Transcript Slide 1

WIDE FIELD MULTI-OBJECT SPECTROSCOPY
To cede or not to cede………
Keck at disadvantage for ultra-wide field of view science due
to f/15 secondary and difficulty of locating instrumentation at
PF (no corrector)
There may be avenues to highly-multiplexed wide field
spectroscopy for the Keck community:
WFMOS - community access through time trades?
DEIMOS - double the footprint and/or increase blue
sensitivity?
MOBIE - TMT instrument adaptable to Keck?
Why should we consider them?
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The Imaging Bubble
Numerous imaging surveys ongoing or coming online in the next ~ 5 - 10 years
SuprimeCam (Subaru) d~0.5 deg (HyperSuprimeCam d~1.5 deg)
Megacam (CFHT) ~ 1 x 1 deg Legacy Survey
MOSAIC/DES (KPNO/CTIO) ~0.5 x 0.5 deg
SEGUE/SDSS (III)
LSST
UKIDSS (UKIRT)
VISTA (ESO)
PanSTARRS
ODI (WIYN)
WISE
And many more!
Who will follow up these “fire hoses” of data?
Keck can observe +20 to - 30 degrees -> substantial overlap with LSST
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Science Drivers
•Dark Energy
•Cosmology - near and far field
•Galactic Archeology
•Galaxy Assembly - hierarchical structure
•Dark Matter
DEIMOS Masks tiled on 42’ x 28’ CFHT pointing
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Science Drivers
all FOV limited
• Chemo-dynamic structure of galactic components (stars and star clusters):
- interfaces between disk/bulge/halo
- ancient dissolved and surviving substructures (victims of smallest
building blocks)
• Fossil record of chemical evolution of stellar populations
- chemical signature of ancient accretions
- discovery and properties of metal poor Pop III stars
• Evolutionary history of stellar components
- tagging the chemical evolution
• Formation and evolution of galaxies
-linking components to high redshift universe
• Detailed dynamics of globular clusters and surviving satellites
- tracing role, nature and distribution of DM
• Baryonic Acoustic Oscillations (BAO)
- aim to constrain w to 3% (best test of w ¹ -1.0)
• Redshift Space Distortions (RSD)
- seek g to 1.5% (first test of modified GR as soln to DE)
• Density growth and modified gravity
• Redshift Surveys
- large scale structure and galaxy evolution in galaxy clusters and field
And many more!
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Positioner and Source Allocation
Subsection of Instrument Focal Plane
Patrol Region
Fiber Tip
Edge of Field of View
.
Source
Overlapping Patrol Regions
Fiber Tips that cannot reach a
source
Fiber Tips that can reach a
source
Unallocated sources
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Current Status of WFMOS
• Gemini selected JPL/Caltech design (PI Richard Ellis) over
AAO/JHU proposal, but then abandoned WFMOS entirely
• Gemini funded a useful design study which forms the basis
of a new way forward
Japanese community remains enthusiastic and full funding
awarded this month from Japanese stimulus package Japanese PI Hitoshi Murayama – Director IPMU
New government - implications unclear
Implications for Keck Strategic Plan
• WFMOS covers unique science; Europe is anxiously examining what
to do and already touching the waters (FLAMES, VIPERS..); Keck
has to decide its strategy
• If Japanese funding comes through, WFMOS will become an unique
facility outperforming any equivalent instrument on VLT, Magellan or
Keck (current or planned). ETA 2014
• Wide field spectroscopy on Subaru has unique aspects: shared
imager, robust telescope, heritage of wide field science
• Japan will join TMT on Mauna Kea (modulo new government policy
changes)
• Wise approach is for Keck to complement WFMOS and organize
partnerships and trades (“join not compete”) e.g. DEIMOS
• If Japanese funding fails to materialize, indications are that original
partners will try to raise funds; this may open new possibilities (e.g.
joint fund-raising)
• Planning a fiber-fed facility on Keck should not be a priority at the
moment (~$60M project on Subaru)
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DEIMOS
Bigger and Bluer
Original Instrument
M. Davis (PI, UCB),
S. Faber (Co-PI, UCSC)
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Goals vs. Performance
DEIMOS was conceived to be maximally
efficient for faint-object spectroscopy of
objects densely packed on sky
• Minimize the effect of sky background
– “Get between” OH lines: =1.25 A, R = 6000 ,
x4 speed gain
– Accurate flat-fielding: 0.2% rms (photon-limited
for 10-hr exposures)
– Stable image position (fringing): 0.6 px rms
(achieved?)
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Goals vs. Performance
• High observing efficiency
– Long slit length on sky: 16.7’, >130 slitlets
– Broad spectral coverage: 2000 resolution elements
– High throughput: 28% peak (with atm & tel; 50%
DEIMOS alone)
– Low readout noise: 2.3 e–
– Fast readout time: 56 sec
– Rapid slitmask alignment: 5 min
• Excellent image quality (3800 A to 10,500 A)
– Hoped for:
– Actual:
0.6-0.8 px (1-d rms with 15 pixels)
0.8-1.2 px => ~2.0-2.8 px FWHM
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Considerations
Many/most applications with DEIMOS overfill the current
FOV so will double the efficiency with twice the footprint
For some applications (e.g., DE/BAO) ultra-large FOV
crucial
Blue sensitivity allows stellar populations studies
simultaneously with velocity/redshift work
Needs good throughput down to 4000 A for abundances,
metallicities, alpha-enhancements
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Stacked spectra of 50 galaxies at z ~ 0.8
<z> = 0.78
M67 is a local star cluster
with age 4 Byr
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Current Blue Throughput
QuickTime™ and a
decompressor
are needed to see this picture.
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Considerations II
Deserts
- few diagnostic lines in the 6500 - 8000 A range
- redshift desert used to be z = 1(where oxygen leaves
the spectrum)
to 2.5 (where Lyman  enters spectrum)
LRIS-B helped by opening up the blue side
but has 5.7 x 7.2 arcmin ~40 sq arcmin) FOV
DEIMOS is 80 sq arcmin, so doubling DEIMOS footprint
quadruples area accessed by LRIS.
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Considerations III
WFMOS
Synergy with GAIA: LR to V=20, HR to V=17
• Low Res (R~1000 - 5000) vels to 2-3 km/s; [Fe/H] to 0.1-0.2 dex; [Mg/Fe]
• High Res (R~20,000) vels to 0.5 km/s; EWs to 5mA; λλ 4800 – 6800A
abundances
DEIMOS lower multiplexing factor and smaller FOV but fainter capability
WFMOS and DEIMOS are complementary
But what about MOBIE vs. DEIMOS?
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DEIMOS Camera Challenges
3 steep
aspherics
CaF2
Thermal
compensator
All assembly
tolerances =
0.001 inch
14 in diam
Fluid
couplings
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Options
DEIMOS - twice footprint no change in blue performance
DEIMOS - twice footprint, blue sensitivity to 4000A 
DEIMOS - make a dedicated blue side with sensitivity to 3200A
Modify MOBIE for Keck? - next talk
Time trade with Subaru for ultra-wide field apps
Do nothing and cede our historic lead X
Cost/benefit/feasibility studies needed
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