The Dark Energy Survey

1

• The Dark Energy Survey
• J. Frieman, M. Becker, J. Carlstrom, M. Gladders,
  W. Hu, R. Kessler, B. Koester, A. Kravtsov, for
  the DES Collaboration

Overview
Probing Dark Energy
Forecast Constraints
The Dark Energy Survey (DES) is a 5-year, 5000
sq. deg. optical imaging survey in grizY bands
that will use a new mosaic CCD camera with 520
megapixels covering a 3 sq. deg. field of view on
the Blanco 4m telescope at the Cerro Tololo
Inter-American Observatory (CTIO). DES will
observe about 300 million galaxies and probe the
nature of the dark energy using four
complementary methods (i) the abundance and
clustering of galaxy clusters, in concert with
the South Pole Telescope Sunyaev-Zeldovich (SZ)
survey, (ii) weak gravitational lensing
tomography, (iii) baryon acoustic oscillations
via galaxy angular correlations, and (iv) Type Ia
supernova distances from repeat imaging of a
smaller area. Combining results from the
different methods will provide tighter
cosmological constraints comparing results from
the different methods will provide important
cross-checks on systematic errors. The processed
DES data will provide a long-term resource for
the astronomy community, and the Dark Energy
Camera will be available for general purpose
observing on the Blanco telescope.
Three views of Galaxy Clusters Left SDSS
optical image of a distant cluster DES will
detect many tens of thousands of clusters to
redshift z1.3 as concentrations of red galaxies
Center Weak lensing reconstructed mass map
(contours) superimposed on optical image of a
low-redshift cluster using data from the Blanco
4m (Joffre et al. 2000) DES will provide
statistical calibration of cluster masses via
weak lensing Right Dark matter distribution in
a cosmological simulation of a cluster-size halo
simulations indicate a robust and tight scaling
relation between cluster mass and integrated SZ
flux.
w(z) w0wa(1a)
Forecast DES constraints (griz data only) on dark
energy equation of state parameters w0 and wa.
Spatial curvature has been marginalized over and
a Planck CMB prior assumed. Photometric redshift
systematic error nuisance parameters also
marginalized (see below). Table shows
marginalized constraints and the Dark Energy Task
Force Figure of Merit, proportional to the
inverse area of the constraint ellipses above.
Stage II denotes dark energy constraints
expected from on-going projects.
Clockwise from top left 1. N-body simulation of
large-scale structure covering the DES
footprint 2. Blanco 4m dome with Magellanic
clouds and Milky Way overhead 3. Blanco
telescope with prime focus cage at top 4. layout
of Dark Energy Camera, showing corrector optics
and new prime focus cage 5. Multi-CCD test
vessel in U. Chicago machine shop 6. DECam focal
plane layout with 62 2kx4k CCDs 7. CCD wafer
the fully depleted, thick CCDs provide superior
quantum efficiency in the red passbands,
important for observations at z ?1.
Photometric Redshifts
Sensitivity to Dark Energy Upper left panel
predicted number of detected clusters vs.
redshift in SPTDES for dark energy equation of
state parameter w0 ?1 solid curves, with
power spectrum normalization ?80.75 (black) and
0.9 (blue) and w0 ?0.8 (dotted), with
statistical errors shown Upper right panel
baryon acoustic oscillation signal in galaxy
angular power spectrum in four redshift slices (z
0.3, 0.7, 1.1, 1.5) with varying w0 Lower
panel weak lensing cosmic shear angular power
spectrum in four redshift slices, for w0 ?1
(black) and ?0.9 (red), with binned statistical
errors shown only modes with multipole l lt 1000
(excluding grey region) are included in the
forecasts shown in next column.
Multi-band imaging enables approximate galaxy
redshift estimates based on observed colors Left
panel early-type galaxy spectra at redshifts z
0, 0.7, 1.4 overlaid on griz filter response
curves Right panel estimated photometric
redshift vs. true redshift for simulated DES
galaxy survey, including DES grizY and JHK
near-infrared imaging from the planned Vista
Hemisphere Survey at ESO. Photo-z error
distributions, critical for precise dark energy
constraints, will be well measured using existing
deep spectroscopic data.