Transcript The Dark Energy Survey and The Dark Energy Spectrograph Josh Frieman DES Project Director Portsmouth, June 2011

The Dark Energy Survey
and
The Dark Energy
Spectrograph
Josh Frieman
DES Project Director
Portsmouth, June 2011
Massive Spectroscopy of DES Targets
Would enable (see today’s talks):
•Clusters: cluster spec. z’s and dynamical masses from
velocity dispersions: improve mass-observable calibration
•WL+RSD: DESpec Redshift Space Distortions plus DES WL:
powerful probe of DE and test of GR+DE vs Modified Gravity
•LSS: radial BAO: H(z), and improved DA(z)
•SNe, galaxy evolution: host-galaxy z’s and spectroscopic
typing (metallicities, stellar masses) to control systematics
•All: calibrate photo-z’s via angular cross-correlation?
•Local dwarf galaxies?: small-scale probes of gravity
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Josh Frieman, DESpec meeting
Portsmouth, June, 2011
Weak Lensing and Redshift Space Distortions
Gaztanaga, Eriksen, et al
• Constraints strongest if imaging and spectroscopy
cover same sky, as DES+DESpec will
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Josh Frieman, DESpec meeting
Portsmouth, June, 2011
Bernstein & Cai
Dark Energy Spectrograph: DESpec
• Upgrade of DES currently under study:
– multi-object prime focus spectrograph for the Blanco 4m,
interchangeable with DECam, 3.8 sq. deg. FOV
– λ=600-1000 nm with resolution R~3300 at 1000 nm
– Use DECam infrastructure (cage, barrel, hexapod, most
optics, shutter, 20 spare CCDs,…): substantial cost saving
– 10 low-cost spectrographs, 4000 robotically positioned fibers
– Redshifts for ~7 million DES galaxies (in ~270 nights), ~20
million from DES+LSST (~800 nights)
• Enhance Dark Energy science reach of DES by factor ~several,
especially testing DE vs. modified gravity: Stage IV DETF
• Enhance DE science reach of Stage IV LSST
• Uniquely synergize with DES and LSST: power of `same sky’
The Dark Energy Camera
• DECam mounted on
Telescope Simulator
at Fermilab
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Josh Frieman, DESpec meeting
Portsmouth, June, 2011
The Dark Energy Camera
• DECam mounted on
Telescope Simulator
at Fermilab
• To first
approximation,
DESpec would
interchange the
imager with a fiberpositioning system
that feeds multiple
spectrographs
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Josh Frieman, DESpec meeting
Portsmouth, June, 2011
DESpec Concept Optical Design
New
C6 C5
C4
New
ADC
C3
C2
C1
See talk by Steve Kent
Fiber Positioner Example
“Cobra”
• FP with “Cobras”,
“twirling posts” with
rotating fiber. Two
axes of rotation
Fiber
Patrol Radius
See talk by Richard Ellis
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Fiber Positioner Example
FMOS Echidna on the Subaru
• Operating fiber-positioner
on Subaru with ~400
fibers.
• Spines pivot from mounts
near the bases
• Naturally handles a
varying target density
because the tips are
small
See talk by Will Saunders
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Rationales for Blanco Spectroscopy
•Uniform, deep imaging catalogs from DES+VHS for targeting:
enable powerful new science beyond what redshifts alone
provide (e.g., WL+RSD)
•Maximally enhance science reach of DES: improve all the DE
methods+enable new methods (RSD, radial BAO)
•Hemispheric synergy with LSST: part of a broader eventual
strategy for LSST follow-up: extend to ~15,000 sq deg
•Excellent site: 0.65” seeing (0.9” Mosaic), high number of
useable nights (80%) yield fast (hence cheap) survey
•Lower cost & schedule risks by reusing/capitalizing on many
DECam components: optics, CCDs, cage, hexapod, shutter
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Josh Frieman, DESpec meeting
Portsmouth, June, 2011
Caveats
• NOAO does not currently have plans for an
Announcement of Opportunity for new instrument on the
Blanco following DECam.
• Future of NOAO facilities will depend on outcome of NSF
Astronomy Division Portfolio Review in 2011-2012.
•Need to further evaluate DESpec in the global context of
planned & proposed spectroscopic survey facilities (e.g.,
BigBOSS, Sumire, 4MOST,…): DESpec should
complement rather than compete with other projects where
possible.
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Josh Frieman, DESpec meeting
Portsmouth, June, 2011
DESpec and BigBOSS
• Both projects involve 4000-5000-fiber spectrographs on
~identical 4m telescopes, with related science goals.
• DE reach increases with survey area, so ideally would
survey both north (BB) and south (DESpec).
• Similar survey power (area/depth per unit time) for the two
concepts: BB larger FOV, DESpec higher fiber density.
• DESpec uniquely covers entire survey areas of DES and
LSST, maximizing synergistic science (WL+RSD).
• DESpec would reuse much of the DECam infrastructure,
resulting in cost savings.
Path Forward
•DESpec a natural “upgrade” to the science capability of DES.
Project could structurally follow the path blazed by DES:
international collaboration with DOE+NSF support in the US,
building on the successful DES collaboration, with opportunities
for new partners.
•Material above presented to Fermilab PAC last week, with very
favorable response.
•Revise and then release White Paper (1st draft exists) that lays
out the science case, reference survey strategy & reference
technical design motivated by science requirements.
•Next few months: optimize target selection for key DE probes,
confirm with more detailed simulations. Continue to elaborate
science case, carry out technical R&D, and build collaboration.
Aim for external review in the Fall. Data release policy?