The Dark Energy Survey Science

1
The Dark Energy Survey Science Elizabeth
Buckley-Geer, Fermilab
9/21/2007
The Blanco _at_ CTIO
DES Collaboration Fermilab, U of Illinois at
Urbana-Champaign, U of Chicago, LBNL, U of
Michigan, U of Pennsylvania, The Ohio State
University, Argonne National Laboratory
NOAO/CTIO, CSIC/Institut dEstudis Espacials de
Catalunya (Barcelona), Institut de Fisica DAltes
Energies (Barcelona), CIEMAT (Madrid), University
College London, U of Cambridge, U of Edinburgh, U
of Portsmouth, U of Sussex, Observatorio
Nacional, Centro Brasileiro de Pesquisas Fisicas,
Universidade Federal do Rio de Janeiro,
Universidade Federal do Rio Grande do Sul.

• The Question
• The expansion rate of the Universe appears to be
  accelerating. Is it that
• Universe is dominated by some particle or field
  (dark energy) that has negative pressure wP/r
  lt-1/3 or
• There exists a cosmological constant so that w-1
  or
• General Relativity or the Standard Model of
  Cosmology is incorrect.

Photometric Measurements of Galaxy Redshifts
The Survey 525 nights covering 5000 sq-deg in
g,r,i,z and Y band filters 9 sq-deg repeating SN
search
Overlap with SDSS Stripe 82 for redshift and
photometric calibration (200 sq deg)
DES Combines Four Probes of Dark Energy
Plot does not include DETF Stage II constraints
Connector region (800 sq deg)
68 CL constraints
Use g,r,i,z and Y band filters to track the 4000
Å break dz0.02 for galaxy clusters with redshift
z up to 1.3
Overlap with South Pole Telescope SZ Galaxy
Cluster Survey (4000 sq deg)
Assumptions (current WMAP constraints) Matter
Density ?mh20.14 Dark Energy Density
?DE0.73 Matter power spectrum amplitude
s80.75 ?0 -1 wa 0 Baryon density
?bh20.024 Spectral index ns 1 Spatial
curvature ?k 0 Plank prior for CMB

• 3) Type 1a Supernovae
• Type 1A Supernovae are standard candles.
• Luminosity vs redshift provides measurement of
  geometry of Universe
• DES will measure 1400 with zlt1.2

• 1) Weak Gravitational Lensing
• Measuring the apparent shapes of 300M source
  galaxies provides a direct measurement of the
  distribution of mass in between the source galaxy
  and the lens
• A statistical measure of 1 distortion
• The radial distances depend on the geometry of
  the Universe and the foreground matter
  distribution depends on the growth rate of mass
  structures.
• Provides a technique for calibrating the mass of
  lensing galaxies

DETF Figure of Merit 4.6

• 2) Galaxy Cluster Counts
• Measure 170K galaxy clusters to z 1.5 (20K
  clusters with have SZE flux measurement from SPT)
• Redshift from Photo-z
• Sensitive to growth of structure and to geometry
  of the Universe
• Primary uncertainty is bias and scatter of
  cluster mass vs observable relation

• 4) Baryon Acoustic Oscillations
• A characteristic angular scale is set by sound
  speed at t 370Ky when the relativistic plasma
  recombines

Angular Power Spectrum of Cosmic Shear
What we see
DES Simulation
1.0ltzlt1.5
0.5ltzlt1.0
Wiggles are due to BAO
Whats Going On
0ltzlt0.5

• Other Complementary Observations
• South Pole Telescope, a 4000 sq-deg SZ survey
  which started taking data in 2007
• SZ effect provides independent measurement of
  mass of 20,000 clusters
• Hot gas in clusters Compton scatters CMB photons
• Nearly independent of redshift (doesnt measure
  that).
• Vista Hemisphere Survey (5000 sq-deg)
• J K bands
• Reduces photo-z uncertainties by extending
  further into infrared.

• DES plans to answer
• Is Dark Energy the cosmological constant?
• If w -1 and dw/da 0, probably
• Otherwise, seek another model.
• Is Dark Energy a modification to gravity?
• Yes, if the growth of structure and geometric
  methods disagree.

Dark Energy Survey Is low-risk, near-term project
with a unique international position to synergize
with SPT and VISTA on the DETF Stage III
timescale.