LSST and Dark Energy

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LSST and Dark Energy

• LSST Directors Review
• SLAC
• March 8-9, 2006
• Tony Tyson
• Physics Department, Univ. of California, Davis

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LSST dark energy constraints

• Weak lensing correlations CMB
• Baryon acoustic oscillations (BAO) on large
  scales (k 10-1 h Mpc-1) CMB
• Power spectrum on very large scales
  (k 10-3 h Mpc-1)
• Supernovae to redshift 1(complementary to JDEM)
• Curvature the need for high-z data

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Challenges

• WL shear reconstruction errors
• Photometric redshift errors
• Suppress the power
• Boost the shot noise ? reduce number of modes
• Photometry errors (e.g. dust extinction)
• Lead to spurious power
• Contribute to photo-z errors
• Galaxy bias for BAO P(k,z)
• Alters the amplitude and shape of the PS

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Weak gravitational lensing
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sheared image
a 4GM/bc2
b
DS
DLS
q
shear
DLS
g q
4GM/bc2
DS
Gravity Cosmology change the growth rate of
mass structure
Cosmology changes geometric distance factors
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Cluster detection via WL shear
2-degree by 2-degree mass map of one of five DLS
fields. All four clusters examined in this field
have been verified with spectroscopy and X-ray
observations.
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2-parameter errors from WL
Two cosmologies Effect of joint analysis of
LSST 2-point and 3-point shear data Planck
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Angular size of galaxies
At the low surface brightness of LSST co-added
images, most galaxies at zlt3 are sufficiently
resolved in 0.7 seeing to reconstruct their
shear.
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20000 sq.deg WL survey shear power spectra
z1100
z3.2
z3.2
0.01 shear
z3.0
z0.6
z0.2
z0.6
0.001 shear
z0.2
0.001 shear
Blanco shear systematics floor
LSST shear systematics floor
Require shear error lt 0.0001
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Effect of baryons on DM spectrum
Zahn Knox 2004
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Subaru 10 sec exposures
Raw
de-trailed
PSF corrected
Single exposure in 0.65 arcsec seeing
13 arcmin (l 40)
ltsheargt 0.04
ltsheargt 0.000007
ltsheargt 0.07
ltsheargt 0.000013
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Residual Subaru shear correlation
Cosmic shear signal
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LSST WL Constraints on w0 and wa
Ma, Hu, Huterer (2005) Ma (private
communication)
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BAO as a Standard Ruler
CMB
Angular diameter distance Hubble parameter
RS150 Mpc
(Sound horizon at recombination)
(Angular radial scales)
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BAO Detection SDSS red galaxies
Eisenstein et al. (2005)
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Photo-z Errors Reduction of Modes
1/10 modes left!
Glazebrook Blake (2005)
Spectroscopic survey k lt 0.2 h-1Mpc
Photo-z survey sz 0.03 (1z)
Shot noise is amplified by the photo-z
suppression when recovering PS(k,m). P(k)
decreases toward small scales (kgt0.03h/Mpc), so
at high k3 the amplified shot noise may not be
tolerable and the modes have to be discarded.
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Prospects Power Spectrum
LSST
Errors are dominated by sample variance (volume)
at low-z and shot noise (number density) at
high-z. For photo-z surveys, sz reduces the
number of modes. See also Blake Bridle (2005).
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Very-Large-Scale Power Spectrum

• Binning Dk 0.16 k
• Inner error bars cubic geometric outer ones
  spherical harmonic mode counting
• Dotted lines caused by a step inflation
  potential that fits WMAP data (Peiris et al.
  2003)

Zhan et al. (astro-ph/0508119)
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LSST Constraints on w0 and wa BAO
Zhan Knox (astro-ph/0509260)
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Comparison of probes

• CMB priors WK0
• BAO constraints are competitive.
• A large rms photo-z error is tolerable the key
  is the uncertainty in sz.

Zhan Knox (astro-ph/0509260)
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CMB BAO Shear Tomography
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CMB BAO Shear Tomography
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CMB BAO Shear Tomography
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Curvature? The Need for High-z Data

• CMB priors
• High-z data not critical if WK is fixed
• High-z data crucial if WK unknown
• Behavior of the constraints depends on the survey
  and redshift errors
• See also Weller Albrecht (2001) and Linder
  (2005) for discussions on SNe data

1000 sq deg spectroscopic survey w0wa degrades
quite a bit if no high-z data even worse if WK
is unknown.
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LSST supernovae
Simulated light curves
Simulated Hubble diagram
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LSST supernovae vs BAO
LSST
Wang et al. 2006, AAS
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Eigenmodes of DE equations of state
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Summary of LSST probes of DE

• Deep and wide photo-z surveys such as the LSST
  survey can be a valuable probe of possible
  features in the matter power spectrum on very
  large scales.
• LSST can measure the angular diameter distance to
  percent level through BAO as well as weak lensing
  shear tomography.
• Photo-z BAO and WL constraints on dark energy
  equation of state parameters are sensitive to how
  accurately we know the photo-z error
  distribution.
• Given the same priors on photo-z errors, photo-z
  BAO is competitive with weak lensing shear
  tomography.
• To relax the flatness prior, high-z data are
  crucial.
• LSSTs million SNe provide a complementary
  cross-check
• Nonlinearities are not negligible. One must
  precisely calibrate the power spectrum in real
  and redshift spaces with N-body simulations (e.g.
  Seo Eisenstein 2003, 2005 Scoccimarro 2004
  Linder White 2005 Springel et al. 2005).

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Simulations of photometric redshifts
Photometric Redshifts LSST filter set,
performance prediction, simplest calibration
strategy (Connolly)
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12-band super photo-z training set
Together with angular correlations of galaxies,
this training set enables LSST 6-band photo-z
error calibration to better than required for
precision cosmology
Systematic error 0.003(1z) calibratable Need
3,000 spectroscopic redshifts.