Lyman-α forest as a precisioncosmology probe

Anze Slosar

IG matters,June 2014

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Introduction

I Lyman-α forest as a tracer of structure in the high-z universe

I Field revolutionized by BOSS

I Joint BOSS BAO constraintsI I will not talk about:

I Lyman-β forest power spectrum measurementsI PDF constraints

I This will be a very BOSS-centric talk

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Measuring Density fields

I Disclaimer: plot does notshow number densitiesand does not includephotometric experiments

I Lyman-α forest uniqueprobe ofthree-dimensionalstructure at redshiftsz = 2 − 3.5

I This is an importantepoch: last time Universewas truly de-Sitter

I Systematics verydifferent from galaxies astracers

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From baryons to fluxAbsorption done by neutral hydrogen in photo-ionizationequilibrium:

ΓnHI = α(T )npne (1)

nHI =α(T )ρ2

b

Γ 1 (2)

and so the absorbed flux fraction is given by

f = exp (−τ) ∼ exp(−A(1 + δb)1.7

)(3)

I We are observing a very non-linear transformation of theunderlying density field.

I On large scales, Lyman-α forest is simply a biasedtracer.

I On small scales, physics can be understood from firstprinciples.

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1D vs 3D

I Lyman-α forest is mapping the Universethrough a very weird window function

I Historically: few and far apart high SNRmeasurements

I Quasars can be assumed independent inthat limit: measure the 1D powerspectrum of flux fluctuations

I With SDSS12: resolution down, noise up,quasar number up (from few tens to15,000), but limited to 1D

I With SDSS3: noise further up, quasarnumber up (to 160,000): can finallymeasure correlations in three dimensions.

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1D vs 3D

Power spectrum of Lyα measures:

I small scales (1D, ∼ 0.1 Mpc/h): Effectsof warm dark matter, sterile neutrinos,etc.

I medium scales (1D, ∼ 1 Mpc/h):Inflation models, masses of lightneutrinos, etc.

I large scales (3D, > 10 Mpc/h): Baryonicacoustic oscillations (dark energy,curvature of the universe), measurementof the shape of matter power spectrum

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BOSS spectra

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1D power spectrum from BOSSI Work done by Saclay groupI Palanque-Delabrouille et al, arxiv:1306.5896I Selected ∼ 14, 000 quasars from ∼ 90, 000I Using two methods: the FFT and likelihood maximization

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1D power spectrum from BOSS

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3D sampling of the universe

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14k QSOs: ξ pushI Clear detection of

correlations with nosignificantcontamination

I The measuredcorrelation functionis distorted due tocontinuum fitting

I Analysis is harderthan galaxyanalysis:

I Redshift-spacedistortionsalways matter

I Redshift-evolution doesmatter

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140k QSOs in DR11: BAO

from de Lubac et al, 201412 / 26

What is BAO?

BAO in Cosmic MicrowaveBackground

BAO in CMASS galaxies

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BAO is a statical ruler

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BAO is a statical ruler

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Quasar - forest cross-correlation inBOSS

I Detection of the BAO in the cross-correlation between QSO and forest byAndreu Font & co.

I Ability for BOSS to do this has not been predicted, but constraining powernearly as powerful as with flux auto-correlation

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Houston, we have a problem

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World BAO data

0.10 1.000.2 0.5 2.0z

10

20

D(z

)/r d√z

DA(z)/rd√z

DV (z)/rd√z

DH(z)/rd√z

6dFGS

MGS

SDSS− II

WiggleZ

LOWZ

CMASS

Lyα auto

Lyα cross

I Collection of world BAO dataI Lines are Planck best fit predictions

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ΛCDM BOSS BAO

0.5 0.6 0.7 0.8 0.9 1.0

h

0.0

0.2

0.4

0.6

0.8

1.0Ωm

Galaxy BAOLyman-α BAOCombined BAOPlanck PLA

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World BAO data

0.0 0.1 0.2 0.3 0.4 0.5Ωm

0.0

0.2

0.4

0.6

0.8

1.0

1.2Ω

ΛCombined BAOCombined BAO+Planck DA

I BAO data alone detect the dark energy at > 3σ20 / 26

World BAO data

0.0 0.2 0.4 0.6 0.8 1.0 1.2ΩΛ

0

2

4

6

8

10

12

14p

rob.

Combined BAOGalaxy BAO+Planck DA

Lyman-α BAO+Planck DA

Combined BAO+Planck DA

I BAO data alone detect the dark energy at > 3σ

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Inverse distance ladder

I Inverse distance ladder transfer H0 measurement from redshiftof observation to z = 0 using Supernovae Type Ia

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Inverse distance ladder

55 60 65 70 75 80 85 90

H0[kms−1Mpc−1]

ow0wa-CDM GBAO+SN+rd

PolyCDM GBAO+SN + rdInverseDistance Ladder

ΛCDM Planck (full)

ΛCDM WMAP (full)CMB+ΛCDM

Riess++

Freedmann++

EfstathiouDistance Ladder

I BOSS prefers low-h Universe: H = 68.1 ± 1.2

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Neutrino mass from geometry:

0.0 0.2 0.4 0.6 0.8 1.0Σmν

0

1

2

3

4

5

6

7

8p

rob.

BAO+PlanckPLA Planck+BAO (w Alens)PLA Planck+BAO (w/o Alens)

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“the tension”

0.10 1.000.2 0.5 2.0 5.0log(1 + z)

10.0

20

50

D(z

)/r d√z

DM(z)/rd√z

DV (z)/rd√z

DH(z)/rd√z

6dFGS

LOWZ

CMASS

Lyman− α auto

Lyman− α cross

CMB DM/rD

I Tension just about∼ 2.5σ

I Very hard to solve it withe.g. early dark energy

I Fine-tune solutionspossible, but contrived

I Increasing Neff helps withLyman-α , increasesz = 0 Hubble parameter,lowers low-z σ8,decreases tension withBICEP.

I The price you pay isincompatibility withgalaxy BAO and ns ∼ 1.

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Conclusions

I Life is good

I Lyman-α BAO exhibits a small tension with ΛCDM cosmologyI The future is bright, most promise in small scale P1D:

I Neutrino massI Neff

I running of spectral index

I More data on horizon: the 400 public hi resolution QSOspectra, eBOSS, DESI

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