Dark Energy Studies: Galaxy Surveys Ramon Miquel ICREA / IFAE - - PowerPoint PPT Presentation

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APPEC Town Hall Meeting, Paris, April 7, 2016

Dark Energy Studies: Galaxy Surveys

Ramon Miquel ICREA / IFAE Barcelona

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Outline

• Introduction
• Survey of current and future galaxy surveys
• Examples: BOSS, DES, DESI, LSST, Euclid
• Complementarity, also with CMB
• Neutrino mass
• European perspective: SWOT analysis
• Conclusions

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Dark Energy Studies

• What is causing the acceleration of the expansion of the universe?
• Einstein’s cosmological constant Λ?
• Some new dynamical field (“quintessence,” Higgs-like)? “Dark Energy”
• Modifications to General Relativity?
• Dark energy effects can be studied in two main cosmological observables:
• The history of the expansion rate of the universe: supernovae, weak lensing,

baryon acoustic oscillations (BAO), cluster counting, etc.

• The history of the rate of the growth of structure in the universe: weak lensing,

large-scale structure, cluster counting, redshift-space distortions, etc.

• For all probes other than SNe, large galaxy surveys are needed:
• Spectroscopic: 3D (redshift), medium depth, low density, selection effects
• Photometric: “2.5D” (photo-z), deeper, higher density, no selection effects

}

Instrument Telescope Bands

• No. Gal.
• Sq. Deg.

z max Leader KiDS VST 2.6 ugri 90M 1500 1.5 ESO VHS Vista 4 YJHKs 400M 20000 1.2 ESO Viking Vista 4 ZYJHK

IR complement to KiDS

1500 1.5 ESO PS1 Hawai’i 1.8 grizy 1B 30000 1.0 USA DES Blanco 4 grizy 300M 5000 1.5 USA SuMIRe HSC Subaru 8.2 grizy 100M 1400 1.5 Japan PAU WHT 4 40 narrow bands 2M 100-200 1.2 Spain J-PAS OAJ 2.5 54 narrow bands 14M LRG 8000 1.2 Spain LSST LSST 8.4 ugrizy 4B 20000 3.0 USA Euclid Space 1.2 R+I+Z YJH 1.5B 15000 2.0 ESA

Photometric Galaxy Surveys

Now

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Spectroscopic Galaxy Surveys

Instrument Telescope

• No. Gal.
• Sq. Deg.

z max Leader SDSS APO 2.5 85K LRGs 7600 0.6 USA Wiggle-Z AAT 3.9 239K 1000 0.7 Australia BOSS APO 2.5 1.4M LRGs + QSOs 10000 0.7 USA eBOSS APO 2.5 600K 7500 1.0 USA / CH HETDEX HET 9.2 1M 420 3.0 USA DESI Mayall 4 30M + QSOs 14000 3.0 USA SuMIRe PFS Subaru 8.2 4M 1400 2.4 Japan 4MOST VISTA 4.1 ?? 15000 1.5 ESO Euclid Space 1.2 50M 15000 2.0 ESA

Now

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Status of BOSS

• BOSS finished data taking in July 2014
• DR12 publicly available since January 2015, containing all

data.

Aubourg et al., PRD 92 (2015) 123516 DR11 9400 deg2

Status of DES

• DES has already operated for 3 out of 5 seasons.
• Most results only available for “Science Verification” period.

7 Chang et al., PRL 115 (2015) 05301

(Dark) matter mass map Science Verification: ~150 deg2 at full depth ~10 M galaxies ~3% of full survey

What is DESI?

• Stage-IV BAO and RSD survey,

built upon BOSS

• Massively parallel fiber-fed

spectrometer at the 4-meter Mayall telescope

• Automated fiber system:

Nfiber = 5000

• Sky coverage: 14,000 sq. deg.
• Number of galaxy redshifts: 30 M
• CD-3 review in May 2016
• Commissioning in 2019

New spectrographs New 3 deg ∅ FoV corrector 5000 fiber actuators

100% of dark time for 5 years

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What is DESI?

4 million LRGs 24 million ELGs 0.6 million Ly-α QSOs + 1.6 million QSOs

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SDSS ~2h-3Gpc3 BOSS ~6h-3Gpc3 DESI 50h-3Gpc3

What is DESI?

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DESI: Very Precise Distance Measurements

Fractional Distance Error

DESI

What is DESI?

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DESI Science Reach

1 2 3 4 5 6 7

rms error improvement over Planck + BOSS BAO

wp w’ ωk Σ mν ns αs N ν,l

σ = 0.023 σ = 0.014 σ = 0.28 σ = 0.13 σ = 5.2 × 10

− 4

σ = 3.6 × 10

− 4

σ = 0.09 σ = 0.017 σ = 3.8 × 10

− 3

σ = 2.2 × 10

− 3

σ = 4 × 10

− 3

σ = 2 × 10

− 3

σ = 0.084 σ = 0.063

D E S I g a l a x y a n d L y a F B A O + g a l a x y b r

• a

d b a n d k < . 2 h / M p c + L y a F b r

• a

d b a n d

Now

What is LSST?

FASTER (2×15s exp.), WIDER (20k deg2), DEEPER (i ~ 26.8) DES: 90s exp. 5k deg2 i ~ 23.8

– 8.4 m diameter mirror – 9.6 deg2 field of view – 825 visits per pointing – 10 million alerts per night – 40 billion objects – 500 PB of images – 10 year survey – Commissioning starts in 2021 – Weak lensing with 4 billion galaxies

Ivecić et al. 2014, arXiv:0805.2366v4

The LSST Camera

Camera weighs ~3 tons

LSST Construction Started on 2015-04-14

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What is Euclid?

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Launch in 2020

Euclid: Imaging + Spectroscopy

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30 gal / arcmin2

Euclid Science Reach

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Now: Betoule et al. 2014

Euclid Reach in DE Equation of State

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geometric

DETF Figure of Merit: inverse area of ellipse Stage III project 68% CL

Planck prior assumed geometric + growth

DES forecast

w = pDE/ρDE, w(z) =w0+wa(1–a)

Now: Betoule et al. 2014

Euclid Reach in DE Equation of State

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geometric

DETF Figure of Merit: inverse area of ellipse Stage III project 68% CL

Planck prior assumed geometric + growth

DES forecast

w = pDE/ρDE, w(z) =w0+wa(1–a)

Now: Betoule et al. 2014

Euclid Reach in DE Equation of State

18 Euclid forecast

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Cross-Correlations: Spectroscopy with Imaging

Shapes: images, background RCSLenS CFHTLenS Lenses: spectra, foreground BOSS WiggleZ

Blake et al. 2016, MNRAS 456, 2806

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Cross-Correlations: Spectroscopy with Imaging

Blake et al. 2016, MNRAS 456, 2806

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Cross-Correlations: Spectroscopy with Imaging

Blake et al. 2016, MNRAS 456, 2806

Planck: 0.82 ± 0.01

Galaxy lensing × CMB lensing (amplitude of matter fluctuations)

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Cross-Correlations: Galaxies with CMB

Hand et al. 2015, PRD 91, 062001 (CFHT Stripe 82 × ACT)

Galaxy density × CMB lensing (amplitude of matter fluctuations)

Giannantonio et al. 2016, MNRAS 456, 3213 (DES × SPT / Planck)

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Neutrino Mass

All next generation surveys have the sensitivity to reach a detection

Ex: DESI (+ Planck) forecast a sensitivity ~ 0.017 eV

< 0.23 eV @ 95% CL

Planck 2015, arXiv:1502.01597

< 0.15 eV @ 95% CL

Palanque-Delabrouille et al. 2015, JCAP 1511, 011

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European Perspective

• Photometric surveys:
• Current ESO surveys lie somewhere between SDSS and DES
• Nothing planned for the near future
• Very significant French participation in LSST
• Spectroscopic surveys:
• No clear proposal for cosmology-oriented spectroscopic surveys
• 4MOST and WEAVE are mostly designed for follow-up of Gaia
• In any case, not quite competitive with DESI
• But, of course, there’s Euclid!

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Strengths

• Euclid will dominate DE science from space in the next
• decade. Clear European leadership.
• World-leading in weak lensing
• Very competitive in BAO (although DESI may be stronger)
• Excellent SN program (currently not guaranteed)
• Broad European participation in the leading ground-based

DE surveys

• BOSS, DES, eBOSS, DESI, LSST
• Negotiations still on-going for DESI and LSST

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Weaknesses

• No European leadership on ground-based DE projects
• KiDS is the only major current European-led project: similar to DES

but smaller

• No guaranteed time-domain science in Euclid. No SNe
• Euclid relies on ground-based (and non-EU-led) surveys for

photometric redshifts + systematic error control (see later).

• Data exchange between Euclid and LSST should be encouraged.

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Opportunities

• Large US-led projects (LSST, DESI) will allow fruitful

European participation at a fraction of the investment that would have been needed had they been led from Europe (much like LHC for the US)

• PAU and J-PAS are low-cost European-led new initiatives

that combine photometric and spectroscopic features

• They can provide excellent help in controlling the most dangerous

systematic errors limiting Euclid weak lensing science reach: intrinsic alignments, photo-z calibration

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Threats

• Funding for DE science is split between HEP (APPEC) and

astronomy (ASTRONET) agencies

• In times of decreasing budgets, agencies focus on their core

competencies, and DE science may fall through the cracks

• There might be difficulties in securing funding for US-led

projects

• ESO does not have a strong suite of world-leading projects in DE

science, either photometric or spectroscopic, either active or planned

• However, astronomy funding agencies in ESO member countries

are (rightly) expected to prioritize ESO projects (just like HEP funding agencies in CERN member states prioritize CERN projects)

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Conclusions (I)

• Dark Energy is a profound mystery that deserves the high attention

is receiving.

• Imaging / Spectroscopy, Ground / Space are complementary and

synergistic:

• Imaging: efficient; deep; 2.5D for many methods; allows weak

lensing.

• Spectroscopy: 3D info for BAO, RSD
• Space: exquisite stable PSF for lensing; access to near-infrared
• Ground: larger telescopes allow fast, wide, deep surveys
• Combination of data from different surveys can be very

powerful; also the combination with CMB. This needs to be facilitated and encouraged.

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Conclusions (II)

• The US dominates dark energy studies with galaxy surveys from the ground,

both photometric and spectroscopic:

• Past: SDSS (stage II)
• Present: (e)BOSS, DES (stage III) (but KiDS @ ESO and HSC/SuMIRe

in Japan can be competitive)

• Future: DESI, LSST (stage IV)
• There is good European participation in these US-led projects.
• DESI, LSST will dominate dark energy studies from the ground from ~2020.
• Europe will lead from space with Euclid from ~2020.
• Europe should support Euclid in the strongest possible terms. Euclid is

mostly funded by ESA and the national space agencies, outside of APPEC.

• LSST, DESI deserve the highest priority from the funding agencies in
• APPEC. LSST is also discussed in ASTRONET.