Surveys of Dark Energy: Challenges and Prospects

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Surveys of Dark EnergyChallenges and Prospects

• Cosmology post WMAP/2dF/SDSS/
• The Dark Energy Survey
• Photometric redshifts, and cross-talk with
  cosmic probes
• The future of the local universe

• Ofer Lahav
• University College London

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Evidence for Dark Energy

• SN Ia
• CMB
• LSS Baryonic Oscillations
• Cluster counts
• Weak Lensing
• Integrated Sachs Wolfe
• Physical effects
• Geometry
• Growth of Structure

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The Chequered History of theCosmological
Constant ?
The old CC problem Theory exceeds observational
limits on ? by 10120 ! The new CC problem Why
are the amounts of Dark Matter and Dark Energy
so similar?
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Globalisation and the New Cosmology

• How is the New Cosmology affected by
  Globalisation?
• Recall the Cold War era
• Hot Dark Matter/top-down (East)
• vs. Cold Dark Matter/bottom-up (West)
• Is the agreement on the concordance model a
  product of Globalisation?

OL, astro-ph/0610713
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• Matter and Dark Energy tell space how to
  curve
• ?k 1 -?m - ??

Curvature Matter
Dark Energy(Vacuum)
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• Matter and Dark Energy tell space how to
  curve
• ?k 1 -?m - ??

Curvature Matter
Dark Energy(Vacuum)
OR modified curvature
?k ?? 1 -?m
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• The Universe is accelerating at present if
• q0 ?m/2 - ?? lt 0
  
• 
  

e.g. For ?m 0.3 and ?? 0.7 ?k 0 (the
Universe is flat) and the Universe is
accelerating (but only recently, zlt0.7)
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Spherical Collapse

• d2r/dt2 -GM/r2 (?/3) r

cf. Newton-Hooke force cf. Inflation For the
mass of the Local Group (MWM31) the forces are
equal at r 1.3 Mpc
Dark Energy also affects the virialization radius
the collapsed object (OL et al. 91 Maor OL 05)
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Probing Dark Matter Dark Energy

• Through the history of the expansion rate
• H2(z) H20 ?M (1z) 3 ?DE (1z) 3 (1w)
  (flat Universe)
• matter
  dark energy (constant w)
• P w ?
• Comoving distance
  r(z) ? dz/H(z)
• Standard Candles
  dL(z) (1z) r(z)
• Standard Rulers
  dA(z) (1z)?1 r(z)
• The rate of growth of structure also determined
  by H(z) and by any modifications of gravity on
  large scales

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Baryon Wiggles as Standard Rulers
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DUNE Dark UNiverse Explorer

• Mission baseline
• 1.2m telescope
• FOV 0.5 deg2
• PSF FWHM 0.23
• Pixels 0.11
• GEO (or HEO) orbit
• Surveys (3-year initial programme)
• WL survey 20,000 deg2 in 1 red broad band, 35
  galaxies/amin2 with median z 1, ground based
  complement for photo-zs
• Near-IR survey (J,H). Deeper than possible from
  ground. Secures z gt 1 photo-zs
• SNe survey 2 60 deg2, observed for 9 months
  each every 4 days in 6 bands, 10000 SNe out to z
  1.5, ground based spectroscopy

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Imaging Surveys
proposed
moderate
5000?
45
VST/VISTA
2010-2015?
proposed
moderate
DUNE
21?
20000? (space)
2012-2018?
Y. Mellier
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US Dark Energy Task Force Recommendations

• An immediate start of a near-term program (which
  we call Stage III) designed to advance our
  knowledge of dark energy and prepare for the
  ultimate Stage IV program, which consists of a
  combination of large survey telescopes and/or a
  space mission.
• cf. PPARC and ESO/ESA reports

Advocate a Figure of Merit
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DETF FoM / 1/ellipse area
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The Dark Energy Survey

• Study Dark Energy using
• 4 complementary techniques
• I. Cluster Counts
• II. Weak Lensing
• III. Baryon Acoustic Oscillations
• IV. Supernovae
• Two multi-band surveys
• 5000 deg2 g, r, i, z
• 40 deg2 repeat (SNe)
• Build new 3 deg2 camera
• and data management system
• Survey 2010-2015 (525 nights)
• Response to NOAO AO

Blanco 4-meter at CTIO
300,000,000 photometric redshifts
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The DES Collaboration
Fermilab J. Annis, H. T. Diehl, S. Dodelson, J.
Estrada, B. Flaugher, J. Frieman, S. Kent, H.
Lin, P. Limon, K. W. Merritt, J. Peoples, V.
Scarpine, A. Stebbins, C. Stoughton, D. Tucker,
W. Wester University of Illinois at
Urbana-Champaign C. Beldica, R. Brunner, I.
Karliner, J. Mohr, R. Plante, P. Ricker, M.
Selen, J. Thaler University of Chicago J.
Carlstrom, S. Dodelson, J. Frieman, M. Gladders,
W. Hu, S. Kent, R. Kessler, E. Sheldon, R.
Wechsler Lawrence Berkeley National Lab N. Roe,
C. Bebek, M. Levi, S. Perlmutter University of
Michigan R. Bernstein, B. Bigelow, M. Campbell,
D. Gerdes, A. Evrard, W. Lorenzon, T. McKay, M.
Schubnell, G. Tarle, M. Tecchio NOAO/CTIO T.
Abbott, C. Miller, C. Smith, N. Suntzeff, A.
Walker CSIC/Institut d'Estudis Espacials de
Catalunya (Barcelona) F. Castander, P. Fosalba,
E. Gaztañaga, J. Miralda-Escude Institut de
Fisica d'Altes Energies (Barcelona) E.
Fernández, M. Martínez CIEMAT (Madrid) C. Mana,
M. Molla, E. Sanchez, J. Garcia-Bellido University
College London O. Lahav, D. Brooks, P. Doel, M.
Barlow, S. Bridle, S. Viti, J. Weller University
of Cambridge G. Efstathiou, R. McMahon, W.
Sutherland University of Edinburgh J. Peacock
University of Portsmouth R. Crittenden, R.
Nichol, R. Maartnes, W. Percival University of
Sussex A. Liddle, K. Romer
plus postdocs and students
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The Dark Energy Survey UK Consortium (I)
PPARC funding O. Lahav (PI), P. Doel, M.
Barlow, S. Bridle, S. Viti, J. Weller (UCL),
R. Nichol (Portsmouth), G. Efstathiou, R.
McMahon, W. Sutherland (Cambridge) J. Peacock
(Edinburgh) Submitted a proposal to PPARC
requesting 1.7M for the DES optical design.
In March 2006, PPARC Council announced that
it will seek participation in DES. PPARC
already approved 220K for current RD. (II)
SRIF3 funding R. Nichol, R. Crittenden, R.
Maartens, W. Percival (ICG Portsmouth) K.
Romer, A. Liddle (Sussex) Funding the optical
glass blanks for the UCL DES optical work These
scientists will work together through the UK DES
Consortium. Other DES proposals are under
consideration by US and Spanish funding
agencies.

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The Dark Energy Survey Camera DECam
DECam will replace the prime focus cage
4m Blanco telescope
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Supernovae Ia

• Geometric Probe of Dark Energy
• Repeat observations of 40 deg2 , using 10 of
  survey time
• 1900 well-measured SN Ia
• lightcurves, 0.25 lt z lt 0.75
• Larger sample, improved z-band response compared
  to ESSENCE, SNLS address issues they raise
• Improved photometric precision via in-situ
  photometric response measurements

SDSS
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Background sources
Dark matter halos
Observer

• Statistical measure of shear pattern, 1
  distortion
• Radial distances depend on geometry of Universe
• Foreground mass distribution depends on growth of
  structure

A. Taylor
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DES Forecasts Power of Multiple Techniques
Assumptions Clusters SPT-selected, ?80.75,
zmax1.5, WL mass calibration (no clustering
self-calibration) Mass-observable power-law
w/ Lognormal spread BAO lmax300 WL
lmax1000 (no bispectrum or galaxy-shear) Statist
icalphoto-z systematic errors only Spatial
curvature, galaxy bias marginalized Planck CMB
prior
w(z) w0wa(1a) 68 CL


Ma, Weller, Huterer, etal
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DES Figure of Merit
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Photo-z WL BAO - SNIa cross talk

• Approximately, for a photo-z slice
• (?w/ w) a (?z/ z) a (?z/z) Ns-1/2
• gt the target accuracy in w
• and photo-z scatter ?z dictate the number of
  required spectroscopic redshifts
• Ns 105-106

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Photometric redshifts
z3.7
z0.1
Probe strong spectral features (e.g. 4000
break)

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ANNz - Artificial Neural Network
z f(m,w)

Output redshift
Input magnitudes
Collister Lahav 2004
http//www.star.ucl.ac.uk/lahav/annz.html
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Training on 13,000 2SLAQGenerating with
ANNz Photo-z for 1,000,000 LRGs MegaZ-LRG
?z 0.046
Collister, Lahav, Blake et al., astro-ph/0607630
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Excess Power on Gpc Scale?
Blake et al. 06
Padmanabhan et al. 06
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DES and VDES
DES (griz)
DESVISTA(JK)
VISTA J (lt21) and K (lt19) would improve photo-z
by a factor of 2 for zgt 1
F. Abdalla, M. Banerji, OL, H. Lin, et al.
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DES and a Dark Energy Programme

• 4-5 complementary probes
• Survey strategy delivers substantial DE science
  after 2 years
• Relatively modest ( 20-30M), low-risk,
  near-term project with high discovery potential
• Synergy with SPT and VISTA on the DETF Stage
  III timescale
• Scientific and technical precursor to the more
  ambitious Stage IV Dark Energy projects to
  follow LSST and JDEM

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The Future of the Local Universe?m 0.3
LCDM a 1 (t 13.5 Gyr)
LCDM a 6 (t 42.4 Gyr)
OCDM a 1 (t 11.3 Gyr)
OCDM a 6 (t 89.2 Gyr)
Hoffman, Dover, Yepes, OL
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Some Outstanding Questions

• Vacuum energy
• (cosmological constant, w -1.000 after
  all?)
• Dynamical scalar field?
• Modified gravity?
• Why ??/?m 3 ?
• Non-zero Neutrino mass lt 1eV ?
• The exact value of the spectral index n lt
  1 ?
• Excess power on large scales?
• Is the curvature zero exactly ?

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Extra Slides
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Expected performance of DECAM, Blanco, and CTIO
site
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DeCamOptical Lay Out
C1
C2
C3
C4
C5
978mm
Filter
1870mm
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Sources of uncertainties

• Cosmological (parameters and priors)
• Astrophysical (e.g. cluster M-T, biasing)
• Instrumental (e.g. seeing)

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MegaZ-LRG Angular power spectra


Blake, Collister, Bridle Lahav, astro-ph/0605303
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Blanco Telescope

• 4m diameter equatorial mount telescope.
• Located at altitude of 2200m at Cerro Tololo
  Inter-American Observatory (CTIO) , Chile
  (Lat. 30o 10 S, Long. 70 o 49 W).