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Cosmology with Lyα forests from BOSS
James Rich
DPhP-IRFUCEA-Saclay
91191 Gif-sur-Yvette
CosmoBack, May , 2018
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Outline
The Lyα forest
BOSS“Baryon Oscillation Spectroscopy Survey”
Baryon Acoustic Oscillations in the forestCosmological parameters from BAO
Reconstructing the linear power spectrumConstraints on neutrino massesWarm dark matterFuzzy dark matter
Future projects
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Quasar = Black hole accreting hot gas
Spectrum: power-law + emission lines
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Quasar = Black hole accreting hot gas
Absorption by atomic hydrogen (HI) blueward of Lyα emission
Absorption at λobserved depends on nHI at z + 1 = λobs/1215.
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Need to model the smoothed forest spectrum
1 + δ(λ, ~θ) =
observed flux
expected flux
Fluctuations of nHI and of radial-velocity gradiant
⇒ Fluctuations of δ(λ, ~θ)
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Correlate forests to find ξ(r⊥, r‖)
ξ(r⊥, r‖) =
∑wiwjδiδj∑wiwj
.
Sums over pixel pairs (i , j)
separated by (r⊥, r‖)
Weight, wi , is chosen to minimize
variance of ξ.
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BOSS results: Bautista et al. (2017)
BAO peak at r = rd (sound horizon)
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Measured quantities (∆θ,∆z)
∆θ =r⊥
DM(z)∆z =
r‖DH(z)
⇒ BAO peak position determines
rd/DM(z) (transverse)
rd/(c/H(z)) (radial)
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BOSS: Baryon-Oscillation Spectroscopy Survey
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BOSS Spectrograph
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BOSS Spectrograph,CCD
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2 BOSS surveys (104deg 2 5 years)
6× 105 Large Red Galaxies (LRG)∼ 500 fibers per plate
(candidates from SDSS-I photometry)〈z〉 ∼ 0.6, n ∼ 10−4Mpc−3
BAO results: arXiv:1607.03155
1.6× 105 quasars with Lyα absorption∼ 280 fibers per plate
(candidates from SDSS-I photometry)〈z〉 ∼ 2.4BAO results: arXiv:1702.00176; 1708.02225
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Outline
The Lyα forest
BOSS“Baryon Oscillation Spectroscopy Survey”
Baryon Acoustic Oscillations in the forestCosmological parameters from BAO
Reconstructing the linear power spectrumConstraints on neutrino massesWarm dark matterFuzzy dark matter
Future projects
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Correlate forests
Bautista et al. (2017)Nearly radial direction:
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Correlate quasars and forestsdu Mas des Bourboux et al. (2017)
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Constraints on (DM/rd ,DH/rd ) at z = 2.4
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Summary of BAO measurements of D/rd
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BAO H(z) ⇒ deceleration→acceleration
ΛCDM prediction
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BAO (DM(z)/rd ,DH(z)/rd ) ⇒ (ΩΛ,ΩM , rdH0)
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Top-down: the BAO and SNIa Hubble diagram
Aubourg et al. arXiv:1411.1074
Calibrate SNIa luminosityby requiringDM(z = 0.57) from SNIaagree withDM(z = 0.57) from BAO
⇒ H0 = 67.3± 1.1
Distance ladder:H0 = 73.24± 1.74,arXiv:1604.01424
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Outline
The Lyα forest
BOSS“Baryon Oscillation Spectroscopy Survey”
Baryon Acoustic Oscillations in the forestCosmological parameters from BAO
Reconstructing the linear power spectrumConstraints on neutrino massesWarm dark matterFuzzy dark matter
Future projects
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Lyα flux transmission power spectrum
PF (~k) = Plin(k)b2F (1 + βµ2
~k)FNL(~k)
Bias parameters (bf , β).
FNL(~k) describes “non-linear” effects.
Galaxy power spectrum depends on unknown astrophysics of galaxyand star formation.
Lyα power spectrum depends on complicated but mostly understoodhydrodynamics of the inter-galactic medium.
⇒Use simulations of IGM to find (bF , β,FNL(~k)) to derive Plin(k)
from measured PF (~k)
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The Lyα forest: 1A ∼ 1Mpc
Low-resolution (BOSS)
High-resolution spectrum (Keck).Simulations must resolveJeans-length of IGM (∼ 100kpc).
Complications from non-HIabsorbers
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Predicted PF 3d (~k)/PL(k) (Arinyo et al.,2016)
0.01
0.1
0.1 1 10
PF(k
)/P
L(k
)
k [h/Mpc]
color: D1black: D1, q2 = 0
z = 2.2Radial direction
At small kPradial Ptransverse
(because b 1)
Transverse direction
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Predicted PF 3d (~k)/PL(k) (Arinyo et al.,2016)
0.01
0.1
0.1 1 10
PF(k
)/P
L(k
)
k [h/Mpc]
color: D1black: D1, q2 = 0
z = 2.2
Radial direction
At large kPradial suppressed(thermal broadening,chaotic velocityfield)
Transverse direction
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Radial Power: BOSS, VLT, Keck
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Deduced PL(k) (Palanque-Delabrouille et al
1410.7244)
Normalization of powerspectrum ∆2
Predicted by Planck ΛCDMin agreement withObserved in Lyαforest
⇒No room for extra freestreaming effects ofneutrinos
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Suppression of power by massive neutrinos.
Villaescusa et al.arXiv:1708.01154
Lyα P1d(k‖)0.2 < k‖ < 4
Pgalaxy (k)0.01 < k < 1
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Limits on∑
mν from Lyα -CMB comparison
Seljac, Slosar & McDonald (2006)∑
mν < 0.17 eVSDSSI + WMAP-3yr
Palanque-Delabrouille et al. (2015)∑
mν < 0.15 eVBOSS+Planck 1yr
Yeche et al. (2017)∑
mν < 0.14 eVBOSS+VLT+Planck 2015
All assume ns not running.DESI limit goal: σ(
∑mν) = 0.02eV∑
mν = 0.06 (0.11) for normal (inverted) mass ordering
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Warm or Fuzzy DM cuts off the power spectrum
WDM: free-streaming
kc ∼ 6 Mpc−1(mwdm
keV
)1.1FDM: deBroglie wavelength
kc ∼ 5 Mpc−1( mfdm
10−22eV
)0.46Observed large-k power consistent with expected thermal effectsBOSS,VLT,Keck Lyαpower⇒ mwdm >∼ 5keV [arXiv:1706.03118, 1702.03314]⇒ mfdm >∼ 3× 10−21eV [arXiv:1703.09126]
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Future: Dark Energy Spectroscopy Survey (DESI)
. BOSS H(z)
DESI H(z):arXiv:1611.000362.5M Sloan Telescope→4M Mayall1000fibers → 5000 fibers
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WEAVE
DESI: H(z) precision
WEAVE: precision withimproved quasar selectionusing J-PAS narrow-bandphotometry
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Lyα cosmology summary
Large CCD arrays and fiber-optic-fed
spectrometers have allowed (will allow)
BOSS→eBOSS→DESI to
Constrain parameters of homogeneous
cosmology with a well-understood standard
ruler from BAO
Study the small-scale power spectrum to place
constaints on massive neutrinos, warm dark
matter, and fuzzy dark matter.
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