BAO scale related to sound horizon at recombination Considered as a standard ruler RADIATION MATTER Divide matter spectrum by Featureless reference to Emphasize BAO signal Meiksin, White & Peacock 1999

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**Relating BAO standard ruler to cosmological parameters**

BAO scale is approx. Standard ruler Radial measurement gives H(z) Perpendicular measurement gives angular diameter distance Sound horizon scale known from CMB (David Schlegel)

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**Relating BAO to cosmological parameters**

Sound horizon: (Eisenstein & Hu 1998) (baryon density) (matter density) Constrain : H(z) – expansion history – dark energy equation of state angular diameter distance – dark energy eqn of state matter density baryon density

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**Detection of BAO Eisenstein et al 2005 47,000 SDSS LRGs 0.72 cubic Gpc**

Constraint on spherically averaged BAO scale Constrain distance parameter: Angular diameter distance Hubble parameter

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**Detection of BAO Best fit Linear theory Convolved with Survey window**

function Cole et al dFGRS main galaxy sample

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**How well do we need to measure BAO?**

Hold other cosmological parameters fixed dw ~ 7 ds (z=3) dw ~ 4 ds (z=1) Dark energy equation of state Angulo et al distance scale measurement

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**How well do we need to measure BAO?**

s/Da held fixed dw ~ 2 ds (z=3, z=1) Dark energy equation of state Angulo et al distance scale measurement

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**BAO data: recent snapshot**

Percival et al 2007 Joint analysis of 2dFGRS, SDSS main, SDSS LRG For a flat universe and constant w, using WMAP s and SNLS data:

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**BAO data: recent snapshot**

Measurement of spherically averaged BAO constrains: BAO data give: BAO by themselves favoured w<-1 SNe data suggest distance ratio 2.6 sigma away from this. Percival et al

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**Modelling the BAO signal**

Proof of concept work used linear perturbation theory: Blake & Glazebrook 2003; Glazebrook & Blake 2005; Haiman & Hu 2003 Extended/Renormalised Perturbation theory: Smith et al; Komatsu et al. Simulations: Seo & Eisenstein 2003, 2007, Huff et al.; Takahasi et al 2009; Smith et al 2007; Smith/Sheth/Scoccimarro

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**The evolution of BAO Dark matter Sample variance in 500/h Mpc box**

galaxies Springel et al. 2005

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**Baryonic Acoustic Simulations at the ICC BASICC**

L = 1340/h Mpc V=2.4/h^3 Gpc^3 (20 x Millennium volume) N=1448^3 (>3 billion particles) Can resolve galactic haloes 130,000 hours CPU on Cosmology Machine Combine with semi-analytical galaxy formation model GALFORM 50 low-res BASICC runs for errors (= 1000 Millenniums!) Angulo et al. 2008

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**Combine with galaxy formation model**

H-alpha emitters z=1 H-band selection Alvaro Orsi et al. 2009

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**Distortions to the BAO signal**

Nonlinear growth of fluctuations Angulo et al. 2008

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**Distortions to the BAO signal**

Nonlinear growth of fluctuations Redshift space distortions Angulo et al. 2008

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**Distortions to the BAO signal**

Remove asymptotic bias: Scale dependent halo bias Angulo et al. 2008

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**Distortions to the BAO signal**

Scale dependent galaxy bias Angulo et al. 2008

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**Distortions to the BAO signal**

Nonlinear growth of fluctuations Redshift space distortions Scale dependent halo and galaxy bias Angulo et al. 2008

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**Extracting the BAO signal**

Define reference spectrum from measurement Percival et al 2007 Angulo et al 2008

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**An improved fitting method**

Percival et al 2007: Define reference Spectrum from measured P(k) “De-wiggle” linear theory model to damp higher harmonic oscillations BLUE: Blake & Glazebrook RED: linear theory, dewiggled

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**Extracting the BAO signal: systematic effects?**

Unbiased measurement Accuracy of distance scale measurement Scatter from 50 LBASICC runs: each one has volume 2.4 /h^3 Gpc^3 Angulo et al. 2008 redshift

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**Are BAO really a standard ruler?**

+/- 1% Correlation function is FT of P(k) BAO do not have constant wavelength or amplitude, so do not get a sharp feature Peak position is not equivalent to the sound horizon scale Need to model shape of correlation function on large scales Sanchez et al. 2008 Sound horizon Peak position Standard LCDM No Silk damping

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**Peak position is not sound horizon**

Sound horizon scale matter density Sanchez et al 2008

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**Systematics in the correlation function**

Different samples have same shape of correlation function: Real vs Redshift space No bias vs strong bias Sanchez et al. 2008 Correlation function less sensitive to effects causing gradients in P(k)

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**BAO measurements: update**

Cabre & Gaztanaga 2008 Analyse DR6 LRGs 1/h^3 Gpc^3 Also measurment of radial BAO Gaztanaga et al

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**Do BAO and SNe constraints agree?**

Modelling peak in correlation function gives consistent results with SNe. Sanchez et al. 2009 Equation of state parameter matter density

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**Ongoing/Future BAO measurements**

Spectroscopic: WiggleZ, FMOS, BOSS, HETDEX, LAMOST, Euclid (ESA), IDECs (NASA+ESA?) Photometric: Pan-STARRs, DES, LSST require ~ order magnitude more solid angle to be competitive with z-survey (Cai et al 2009) New surveys will ultimately probe on the order of 100 /h^3 Gpc^3

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**The future for modelling**

Simulate quintessence model w = w0 + w1(1-a) is not accurate model Jennings et al 2009 Equation of state parameter Expansion factor

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**Simulating quintessence DE**

Models have different expansion histories to LCDM Structure grows at different rates Models with appreciable DE at early times have different linear theory P(k) Jennings et al 2009 Dark energy density parameter

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**Baryon acoustic oscillations**

z=0 SUGRA Stage I : SUGRA linear growth factor Multiplicative factor f corrects the scatter of the measured power from the expected linear theory Invisible Universe 2009 Elise Jennings

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**Baryon acoustic oscillations**

z=0 SUGRA Stage I : SUGRA linear growth factor Stage II : SUGRA linear theory Elise Jennings

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**Baryon acoustic oscillations**

z=0 SUGRA Stage I : SUGRA linear growth factor Stage II : SUGRA linear theory Stage III: SUGRA best fit parameters 5% shift in second peak Elise Jennings

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**Baryon acoustic oscillations**

z=3 Elise Jennings

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**Baryon acoustic oscillations**

Z=0 z=0 AS Stage I : AS linear growth factor Elise Jennings

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**Baryon acoustic oscillations**

z=0 AS Stage I : AS linear growth factor Stage II : AS linear theory Shift in second peak using LCDM parameters Sound horizon at lss CDM rs = Mpc Stage I: AS rs = 137.8Mpc Elise Jennings

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**Baryon acoustic oscillations**

z=0 AS Stage I : AS linear growth factor Stage II : AS linear theory Stage III: AS best fit parameters <1% shift in second peak compared to CDM Sound horizon at lss CDM rs = 146.8Mpc Stage III: AS rs = 149.8Mpc Elise Jennings

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**Baryon acoustic oscillations**

z=3 Elise Jennings

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**The future for modelling**

Hard to distinguish LCDM and AS model from BAO Jennings et al 2009 Equation of state parameter Expansion factor

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Summary Starting a new age of BAO: beyond the approximate standard ruler BAO remove some of shape information in two-point correlation function Use realistic modelling to generate templates for BAO features to constrain parameters Current SNe and BAO results now consistent May be impossible to distinguish some DE models Need to refine simulations in two ways: Larger volumes able to resolve galactic haloes Simulate other DE scenarios

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