Cosmological Constraints from Baryonic Acoustic Oscillations Carlton Baugh

Cosmological Constraints from Baryonic Acoustic Oscillations Carlton Baugh Institute for Computational Cosmology Durham University Unity of the Universe Portsmouth 30 th June 2009

Outline: cosmology from BAO • BAO: the basics • BAO: in practice • Constraining dark energy: the next steps

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

The BAO signal RADIATION MATTER Meiksin, White & Peacock 1999 • 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 Divide matter spectrum by Featureless reference to Emphasize BAO signal

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

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

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

Detection of BAO Best fit Linear theory Convolved with Survey window function Cole et al. 2005 2 d. FGRS main galaxy sample

How well do we need to measure BAO? Dark energy equation of state • Hold other cosmological parameters fixed • dw ~ 7 ds (z=3) • dw ~ 4 ds (z=1) distance scale measurement Angulo et al. 2008

How well do we need to measure BAO? Dark energy equation of state • s/Da held fixed • dw ~ 2 ds (z=3, z=1) distance scale measurement Angulo et al. 2008

BAO data: recent snapshot • Percival et al 2007 • Joint analysis of 2 d. FGRS, SDSS main, SDSS LRG • For a flat universe and constant w, using WMAP s and SNLS data:

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. 2007

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

The evolution of BAO Dark matter Sample variance in 500/h Mpc box galaxies Springel et al. 2005

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

Combine with galaxy formation model H-alpha emitters z=1 Alvaro Orsi et al. 2009 H-band selection

Distortions to the BAO signal • Nonlinear growth of fluctuations Angulo et al. 2008

Distortions to the BAO signal • Nonlinear growth of fluctuations • Redshift space distortions Angulo et al. 2008

Distortions to the BAO signal Remove asymptotic bias: Scale dependent halo bias Angulo et al. 2008

Distortions to the BAO signal Scale dependent galaxy bias Angulo et al. 2008

Distortions to the BAO signal • Nonlinear growth of fluctuations • Redshift space distortions • Scale dependent halo and galaxy bias Angulo et al. 2008

Extracting the BAO signal Define reference spectrum from measurement Percival et al 2007 Angulo et al 2008

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

Accuracy of distance scale measurement Extracting the BAO signal: systematic effects? Unbiased measurement Scatter from 50 LBASICC runs: each one has volume 2. 4 /h^3 Gpc^3 Angulo et al. 2008 redshift

Are BAO really a standard ruler? +/- 1% Correlation function is FT of P(k) Peak position Standard LCDM No Silk damping Sound horizon 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 scale Peak position is not sound horizon matter density Sanchez et al 2008

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

BAO measurements: update • Cabre & Gaztanaga 2008 • Analyse DR 6 LRGs • 1/h^3 Gpc^3 • Also measurment of radial BAO Gaztanaga et al

Do BAO and SNe constraints agree? Equation of state parameter • Modelling peak in correlation function gives consistent results with SNe. • Sanchez et al. 2009 matter density

Ongoing/Future BAO measurements • Spectroscopic: Wiggle. Z, 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

The future for modelling Equation of state parameter • Simulate quintessence model • w = w 0 + w 1(1 -a) is not accurate model • Jennings et al 2009 Expansion factor

Dark energy density parameter 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

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

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

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

Baryon acoustic oscillations z=3 Elise Jennings

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

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 = 146. 28 Mpc Stage I: AS rs = 137. 8 Mpc Elise Jennings

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. 8 Mpc Stage III: AS rs = 149. 8 Mpc Elise Jennings

Baryon acoustic oscillations z=3 Elise Jennings

The future for modelling Equation of state parameter • Hard to distinguish LCDM and AS model from BAO • Jennings et al 2009 Expansion factor

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