A wide field imager for dark energy

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SNAP-L

• A wide field imager for dark energy
• and more !

Jean-Paul KNEIB LAM, Marseille, France
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The SNAP-L Mission

• SNAP-L is a 2m telescope with a wide field
  optical/near-IR camera and a 3D optical/near-IR
  spectrograph.
• SNAP-L is a project led by the Department of
  Energy (US particle physicist community) started
  in 1999
• with international partners
• France through the spectrograph development and
  scientific expertise (SN, WL) INSUIN2P3
• Sweden SN science
• Canada WL science
• Other countries interested and possibilities to
  have a stronger contribution in the project.

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SNAP-L the concept
A 2 meter class telescope, 3 mirror anastigmatic
design Provide a wide field flat focal plane, FOV
gt 0.7 square degrees Covering 350 to 1700
nm On a L2 orbit for stability and low background
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SNAP-L focal plane
spectrographe 3D IFU slicer visibleIR R100-200
3x3 , 0.35-1.7mm
9 filters 6 visibles 3 IR
Imager visible IR
pixel scale 0.10 arcsec/pixel (visible),
0.17 arcsec/pixel (NIR) 36 4kX4k CCDs 0.35-1mm
0.5 Gigapixels, 36 2kX2k HgCdTe 1-1.7
mm
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RD on optical/IR Detectors
Important RD funded by DOE for SNAP On the
detectors have reached the SNAP
requirements. Latest IR detector should go on
the new WFPC3 camera to be installed on HST
during SM4.
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SNAP IFU slicer spectrometer

• IFU concept based on slicer
• Compact and light (20x30x10 cm)
• Spectroscopy of SN and host in the same time
• Photometric calibration
• Spectro-z for photo-z calibration
• Demonstrator being developed at LAM

IR path
Visible IR
Wavelength coverage (?m) 0.35-0.98 0.98-1.70
Field of view 3.0" / 6.0" 3.0" / 6.0"
Spectral resolution, l/dl 70-200 70-100
Spatial resolution element (arc sec) 0.15 0.15
detectors LBL CCD 10 mm HgCdTe 18 mm
Efficiency with OTA and QE gt50 gt40
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The SNAP-L Mission

• SNAP-L is a dedicated mission to measure Dark
  Energy with
• SuperNovae and WL measurements (and possibly
  Baryon Acoustic Oscillation).
• SNAP-L will have a deep survey and a wide survey
• Both dedicated for SN and WL observation strategy
  but both useful for  other sciences 

Key advantages of SNAP-L PSF, image quality,
stable photometry Wide field, Depth, Large
wavelength coverage (both in visible and NIR with
9 filters), on board spectrograph.
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Why going in space?

• 0.1 angular resolution over wide field (0.7
  sq.degree)
• Near-infrared unfettered by atmospheric
  emission/absorption
• Continuous, year-round observation of selected
  fields
• Stability!

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Space-based imaging vs ground
GEMS
COMBO-17 (Brown et al. 2003)
100 galaxies per sq arcmin
35 galaxies per sq arcmin

• Space-based imaging has a significantly higher
  surface density
• of resolved sources, which can probe the matter
  density power
• spectrum at higher redshifts than will ever be
  feasible from the
• ground.

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SNAP Surveys
Survey Area(sq.deg) Depth(AB mag)
ngal(arcmin-2) Ngal Deep/SNe 10
30.4 250
107 Wide /WL 1000gt4000 28.1
100 108.5 Panoramic
7000-10000 26.7 40-50
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Point Source - 3?
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SNAP Deep Survey

• Base SNAP survey 7.5 square degrees near North
  ecliptic pole
• 3000x as large as ACS UDF to mAB30.4 in nine
  optical and IR bands.
• Provides 150 epochs over 22 months (each to
  mAB27.8) for time domain studies in all nine
  bands SNe, AGNs

Hubble Deep Field
GOODS Survey area
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SNe Systematic Control
SNe observation strategy Goal Observe 2000
hig-redshift SN in photometry and spectroscopy up
to z1.7 How 22-month survey covering 7.5
sq.degree, with 2400s exposure per field every 4
days. The 9 band photometry will allow to select
SN candidates for spectroscopy, and ensure
quality rest-frame photometry. 40 of the time
is reserved for on-board spectroscopy, with a
large fraction for zgt1 SNe. SN redshift determine
through the SiII broad line. NICMOS on HST has
shown that spectro-photometry calibration can
achieve better than 1 error
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SNAP Wide Area Survey

• 1000 sq.deg. wide survey the deep field, but
  discussion for extension to 4000 sq.deg.
• Roughly 1 year for 10002
• of observing time
• Four dithered 500 second exposures at each
  location sensitive to mAB28.1 (point source)
• Every field observed in all nine optical NIR
  filters

Hubble Deep Field
GOODS Survey area
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• WL 2-points stat What is measured?

ltg2gt0.01 ?82 ?1.6 zs1.4 q-(n2)/2

• Mass power spectrum normalisation
• Slope of the power spectrum
• Mean density parameter
• Redshift of the sources
• Ultimately Dark Energy constraints

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Lensing Mass Map
3D Mapping of the mass distribution. COSMOS
field as an example.

• green countours
• X-ray
• Color blobs
• optical/phot-z
• detection

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Ground/Space comparison

• Shear Calibration error estimate for a constant
  PSF
• Ground 0.7
• Space 0.1
• m is calibrated with realistic image
  simulation m5e-3.
• m depends on PSF stability and ellipticity

Waerbeke et al
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Ground/Space Comparison

• A space 4k sq.deg survey, is equivalent to a
  ground 20k sq. deg survey for similar photo-z
  bias.
• Space photo-z bias should 5 times better, a
  factor of 3 improvement in the FOM

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Photometric Redshift
NIR Filters are crucial for photo-z accuracy and
to reduce catastrophic failures (see Ilbert et
al 2006) Filter optimisation for photo-z in
progress, possibility to include U-band filter.
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The standard method -Results

• CFHT-LS deep field photo-z show that SED
  templates needs to be optimized !!!

Ilbert et al 2006
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Calibration - template optimization

• CFHT-LS optimize 4 templates with 2800
  spectroscopic z

Need of spectro-z Calibration. On-board
spectrograph can measure redshift in parallel of
the SN and WL survey (50 000 spectro-z per year
of WL observation ABlt24.5)
Optimized templates

• Initial
• templates

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Calibration - improvement
Calibration method is successful to remove
systematics. More spectro-z the better,
feasibility is on progress but is looking good.
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Dark Energy Constraints
Produce Good photo z Use 3 WL Methods Very
powerful
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what SNAP can also

• Dark energy
• SNII
• Galaxy clustering / baryon oscillations
• Galaxy clusters and their clustering
• Strong lensing
• Correlation with other surveys
• ISW, SZ, dark baryons

• Non-dark energy science
• Galaxy evolution
• Quasars and AGN
• Solar system objects
• Nearby galaxies, structure, stellar pops,
  globular clusters
• High-z objects
• MW structure stars

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Strong Lensing with SNAP-L

• Current example
• SL2S automatic search through the CFHT-LS for
  arcs and partial rings around elliptical galaxies
  (40 candidates out of the first 28 sq.degree)
  Follow-up with an ACS snapshot program.
• COSMOS 1.5 strong lenses in 1.7 sq deg.
• gt 10-40 thousands strong lensing system in
  SNAP-L WL survey.

Cabanac et al 2006
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Marshall et al 2006
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UDF Can see
Galaxies at z6
And has candidates up to z8 - similarly SNAP-L
will image these distant galaxies
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High-z galaxies Stiavelli et al 2004
Expect 100 000 zgt7 galaxies in the SNAP-L SN
surveys down to AB29. Unique way to map large
scale structure at zgt7 (faster than JWST) and
find rare objects (QSOs, strong lenses,
) SNAP-L can be seen as a survey telescope for
JWST.
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Probing the end of dark ages

• z3 quasars 200 400 per sq. deg
• Hundreds of z6 quasars
• Maybe 10 luminous quasars at z 9 10?

Xiaohui Fan
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Conclusion

• SNAP is a well advanced concept (RD well
  advanced and ready for integration) currently
  proposed in the NASA JDEM context, but JDEM
  contract is being re-discussed for an early
  launch (goal 2014).
• SNAP is dedicated to dark energy and will provide
  at least 2 surveys (AB30,28 point sources) for
  SN and WL but these can address many other
  sciences.
• France (CNES) through the spectrograph
  contribution is well involved, and other
  participation might be possible to become a
  stronger partner (telescope, WL data center and
  analysis )