Dark Energy Studies: Galaxy Surveys Ramon Miquel ICREA / IFAE Barcelona APPEC Town Hall Meeting, Paris, April 7, 2016 1
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 2
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 3
Photometric Galaxy Surveys 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 IR complement to Viking Vista 4 ZYJHK 1500 1.5 ESO KiDS PS1 Hawai’i 1.8 grizy 1B 30000 1.0 USA Now DES Blanco 4 grizy 300M 5000 1.5 USA SuMIRe HSC Subaru 8.2 grizy 100M 1400 1.5 Japan 40 narrow PAU WHT 4 2M 100-200 1.2 Spain bands 54 narrow J-PAS OAJ 2.5 14M LRG 8000 1.2 Spain bands LSST LSST 8.4 ugrizy 4B 20000 3.0 USA Euclid Space 1.2 R+I+Z YJH 1.5B 15000 2.0 ESA
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 1.4M LRGs + BOSS APO 2.5 10000 0.7 USA QSOs Now 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 5
Status of BOSS • BOSS finished data taking in July 2014 • DR12 publicly available since January 2015, containing all data. 9400 deg 2 DR11 Aubourg et al., PRD 92 (2015) 123516 6
Status of DES • DES has already operated for 3 out of 5 seasons. • Most results only available for “Science Verification” period. (Dark) matter mass map Science Verification: ~150 deg 2 at full depth ~10 M galaxies ~3% of full survey 7 Chang et al., PRL 115 (2015) 05301
What is DESI? 5000 fiber actuators New 3 deg ∅ FoV corrector • Stage-IV BAO and RSD survey, built upon BOSS • Massively parallel fiber-fed spectrometer at the 4-meter Mayall telescope • Automated fiber system: N fiber = 5000 Sky coverage: 14,000 sq. deg. • Number of galaxy redshifts: 30 M • CD-3 review in May 2016 • New spectrographs Commissioning in 2019 • 100% of dark time for 5 years 8
What is DESI? SDSS ~2h -3 Gpc 3 BOSS ~6h -3 Gpc 3 DESI 50h -3 Gpc 3 0.6 million Ly- α QSOs + 1.6 million QSOs 24 million ELGs 4 million LRGs 9
DESI: Very Precise Distance Measurements What is DESI? Fractional Distance Error DESI 10
Now σ = 0.023 w p σ = 0.014 σ = 0.28 w’ DESI Science Reach σ = 0.13 What is DESI? σ = 5.2 × 10 − 4 ω k σ = 3.6 × 10 − 4 σ = 0.09 Σ m ν σ = 0.017 σ = 3.8 × 10 − 3 n s + + D σ = 2.2 × 10 − 3 L g E y a S a l I a F g x b y a l r a b o x a r σ = 4 × 10 − 3 y o d a b a α s d n a b σ = 2 × 10 d n − 3 a d L n y d a F k B < A σ = 0.084 O 0 N ν,l . 2 h σ = 0.063 / M p c 11 1 2 3 4 5 6 7 rms error improvement over Planck + BOSS BAO
What is LSST? FASTER (2 × 15s exp.), WIDER (20k deg 2 ), DEEPER (i ~ 26.8) DES: 90s exp. 5k deg 2 i ~ 23.8 – 8.4 m diameter mirror – 9.6 deg 2 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 Iveci ć et al. 2014, arXiv:0805.2366v4
The LSST Camera Camera weighs ~3 tons
LSST Construction Started on 2015-04-14 14
What is Euclid? Launch in 2020 15
Euclid: Imaging + Spectroscopy 30 gal / arcmin 2 16
Euclid Science Reach 17
Euclid Reach in DE Equation of State Now: Betoule et al. 2014 18
Euclid Reach in DE Equation of State w = p DE / ρ DE , w ( z ) =w 0 +w a (1 –a ) DES forecast DETF Figure of Now: Betoule et al. 2014 Merit: inverse area of ellipse 68% CL geometric + growth Stage III project geometric Planck prior assumed 18
Euclid Reach in DE Equation of State w = p DE / ρ DE , w ( z ) =w 0 +w a (1 –a ) DES forecast DETF Figure of Now: Betoule et al. 2014 Merit: inverse area of ellipse 68% CL geometric + growth Euclid forecast Stage III project geometric Planck prior assumed 18
Cross-Correlations: Spectroscopy with Imaging Shapes: images, background RCSLenS CFHTLenS Lenses: spectra, foreground BOSS WiggleZ Blake et al. 2016, MNRAS 456, 2806 19
Cross-Correlations: Spectroscopy with Imaging Blake et al. 2016, MNRAS 456, 2806 20
Cross-Correlations: Spectroscopy with Imaging Planck: 0.82 ± 0.01 Blake et al. 2016, MNRAS 456, 2806 21
Cross-Correlations: Galaxies with CMB Galaxy density × CMB lensing Galaxy lensing × CMB lensing (amplitude of matter (amplitude of matter fluctuations) fluctuations) Hand et al. 2015, PRD 91, 062001 (CFHT Stripe 82 × ACT) Giannantonio et al. 2016, MNRAS 456, 3213 (DES × SPT / Planck) 22
Neutrino Mass < 0.15 eV @ 95% CL < 0.23 eV @ 95% CL Planck 2015, arXiv:1502.01597 Palanque-Delabrouille et al. 2015, JCAP 1511, 011 All next generation surveys have the sensitivity to reach a detection Ex: DESI (+ Planck) forecast a sensitivity ~ 0.017 eV 23
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! 24
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 25
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. 26
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 27
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) 28
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. 29
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