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Baryonic acoustic

oscillations:

Past, Present

and Future

Collaborators:Steve Rawlings (Oxford), Chris Blake (Swinbourne) M. Banerji, Sarah Bridle, E. Cypriano, O. Lahav (UCL)

A. Amara (Saclay) P. Capak, J Rhodes (Caltech/JPL)

(DES/DUNE/SKA working groups)(DES/DUNE/SKA working groups)

F. B. Abdalla

5/29/20075/29/2007 Filipe B. Filipe B. AbdallaAbdalla (UCL)(UCL)

Cosmology: Concordance ModelCosmology: Concordance Model

Outstanding questions:

• initial conditions (inflation?)

• nature of the dark matter

• nature of the dark energy

• value of the neutrino mass

Heavy elements 0.03%

Neutrinos 0.3%

Stars 0.5%

H + He gas 4%

Dark matter 20%

Dark Energy 75%

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Acoustic oscillations:Acoustic oscillations:

•• There are fluctuations at all scales but There are fluctuations at all scales but

there is a preferred scale of around 1 deg.there is a preferred scale of around 1 deg.

Sound waves:Sound waves:

Before recombination:

• Universe is ionized.

• Photons provide enormous pressure and restoring force.

• Perturbations oscillate as acoustic waves.

After recombination:

• Universe is neutral.

• Photons can travel freely past the baryons.

• Phase of oscillation at trec affects

late-time amplitude.

Eisenstein

Wayne Hu

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Sound WavesSound Waves

• At recombination the fundamental wave is frozen in a phase where gravity

enhances the gravitational pull, but only ordinary matter undergoes sonic

compressions.

• The dark matter pull in baryons and photons by gravitational attraction.

• At recombination gravity and sonic motion work together to raise the radiation

temperature in the troughs (blue) and lower the temperature at the peaks (red).

Eisenstein

BAO in LSSBAO in LSS

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• comoving distance

• standard candles

• standard rulers

• volume factor

• growth of structure depends on H(z) probed with

power spectrum

TheThe Expansion History of the UniverseExpansion History of the Universe

Looking back in time in the Universe

FLAT GEOMETRYCREDIT: WMAP & SDSS websites

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Looking back in time in the Universe

CLOSED GEOMETRY

Looking back in time in the Universe

CREDIT: WMAP & SDSS websites

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SDSS BAO: Model ComparisonSDSS BAO: Model Comparison

Equality scale depends

on (Ωmh2)-1.

Acoustic scale depends

on (Ωmh2)-0.25.

Ωmh2 = 0.12

Ωmh2 = 0.13

Ωmh2 = 0.14

CDM with baryons is a good fit: χ2 = 16.1 with 17 dof.

Pure CDM rejected at ∆χ2 = 11.7

Ωbh2 = 0.00

Fixed

Ωbh2=0.024

ns=0.98, flatEisenstein et al. 05

WMAP & SDSS WMAP & SDSS fourrierfourrier spacespace

Percival et al. 06

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BAO systematic effects:BAO systematic effects:

Systematic effects:Systematic effects:

galaxy biasgalaxy bias

Springel et al 05Cole, Sanchez & Wilkins 06

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BAO systematic effects:BAO systematic effects:

Their power spectra mock data is availableAnd it is possible to retrieve the wiggles without Shift by fitting splines to the broad band shape of P(k) (Percival)

Galaxy spectrum at 3 different redshifts, overlaid on griz and IR bandpasses

• Photometric redshifts (photo-z’s) are determined from the fluxes of galaxies through a set of filters• May be thought of as low-

resolution spectroscopy

• Photo-z signal comes primarily from strong galaxy spectral features, like the 4000 Å break, as they redshiftthrough the filter bandpasses

• All key projects depend crucially on photo-z’s

• Photo-z calibrations will be • optimized using both simulated

catalogs and images.

Photometric Photometric RedshiftsRedshifts

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Training Set Training Set

MethodsMethods

•• Determine Determine

functional relationfunctional relation

zphot = zphot (m,c)

•• ExamplesExamples

Neural Network

(Firth, Lahav & Somerville 2003;

Collister & Lahav 2004)

Polynomial

Nearest

Neighbors

(Cunha et al.

in prep. 2005)

Template Fitting Template Fitting

methodsmethods

•• Use a set of standard Use a set of standard SED’sSED’s --

templatetemplatess (CWW80, etc.)(CWW80, etc.)

•• Calculate fluxes in filters of Calculate fluxes in filters of

redshiftedredshifted templates.templates.

•• Match object’s fluxes (Match object’s fluxes (χχ22

minimization)minimization)

•• Outputs Outputs typetype and and redshiftredshift

•• Bayesian PhotoBayesian Photo--zzHyper-z (Bolzonella et al. 2000)

BPZ (Benitez 2000)

Polynomial

(Connolly et al. 1995)

Nearest Neighbors

(Csabai et al. 2003)

ANNzANNz -- Artificial Neural NetworkArtificial Neural Network

Output:

redshiftInput:

magnitudes

Collister & Lahav 2004http://www.star.ucl.ac.uk/~lahav/annz.html

z = f(m,w)

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*Training on ~13,000 2SLAQ*Training on ~13,000 2SLAQ

*Generating with *Generating with ANNzANNz

PhotoPhoto--z for ~1,000,000 z for ~1,000,000 LRGsLRGs

MegaZMegaZ--LRGLRG

σz = 0.046

Collister, Lahav,

Blake et al.,

astro-ph/0607630

(DR4)

Abdalla et al.

in prep (DR5)

Baryon oscillations

Blake, Collister, Bridle & Lahav; astro-ph/0605303Padmanabhan et al (parallel work)

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BAO with photoBAO with photo--z.z.

•• Can clearly see the Can clearly see the effect of the smoothing effect of the smoothing due to the photodue to the photo--z in z in P(kP(k) convolution in real ) convolution in real space is a multiplication space is a multiplication in Fourier space.in Fourier space.

•• Line of sight Line of sight vsvs plane of plane of the sky effects. Here the sky effects. Here angle averaged.angle averaged.

•• Photometric Photometric redshiftsredshiftsare very accurate for are very accurate for galaxy clusters. galaxy clusters. δδzz =0.025=0.025

•• Number density / Number density / volume are not enough volume are not enough to produce wiggle to produce wiggle measurements but…measurements but…

Seo & Eisenstein 05Huetsi 07

BAO in DES: Galaxy Angular Power Spectrum

Probe substantially

larger volume and

redshift range than

SDSS

Systematics:

photo-z’s,

photometric errors

Wiggles due

to BAO

Blake & BridleFosalba & Gaztanaga

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Many power spectra:Many power spectra:

Cleaned photometric Cleaned photometric redshiftsredshifts::

Motivation:

Remove systematic

effects associated

to catastrophic outliers

Calibrating these

photo-z requires

around a million spectra.

Method:

Abdalla, Amara, Capak,Cypriano, Lahav, Rhodes 07

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Less modes with photoLess modes with photo--z:z:

Blake & Bridle 05

The SKA:The SKA:•• An extremely powerful survey An extremely powerful survey

telescope with the capability telescope with the capability

to follow up individual objects to follow up individual objects

with high angular and time with high angular and time

resolutionresolution

•• ~ 1 km2 collecting area ~ 1 km2 collecting area

–– limited gains achievable by limited gains achievable by

reducing receiver noise reducing receiver noise

–– need more microwave photonsneed more microwave photons

•• Frequency range 0.1 Frequency range 0.1 –– 25 GHz25 GHz

•• Angular resolution: 0.1 Angular resolution: 0.1 arcsecarcsec @ 1.4 GHz@ 1.4 GHz

•• FOV: ~ 50+ deg^2FOV: ~ 50+ deg^2

•• 1515--country international collaborationcountry international collaboration

•• Technology selection in 2008; initial operations 2015; full Technology selection in 2008; initial operations 2015; full operations 2020. Pathfinder ~ 2015operations 2020. Pathfinder ~ 2015--2017.2017.

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What will the SKA see?What will the SKA see?

Normal/Starburst galaxiesNormal/Starburst galaxies

SKA results on w:SKA results on w:

•• Pathfinder equivalent Pathfinder equivalent to WFMOS ~ below 5%to WFMOS ~ below 5%

•• Full SKA gets error to Full SKA gets error to ~.7% with wiggles ~.7% with wiggles +CMB+CMB

•• Number of galaxies Number of galaxies probed: 10probed: 109 9 from z=0 from z=0 to z=2 (to z=2 (AbdallaAbdalla & & Rawlings 05)Rawlings 05)

•• Probe which is Probe which is independent of Planck independent of Planck priors.priors.

Abdalla, Blake & Rawlings 07 in prep.

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Conclusions:Conclusions:•• BAO are imprinted in the galaxy population: this yields a new BAO are imprinted in the galaxy population: this yields a new

probe, but beware of galaxy clustering as a source of probe, but beware of galaxy clustering as a source of systematic effects. Specially helps breaking other systematic effects. Specially helps breaking other degeneraciesdegeneracies in cosmological parameters.in cosmological parameters.

•• Many efforts to measure BAO using spectra, clusters, Many efforts to measure BAO using spectra, clusters, photometric photometric redshiftsredshifts, etc… most results range from 2, etc… most results range from 2--3 3 sigma.sigma.

•• The next steps in this directions will be produced by The next steps in this directions will be produced by photometric surveys with photophotometric surveys with photo--zz

•• The photometric The photometric redshiftsredshifts have to be well calibrated and have to be well calibrated and unbiased: this can be done with a small spectroscopic sample.unbiased: this can be done with a small spectroscopic sample.

•• PhotoPhoto--z smear out information: The area needed for this is z smear out information: The area needed for this is ~10 times larger than in we had spectra for realistic photo~10 times larger than in we had spectra for realistic photo--z z errorserrors

•• Following this, the way forward is to make all sky Following this, the way forward is to make all sky spectroscopic surveys. This can be done in the radio and will spectroscopic surveys. This can be done in the radio and will provide constraints of w~0.7% alone. Systematic effects must provide constraints of w~0.7% alone. Systematic effects must be below that level!!!be below that level!!!