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Transcript
LSST and JDEM as Complementary
Probes of Dark Energy
Tony Tyson, Andy Connolly, Zeljko Ivezic,
James Jee, Steve Kahn, Sam Schmidt,
Don Sweeney, Dave Wittman, Hu Zhan
JDEM SCG Telecon
November 25, 2008
Outline
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Science drivers
Hardware implementation
Systematics
Simulations
Synergy with JDEM
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LSST survey of 20,000 sq deg
• 4 billion galaxies with redshifts
• Time domain:
1 million supernovae
1 million galaxy lenses
5 million asteroids
new phenomena
3
LSST Survey
 6-band Survey: ugrizy 320–1100 nm
Frequent revisits: grizy
 Sky area covered:
>20,000 deg2
0.2 arcsec / pixel
 Each 10 sq.deg field reimaged ~2000 times
 Limiting magnitude:
27.6 AB magnitude @5s
25 AB mag /visit = 2x15 seconds
 Photometry precision: 0.005 mag requirement
0.003 mag goal
Key LSST Mission: Dark Energy
Precision measurements of all dark energy
signatures in a single data set. Separately
measure geometry and growth of dark matter
structure vs cosmic time.
 Weak gravitational lensing correlations
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(multiple lensing probes!)
Baryon acoustic oscillations (BAO)
Counts of dark matter clusters
Supernovae to redshift 0.8
(complementary to JDEM)
Probe anisotropy
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6
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3200 megapixel camera
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Relative system throughput (%)
LSST six color system
Includes sensor QE, atmospheric
attenuation, optical transmission functions
Wavelength (nm)
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The LSST Focal Plane
Wavefront
Sensors (4
locations)
Guide
Sensors (8
locations)
Wavefront Sensor Layout
2d
Focal plane
Sci CCD
40 mm
Curvature Sensor Side View Configuration
3.5 degree Field of
View (634 mm
diameter)
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LSST reconstruction pipeline simulator
xi  ( AT  A) 1  AT  f o
 xi
Perturbations
Get correction vector by solving
Normal equation. (A: sensitive
matrix, f0: error vector.)
 2W  
I1
1 I1  I 2
z I 1  I 2
Wedge
I2
n
0
x
WCS processing: get the perturbation
wavefronts
Get intra and extra focal image intensities.
* Tools used for simulations and calculations: Zemax
Matlab
12
Active optics
Correct for perturbations due to thermal and mechanical distortions
Each optic has 6 dof (decenter, defocus, three euler angles)
Perturbations are placed on the three mirrors using a
Zernike expansion to simulate the possible residual
control system errors each mirror can have an arbitrary amplitude
code goes up to 5th order polynomials
e.g. Mirror Defocus
Perturbation spectrum
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FWHM Allocation & Budget meets SRD Requirements
Margin available
Some Telescope
Thermal Effects Included
No Explicit Camera Allocation
For Thermal Effects
14
The LSST CCD Sensor
16 segments/CCD
200 CCDs total
3200 Total Outputs
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Flatness metrology
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The LSST site in Chile
photometric
calibration telescope
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Seeing distribution
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There are 24 LSSTC US Institutional Members
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Brookhaven National Laboratory
California Institute of Technology
Carnegie Mellon University
Columbia University
Google Inc.
Harvard-Smithsonian Center for
Astrophysics
Johns Hopkins University
Las Cumbres Observatory
Lawrence Livermore National
Laboratory
National Optical Astronomy
Observatory
Princeton University
Purdue University
 Research Corporation
 Rutgers University
 Stanford Linear Accelerator
Center
 Stanford University –KIPAC
 The Pennsylvania State University
 University of Arizona
 University of California, Davis
 University of California, Irvine
 University of Illinois at
Champaign-Urbana
 University of Pennsylvania
 University of Pittsburgh
 University of Washington
+ IN2P3 in France
Funding: Public-Private Partnership
NSF, DOE, Private
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LSST imaging & operations simulations
Sheared HDF raytraced +
perturbation + atmosphere +
wind + optics + pixel
Figure : Visits numbers per field for the 10 year simulated survey
LSST Operations, including real
weather data: coverage + depth
Performance verification using Subaru imaging
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10-year simulation:
limiting magnitudes per 30s visit in main survey
1 visit = 2 x 15 sec exposures
Opsim5.72 Nov 2008
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10-year simulation:
number of visits per band in main survey
Opsim5.72 Nov 2008
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LSST and Cosmic Shear
Ten redshift
bins yield 55
auto and
cross spectra
useful range
baryons
+ higher order
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2-D Baryon Acoustic Oscillations
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LSST Precision on Dark Energy [in DETF language]
Combining techniques breaks degeneracies.
Joint analysis of WL & BAO is less affected by the systematics
26
Critical Issues

WL shear reconstruction errors
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Show control to better than required precision
using existing new facilities 
Photometric redshift errors
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Develop robust photo-z calibration plan 
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Undertake world campaign for spectroscopy ()
Photometry errors

Develop and test precision flux calibration
technique 
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Residual shear correlation
Test of shear systematics:
Use faint stars as proxies for
galaxies, and calculate the
shear-shear correlation after
correcting for PSF ellipticity
via a different set of stars.
Cosmic shear signal
Stars
Compare with expected
cosmic shear signal.
Conclusion: 200 exposures
per sky patch will yield
negligible PSF induced shear
systematics. Wittman (2005)
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HST ACS data
LSST:
Gold sample:
4 billion galaxies
i<25 (S/N=25),
out of 10 billion
detected.
56/sq.arcmin
~40 galaxies
per sq.arcmin
used for WL
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residual galaxy shear correlation
Single 10 sq.deg field full depth
Galaxy residual shear
error is shape shot
noise dominated.
Averages down like
1/N fields to the
systematic floor.
Survey of 20,000
sq.deg will have N ~
2000 fields in each
red band r, i, z
Simulation of
0.6” seeing.
J. Jee 2008
30
IMAGE SIMULATIONS
Extended
Sources
Milkyway
Transients
Solar
System
Generate the seed catalog as
required for simulation. Includes:
Metadata
Size
Position
Color
Type
Brightness
Proper motion Variability
Introduce shear parameter from
cosmology metadata
All Sky
Database
Defects
Base
Catalog
Cosmology
Instance Catalog
Generation
Source Image
Generation
Atmosphere
Telescope
Photon
Propagation
Operation
Simulation
DM Data
base load
simulation
Generate
per FOV
Operation
Simulation
Camera
Defects
Formatting
Generate per
Sensor
DM Pipelines
Calibration
Simulation
LSST Sample Images and Catalogs
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Input catalog for simulations
 Millennium Simulations
Kitzbichler and White (2006)
o
o
o
o
o
o
o
o
6 fields, 1.4x1.4 deg per field
6x106 source per catalog
Based on Croton et al (2006) and
De Lucia and Blaizot (2006)
models
r<26 magnitude limit
z<4 redshift limit
BVRIK Johnson and griz SDSS
Estimated u and y passbands
Type and size included
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Photo-z Simulations
Abdalla etal. 2008
J=23.4 10 sigma
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Calibrating photometric redshifts
Cross-correlation LSS-based
techniques can reconstruct the
true z distribution of a photo-z
bin, even with spectroscopy of
only the brightest galaxies at
each z.
These techniques meet
LSST requirements with
easily attainable
spectroscopic samples,
~104 galaxies per unit z.
Newman 2008
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Combining four LSST probes
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Testing more general DE models
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Probe anisotropy
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multiple probes of dark energy
• WL shear-shear tomography
• WL bi-spectrum tomography
• Distribution of 250,000 shear peaks
• Baryon acoustic oscillations
• 1 million SNe Ia, z<1 per year
• Low l, 2p sky coverage: anisotropy?
3x109 galaxies, 106 SNe
• probe growth(z) and d(z) separately
• multiply lensed AGNs and SNe
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JDEM-LSST Complementarity
 JDEM+LSST in 20,000 sq.deg and in fifty 10 sq.deg
deep drilling fields
 Estimated cosmological constraints using LSST+JDEM
 Optimum strategy for joint DE mission risk reduction
 Priorities for max complementarity and cost
effectiveness
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JDEM+LSST
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JDEM-LSST Priorities
1.
2.
3.
4.
5.
Two IR bands from space. Deep, wide. Helps photo-z
plus lots of astronomy (galaxy evolution, stellar)
JDEM spectroscopic BAO complements LSST 2-D BAO
JDEM coverage of same 20,000 sq.deg (see #1)
Four near IR bands from space, closing the zY gap
JDEM WL coverage of some of LSST’s survey area
Need quantitative modeling for joint design mission. It will be
useful to simulate the increase in FoM for each priority
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extra slides
43
Requirement of integrated 50 galaxies per sq.arcminute: green line in the
following plot. The corresponding 10 sigma limiting magnitudes in r and i are:
r=25.6 i=25.0 AB mag
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WL shear power spectrum and statistical errors
Signal
LSST: fsky = 0.5, ng = 40
SNAP: fsky = 0.1, ng =100
RMS intrinsic contribution
to the shear σg= 0.25
(conservative).
No systematics!
Noise
SNAP
LSST
Jain, Jarvis, and Bernstein 2006
gastrophysics
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Trade with depth and systematics
LSST only
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Comparing HST with Subaru
ACS: 34 min (1 orbit)
PSF: 0.1 arcsec (FWHM)
2 arcmin
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Comparing HST with Subaru
Suprime-Cam: 20 min
PSF: 0.52 arcsec (FWHM)
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Galaxy ellipticity systematics in the SRD
Specification: The median LSST image (two per
visit) must have the median E1, E2, and Ex
averaged over the FOV, less than SE3 for 1 arcmin,
and less than SE4 for 5 arcmin. No more than EF2
% of images will exceed values of SE5 for 1 arcmin,
nor SE6 for 5 arcmin
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DETF FoM vs Etendue-Time
Separate DE Probes
Combined
JDEM+LSST will be even better
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