Dark Energy Survey
Sloan Digital Sky Survey
Thank many people in DES and SDSS
(McMahon, Sullivan, Lampeitl, Smith, Campbell)
My one slide on Dark Energy!
Strong evidence for “something” (last decade)
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Type Ia Supernovae
Cosmic Microwave Background
Large Scale Structure (BAO & ISW)
Gravitational Lensing
Critical questions (next decade)
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Is w(z) = -1 ?
Is there curvature? Non-gaussianity?
Is GR sufficient on large scales?
Can we control the systematic uncertainties?
Supernovae as Standard Candles
Peak brightness correlates
with decline rate & color
•  Variety of algorithms for
modeling these correlations
•  After correction, σ~ 0.16 mag
(~8% distance)
•  Color correction is larger than
the stretch corrections
Decade since discovery
•  Substantial increases in both quantity and quality of SN Ia
data: from several tens of relatively poorly sampled light
curves to many hundreds of well-sampled, multi-band light
curves from rolling surveys
•  Extension to previously unexplored redshift ranges: z>1
and 0.1<z<0.3
•  Extension to previously underexplored rest-frame
wavelengths (NIR)
•  Vast increase in spectroscopic data
•  Identification of SN Ia subpopulations (host galaxies)
•  Entered the systematic error-dominated regime, but with
pathways to reduce sys. errors
Frieman, et al (2008); Sako, et al (2008)
Results today from 2005 season
Kessler, et al 09; Lampeitl et al 09; Sollerman et al 09
SDSS II SN Survey Goals
•  Obtain few hundred high-quality* SNe Ia light curves in
the `redshift desert’ z~0.05-0.4 for continuous Hubble
diagram
•  Well-observed sample to anchor Hubble diagram, train
light-curve fitters, and explore systematics of SN Ia
distances
•  Rolling search: determine SN/SF rates/properties vs.
z, environment
•  Rest-frame u-band templates for z >1 surveys
•  Large survey volume: rare & peculiar SNe, probe
outliers of population
*high-cadence, multi-band, well-calibrated
6
H.-J. Seo
B. Hayden
Spectroscopic follow-up telescopes
R. Miquel, M. Molla, L. Galbany, J. Nordin
Searching For Supernovae
Search
g
Template
Difference
•  2005
–  190,020 objects
scanned
–  11,385 unique
candidates
–  130 confirmed Ia
•  2006
r
–  14,441 scanned
–  3,694 candidates
–  193 confirmed Ia
•  2007
–  175 confirmed Ia
• Positional match to remove movers
• Insert fake SNe to monitor efficiency
i
SDSS SN Photometry
9
Holtzman
etal (2008)
B. Dilday
500+ spec confirmed SNe Ia + 87 conf. core collapse plus
~300 (soon ~1000) photometric Ia’s with host z’s (SDSS-III)
Correct Distance
Estimates for
Brightness-decline
relation and dust
extinction
MLCS2k2 Light-curve
Templates Jha, etal (2007)
∆ <0: bright, broad
∆ >0: faint, narrow,
redder
time-dependent model “vectors”
trained on Low-z SNe
fit parameters
Time of maximum
distance modulus
dust
stretch/decline rate
1st year Cosmology
103 SNe Ia from
first season that
pass stringent
light-curve
quality cuts
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Kessler etal (2009)
Lampeitl etal (2009)
Sollerman etal (2009)
q0 = -0.34 (97%)
(intrinsic scatter
only 0.08mag)
Cosmological Constraints
Only look at measurements at z<0.4
ISW (z<0.4)
Peacock et al Flat wCDM
W
w= -1 (15% stat & sym)
w=-0.85±0.18 Ωm=0.27±0.09
SNe
BAO
All data
MLCS
w = −0.76 ± 0.07(stat) ± 0.12(syst)
SALT
w = −0.96 ± 0.06(stat) ± 0.12(syst)
Everything consistent with
LCDM
Diagnosis:
•  Large difference in Light-curve
model in U-band
•  Use of prior on extinction in
MLCS
A Tale of Two Fitters
MLCS:
•  U-band model trained only on low-redshift (observer-frame) Uband data (calibration, atmospheric variations)
•  Assumes all excess color due to dust extinction (some of it must
be); dust prior dominates at high-redshift
SALT:
•  Global fit for color/dust parameter β: minimizing Hubble-scatter
can lead to bias
•  Trend toward bluer colors at high-z: if allow β(z), see strong
trend with redshift
Retrain and refine the models with newer data. Model
independent methods (new ideas?)
Dark Energy Survey (DES)
•  Proposal:
–  Perform a 5000 sq. deg.
survey of the southern
galactic cap
–  Measure dark energy with
4 complementary
techniques
•  New Instrument:
–  Replace the PF cage with
a new 3deg FOV, 520
Mega pixel optical CCD
camera + corrector
•  Time scale:
–  Instrument Construction
2008-2011
•  Survey:
–  525 nights during Oct.–
Feb. 2011-2016
Use the Blanco
4m Telescope
at the Cerro Tololo
Inter-American
Observatory (CTIO)
DES Participating Institutions
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Fermilab
University of Illinois at Urbana-Champaign
University of Chicago
Lawrence Berkeley National Laboratory
University of Michigan
NOAO/CTIO
Spain-DES Collaboration:
Institut d'Estudis Espacials de Catalunya (IEEC/ICE), Institut de Fisica
d'Altes Energies (IFAE), CIEMAT-Madrid:
United Kingdom-DES Collaboration:
University College London, University of Cambridge, University of
Edinburgh, University of Portsmouth, University of Sussex
The University of Pennsylvania
Brazil-DES Consortium
The Ohio State University
Argonne National Laboratory
12 participating institutions and >100 participants
DES Funding from DOE, NSF, STFC (UK), Ministry of Education and Science
(Spain), FINEP (Brazil), and the Collaborating Institutions
The DES Instrument: DECam
F8 Mirror
Filters
Shutter
3556 mm
CCD
Read out
Hexapod
Optical
Lenses
1575 mm
DES CCDs
Thinned CCD
LBNL high resistivity
100
Quantum Efficiency (%)
•  62 2kx4k fully
depleted CCDs
520 Megapixels
•  Excellent red
sensitivity
•  Developed by LBNL
Deep Depleted
90
80
70
60
50
40
30
20
10
0
300
400
500
600
700
800
Wavelength (nm)
900
1000
1100
Five lenses are now being
polished & coated at SESO
C5
C2
C1
Delivery to UCL in Feb 2010
Prototype testing
44 CCD installed
On sky testing with 1 CCD on the CTIO 1m
Fermilab: on-sky Oct 2011
The Surveys
•  Two multi-band surveys
5000 deg2 g, r, i, z, Y
~20 deg2 repeat (SNe)
r < 24
300,000,000 photometric
redshifts within a volume
of 23 (Gpc/h)3, out to z ~ 1.5
Blanco 4-meter at CTIO
4000 deg2
Stripe82
Synergy with VISTA (VHS)
DES+VISTA(8 filters)
Banerji et al. 0711.1059
Photo-z
with
ANNz
DES+VISTA would improve photo-z by a factor of 2 for z> 1
(δw/ w) = 5 (δz/ z) = 5 (σz/z) Ns-1/2
photo-z scatter σz dictate the number of required
spectroscopic redshifts eg. Ns =105-106
DES Forecast
Constraints
DETF FoM
• DES+Stage II combined = Factor 4.6 improvement over Stage II combined
•  Systematics remain!
Clusters: Synergy with SPT
•  10m, bolometer array (150, 250, 270 GHz)
• Detect ~10,000 clusters through Sunyaev-Zel’dovich effect
•  Measure photo-z’s to ~ 1.5
•  Mass from optical, SZ and lensing signals
Supernovae I
•  Use 10% of photometric
time, most of the nonphotometric time: 5 visits per
lunation in riz
•  Thousands of well-measured
SN Ia lightcurves to z~1.
Supernovae II
•  Red-sensitive CCD allow for
redder rest-frame colors and push
to higher z
•  Extensive simulations are ongoing to define the best SN survey
(end-to-end)
•  4% error on w0 for cosmology
sample
SNe Systematics: Color & Dust
•  Better to probe restframe red (i-band) or IR
(YJHK)
•  Interesting synergy with
VIDEO
–  Will target same field
–  Could sync obs to
get IR colors for
~6deg2
–  ~200 SNIa’s to
z~0.5 with
restframe Y-band
Wood-Vasey et.al 2008
Bernstein, Sullivan, Jarvis
Estimate ~85 nights
on world telescopes
DES Status
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Low-risk, near-term (2011-16) project with high discovery potential
Survey strategy delivers substantial DE science after 2 years
Synergy with SPT and VISTA (VHS and VIDEO)
Science collaboration now formed and working on final survey
strategies and data challenges (>100 scientists)
•  Total cost is relatively modest (~ $30M)
  DES in the US President budget request for FY08, FY09
  DOE approved for CD3a (last one)
  NSF contribution to data management
  International contributions in science and hardware
Lessons and work
•  SDSS is done, systematics limited
•  new ideas for analysing data?
•  better ways of flagging transients
•  less biased and more imaginative follow-up
•  DES is in construction (Oct 2011 on sky!)
•  exploit redder passbands
•  increased photometric accuracy
•  mature simulations
The End
Photometric redshifts
z=0.1
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Probe strong
spectral features
(e.g. 4000 break)
z=3.7
DES Forecast
Constraints
DETF FoM
• DES+Stage II combined = Factor 4.6 improvement over Stage II combined
• Consistent with DETF range for Stage III DES-like project
• Large uncertainties in systematics remain, but FoM is robust to uncertainties
in any one probe, and we haven’t made use of all the information
DES Status
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Low-risk, near-term (2011-16) project with high discovery potential
Survey strategy delivers substantial DE science after 2 years
Synergy with SPT and VISTA
Precursor to LSST, DUNE and JDEM
Total cost is relatively modest (~ $30M)
  STFC approved £1.7M for the DES optical corrector, subject to
funding in the US
  Glass ordered by UCL in Sep 07 (funds from 5 universities)
  DES in the US President budget request for FY08, FY09
  DOE CD1 approved; CD2/CD3a recommended in Jan 08
  NSF contribution to data management
The Dark Energy Survey
Camera: DECam
DECam will replace the prime focus cage
4m Blanco telescope
The Dark Energy Survey
“Evidence” for Dark Energy
Observational data
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Type Ia Supernovae
Galaxy Clusters
Cosmic Microwave Background
Large Scale Structure
Gravitational Lensing
Physical effects:
•  Geometry
•  Growth of Structure
Both depend on the Hubble expansion rate:
H2(z) = H20 [ΩM (1+z) 3 + ΩDE (1+z) 3 (1+w) ]
(flat)
DES+VISTA: Galaxy Power
Spectrum
For the same clipping
Banerji et al 0711.1059
threshold, we can measure the
power spectrum accurately to
higher redshifts using the DES
+VISTA data.
DES grizY
δP
1 
1 
∝
1 +

P
nP 
V 
dN
dV
= f sky
n( z )
dz
dz
nPgal = n( z )[ D ( z )]2 [b( z )]2 Pm ( k* )
DES grizY + VISTA JHK
Euclid (DUNE/Space) with and without NIR:
F.B. Abdalla, A. Amara, P. Capak, E.S. Cypriano,
OL, J. Rhodes (0705.1437v1)
Plots generated using JPL
mocks and ANNz
Wide Field Photometry
Survey
FOV Area
(deg2) (deg2)
1
172
start
CFHTLS
Diameter
(m)
3.6
KIDS (VST)
2.6
1
1700
2008
DES (NOAO)
4
2
5000
2009
HSC (Subaru)
8
2
2000?
2011
Pan-STARRS
1.8(x4)
7(× 4) 30000
2007(12)
LSST
8
7
2014
30000
cf. Multi-Object Spectroscopy:
VLT/VIMOS, WFMOS, JWST, BOSS, HET-DEX
2003
Newton, Principa (1687, Book I,
Proposition 77, Theorem 37)
Dark Energy Survey Science
Program
DES will use Four Probes of Dark Energy
–  Galaxy Clusters
•  Redshifts and masses of ~100,000 clusters to z>1
•  Of which ~10,000 will have SZE measurements from
SPT
•  Sensitive to growth of structure and geometry
–  Weak Lensing
•  Shape measurements of 300 million galaxies
•  Sensitive to growth of structure and geometry
–  Baryon Acoustic Oscillations
•  300 million galaxies to z = 1 and beyond
•  Sensitive to geometry
–  Supernovae
•  >9 sq deg SN Ia survey
•  1000-1400 SN Ia to z ~1
•  Sensitive to geometry
The four probes are complementary and will
provide insight into the systematic
uncertainties
Supernovae Ia
•  Geometric Probe of Dark Energy
SDSS
I. Galaxy Clusters
•  Galaxy cluster abundance, mass function,
and correlations sensitive to cosmology via
effects on volume and on growth rate of
perturbations
•  Complementary cluster samples
•  DES optical data provide accurate cluster
photometric redshifts
•  South Pole Telescope (SPT) SunyaevZel’dovich effect (SZE) data provides robust
cluster masses
•  Tens of thousands of clusters in 4000 deg2
area of DES-SPT overlap
•  Multiple cluster mass estimators (optical
richness, SZ, lensing) and cross-checks of
sample selection effects
from J. Mohr
II. Weak Lensing Tomography
• Cosmic Shear Angular
Power Spectrum in
Photo-z Slices
• Shapes of ~300 million
well-resolved galaxies,
〈z〉 = 0.7
• Primary Systematics:
photo-z’s,
PSF anisotropy,
shear calibration
Statistical errors
shown
• Extra info in bispectrum &
galaxy-shear: robust
DES WL
assume
0.9” 0.9”
PSF PSF
= median
delivered
to
DES
WL forecasts
forecastsconservatively
conservatively
assume
= median
delivered
to
existing
DES
shouldshould
do better
be more
stable
existingBlanco
Blancocamera:
camera:
DECam
do&better
& be
more stable
III. BAO and Galaxy Power Spectrum
Wiggles due
to BAO
Systematics:
photo-z’s,
correlated
photometric
errors, nonlinearity, scaledependent bias
Fosalba & Gaztanaga
Blake & Bridle
IV. Supernovae
•  Geometric Probe of Dark Energy
•  Baseline: use 10% of photometric
time, most of the non-photometric
time: 5 visits per lunation in riz
•  ~900-4000 well-measured SN Ia
lightcurves to z~1
•  Larger sample, improved z-band
response (fully depleted CCDs)
compared to ESSENCE, SNLS:
reduce dependence on rest-frame
u-band and Malmquist bias
DES Forecasts: Power of Multiple
Techniques
w(z) =w0+wa(1–a)
Assumptions:
Clusters:
σ8=0.75, zmax=1.5,
WL mass calibration
DETF Figure of
Merit: inverse
area of ellipse
BAO: lmax=300
WL: lmax=1000
Statistical+photo-z
systematic errors only
geometric+
growth
Spatial curvature, galaxy
bias marginalized,
Planck CMB prior
Stage II not
included here
Factor 4.6 relative to Stage II
geometric
The DES Instrument: DECam
•  To meet the DES science
requirements, within the allocated
time period DECam must have:
•  3 sq. deg. field of view
•  excellent image quality
•  red sensitive CCDs
•  g,r,i,z,Y filters
•  The DECam R&D program is
nearly complete
•  Final Design and Construction are
about to begin
DECam Focal Plane
62 2kx4k Image CCDs: 520 MPix
8 2kx2k Alignment/focus CCDs
4 2kx2k Guide CCDs
DECam Overview
•  CCD focal plane is housed in a
vacuum vessel (the imager) which is
supported by the barrel
•  CCD readout electronic crates are
mounted to the outside of the Imager
and are actively cooled.
•  Filter changer (8 filter capacity) and
shutter form one mechanical unit.
•  Hexapod provides focus and lateral
Optics
Attachment ring
Bipods
•  Five element fused silica
corrector
Focal plane
C5, vacuum
window
C4
•  Two aspheric surfaces
•  Last element is window of CCD
vessel
Filters &
Shutter
C2 - C3
•  Blanks
complete
Prototypeare
Cell and
Pad covers
•  Lenses being polished and
coated by SESO
C1
DECam CCDs
•  Red sensitive CCDs developed by
LBNL:
–  QE> 50% at 1000 nm
–  250 microns thick
–  2 RO channels/device
–  readout time ~17sec
•  Three stage fabrication:
–  Wafers fabricated at Dalsa
–  Final processing steps at LBNL
–  Packaging at Fermilab
•  20 out of the 60 2k x 4k CCDs
delivered to Fermilab are potential
science grade
DECam / Mosaic II QE comparison
100
90
80
70
60
QE, LBNL (%)
QE, SITe (%)
50
40
30
20
10
0
300
400
500
600
700
800
Wavelength (nm)
900
1000
1100
Multi-CCD Test Vessel / Imager
Prototype
•  10 prototype CCD
packages installed in
Multi-CCD Test
Vessel
•  Prototype high density
boards derived from
the NOAO Monsoon
system meet the
readout specifications
(<10 e noise @
250kpix/sec).