WIDE FIELD MULTI-OBJECT SPECTROSCOPY

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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 SurveyMOSAIC/DES (KPNO/CTIO) ~0.5 x 0.5 degSEGUE/SDSS (III)LSST UKIDSS (UKIRT)VISTA (ESO)PanSTARRSODI (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 Driversall 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 fieldAnd many more!

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Positioner and Source Allocation

Subsection of Instrument Focal Plane

Edge of Field of View

Overlapping Patrol Regions

Fiber Tips that cannot reach a source

Fiber Tips that can reach a source

Unallocated sources

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Patrol Region

Fiber Tip

Source

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

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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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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?)

Goals vs. Performance

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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: 0.6-0.8 px (1-d rms with 15 pixels)– Actual: 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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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.

Considerations II

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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?

Considerations III

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DEIMOS Camera Challenges

14 in diam

Thermal compensator

CaF23 steep aspherics

Fluid couplings

All assembly tolerances = 0.001 inch

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Options

DEIMOS - twice footprint no change in blue performanceDEIMOS - 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