1. Future observational prospects for dark energy Roberto Trotta Oxford Astrophysics & Royal Astronomical Society

2. R. Trotta - rxt@astro.ox.ac.uk Investigating dark energy The equation of state parameter w(z) = p/  – w = -1 – w = const  -1 – w(z) – or perhaps another theory of gravity Theoretical explanations must be guided by observational constraints: w eff ~ -1 § 0.2 for z < 1 TODAY Seljak et al 2005 Jarvis et a 2005

3. R. Trotta - rxt@astro.ox.ac.uk Observational techniques Weak gravitational lensing Baryonic acoustic oscillations Integrated Sachs-Wolfe effect SNe luminosity distance (fluctuations?) Cluster abundance Challenging control of systematics Less accurate, but systematics free Limited by cosmic variance SNe variability, evolution Do we understand clusters? Calibration Number of assumptions

4. R. Trotta - rxt@astro.ox.ac.uk Weak gravitational lensing Based on well-understood physics – Independent of mass-to-light relation – Probes geometry & growth of structures – Potential to achieve percent accuracy on w – Limited to z < 1 Systematic errors control – Image quality (0.1 to 1% distortions) – Gravitational-intrinsic correlations – Photo-z accuracy (tomography) – Non-linear effects Strategies – Large (10 4 -10 5 ) spectroscopic training sets – B-modes quantify the success of the correction – Use of radial information, cross-correlations between redshift bins – Combination of tomography/reconstruction with geometric test, checks for consistency

5. R. Trotta - rxt@astro.ox.ac.uk Baryonic acoustic oscillations A clean probe of geometry – Measures the angular diameter distance (transverse) and expansion rate (radial) – No known systematic effect can erase/mimick it – Based on well-known physical processes – Extends our window to z ~ 3 – In-built consistency check – Independent probe, curvature test, distinguish modifications of GR radial ) H(z) transverse ! D A (z) Requirements – Large and deep spectroscopic survey (GWFMOS) – Photo-z’s are insufficient Disadvantage – Lower statistical accuracy than weak lensing

6. Dark energy discovery space Observational techniques Growth of structures Clusters Weak lensing Standard rulers Acoustic oscillations SNe type Ia Tomography3D reconstruction geometric test + Planck CMB 2015 transverse (2D) + Planck CMB Photometry z = 1 transverse + radial (3D) + Planck CMB + SDSS + SNe Spectroscopy z=1 and z = 3 Accuracy on w 20% 10% 5% 1-2% 20% 10% 5% 1-2% systematics impact + SZ + WL calibration + Planck CMB 2009 2015

7. R. Trotta - rxt@astro.ox.ac.uk Proposals Dark Energy Survey, darkCAM – visible survey cameras, 4-5 bands – 5,000 – 10,000 sq deg to z » 1 Pan-STARRS – US Air Force, 4 telescopes planned – 3,000 sq deg in 5 bands Spectrographs – VIRUS, 200 sq deg, z » 3 – AAOmega, 500 to 1,000 sq deg – GWFMOS (HyperSuprime), z ~ 1 and z ~ 3 (Almost) everything you can think of – LSST, SKA (> 2015) GWFMOS darkCAM DES > 1 billion USD worth of proposals until 2015

8. Present and upcoming surveys 20062009201320142015 Imaging surveys Spectroscopy SNe WL BAO SZ BAO LSST ? 20’000 deg 2 out to z » 3 CFHT-LS 700 SNeDES 5’000 deg 2, 4% on w Pan-STARRS, full system deployed in 2009? VST – KIDS 1700 deg 2 DES 5’000 deg 2, 1-2% on w darkCAM, 1-2% on wCFHT-LS 170 deg 2 Pan-STARRS, full system deployed in 2009? GWFMOS 2’000 deg 2 @ z » 1 300 deg 2 @ z » 3 AAOmega 1’000 & 500 deg 2 ? VIRUS ? 200 deg 2 @ z » 3 Pan-STARRS, full system deployed in 2009? DES 5’000 deg 2, 5-20% on w darkCAM, 5-20% on w SPT

9. R. Trotta - rxt@astro.ox.ac.uk “Trust me, I’m a Bayesian!” Bayes factor B 01 RT (2005) Present Mismatch with prediction 00  Evidence in favour of w=-1 compared to -1/3 < w < -1  = 0.1not worth mentioning  = 0.01moderate  = 0.002strong Future

10. R. Trotta - rxt@astro.ox.ac.uk Closing remarks Preparing for the unexpected – What will be the most interesting questions in 2010? – Dark energy could surprise us again: maximise the discovery potential Developping know-how – Indispensable tools on the road to even larger surveys Making the most of the data – Statistical tools for optimal parameter inference – Model selection approach, surveys optimization Plenty of other science! – Next generation of surveys will provide extremely high quality data for numerous astronomical and astrophysical studies