Weak Lensing From Space

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Weak Lensing From Space
Jason Rhodes (JPL) January 7, 2005 Ohio State
University Conference on Gravitational Lensing,
Dark Matter and Dark Energy
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Weak Gravitational Lensing
In the absence of large-scale structure, light
beams from a galaxy follow the undistorted path.
Dark matter bends space and the light follows
the distorted path.
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Scientific Promise of WL

• Direct measure of dark matter distribution on
  various scales dark matter maps
• Constraints on ?M, s8, w, w complementing and
  breaking degeneracies present in other methods
  (SNe, CMB)

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HST WFPC2 STIS (1999-2003)

• Past
• Present
• Future

HST ACS (2004-20??)
SNAP/JDEM or something similar (2013?-??)
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Advantages of Space
Small and stable PSF ?larger number of resolved
galaxies ? reduced systematics
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Mass Resolution
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Limitations of Space

• Small field of view
• Only one facility--- HST
• 2 (or more) orders of magnitude more expensive

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Past Space Based Cosmic Shear Measurements

• Rhodes et al. 2000 Set upper limit in Groth
  Strip (WFPC2) 0.03 square degrees
• Rhodes et al. 2001 Marginal measurement in Groth
  Strip 0.03 square degrees
• Refregier et al. 2002 Measurement of s8 and
  cosmic shear in the Medium Deep Survey (WFPC2)
  0.3 square degrees
• Casertano et al. 2003 Measurement of cosmic shear
  in the Medium Deep Survey (WFPC2) 0.5 square
  degrees
• Hämmerle et al. 2002 Marginal detection of cosmic
  shear in STIS Parallel images 0.02 square degrees
• Rhodes et al. 2004 Measurement of s8 and cosmic
  shear in the STIS parallel images 0.25 square
  degrees
• Heymans et al. 2004 Measurement of s8 and cosmic
  shear in the GEMS Survey 0.25 square degrees

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Current Observational Status

• Shear Correlation Function
• measure of the amplitude of mass fluctuations
  ?8(?m/0.3)0.51

From Heymans et al 2004
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s8
Heymans et al. 2004
Massey et al. 2004

• ? Moderate disagreement
• among cosmic shear measurements
• This could be due to residual systematics
• Agreement on average with CMB constraints
• moderate inconsistency with cluster abundance
  (systematics or new physics?)

Rhodes et al. 2003
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New HST Surveys
GEMS
UDF
GOODS
COSMOS
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COSMOS

• 2 square degrees
• Single orbit F814(I) ACS images
• 80 resolved galaxies per square arcmin
• versus 30 from the ground
• Unique combination of area, depth and resolution
• Opens door for unprecedented dark matter maps

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COSMOS Cycle 12 Images
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COSMOS Mass Map
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Time Dependent PSF
The PSF pattern is time dependent
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SNAP/JDEM --- The Future

• PI Saul Perlmutter/ Michael Levi
• Joint NASA/DOE project
• 2014 ??? launch
• 3 year primary mission
• 3 year GO mission
• Detect 2000 SN to z1.7
• Follow light curves

• Measure cosmic equation of state wp/?
• Measure w'

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SNAP Wide Survey

• Wide Weak Lensing Survey
• 1000 square degrees per year
• 9 optical and NIR filters (350nm -1.7 µm)
• AB 26.5
• Neff 100 arcmin-2
• 350 million galaxies per year
• ?z?0.1
• Redshift bin accuracies at sub percent level
• Unprecedented dark matter maps and cosmological
  parameter determinations

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Dark Matter Power Spectrum

• The DM power spectrum is a remarkably powerful
  quantity
• provides direct probe of DM distribution free
  from bias and astrophysical assumptions
• probes complexities of
• non-linear regime
• form constraints equation of state (wp/?)
  modulo some degeneracy between ?M and w

Wide survey
Non-linear physics
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Shear Bispectrum
8 components!
Three point correlation function tests non
Gaussianity
see Takada and Jain (2003)
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Cross Correlation Cosmography (CCC)

• Shear at z1 and z2 given by integral of growth
  function distances over lensing mass
  distribution.

zf
z1
lensing mass
z2
Dominating systematic becomes photo-z error, not
PSF
see (Jain Taylor 03 Bernstein Jain 03)
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Dark Energy Constraints From SNAP
Central ? is ?CDM prediction SUGRA is a
supergravity model
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Complementarity With the Ground

• Ground can find clusters, space can measure
  masses
• Ground can survey whole sky, space can probe
  deeper in selected areas
• Space data with lower systematics and higher
  redshift accuracy can calibrate ground surveys

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Fundamental Limit From the Ground
100 deg2
1000 deg2
10000 deg2
For areas gt 100 deg2 ground based surveys will
be limited by PSF systematics