Future observational prospects for dark energy

1
Future observational prospectsfor dark energy
Roberto Trotta Oxford Astrophysics Royal
Astronomical Society
2
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

Seljak et al 2005
Jarvis et a 2005
3
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

4
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 lt 1
• Systematic errors control
• Image quality (0.1 to 1 distortions)
• Gravitational-intrinsic correlations
• Photo-z accuracy (tomography)
• Non-linear effects

• Strategies
• Large (104-105) 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
Baryonic acoustic oscillations
transverse ! DA(z)

• 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)

• Requirements
• Large and deep spectroscopic survey (GWFMOS)
• Photo-zs are insufficient
• Disadvantage
• Lower statistical accuracy than weak lensing

6
Dark energy discovery space
systematics impact
Observational techniques
2015
7
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 (gt 2015)

darkCAM
DES
GWFMOS
gt 1 billion USD worth of proposals until 2015
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Present and upcoming surveys
SNe
LSST ? 20000 deg2 out to z 3
Imaging surveys
WL
BAO SZ
2006
2009
2013
2014
2015
GWFMOS 2000 deg2 _at_ z 1 300 deg2 _at_ z 3
AAOmega 1000 500 deg2 ?
Spectroscopy
BAO
VIRUS ? 200 deg2 _at_ z 3
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Trust me, Im a Bayesian!
Bayes factor B01
Mismatch with prediction
w
w0
Evidence in favour of w-1 compared to -1/3 lt w
lt -1 ? 0.1 not worth mentioning ?
0.01 moderate ? 0.002 strong
RT (2005)
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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