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WIDE FIELD MULTI-OBJECT SPECTROSCOPY

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)

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WIDE FIELD MULTI-OBJECT SPECTROSCOPY

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  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?

  2. 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

  3. 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

  4. 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 field And many more!

  5. 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

  6. 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

  7. 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)

  8. DEIMOS Bigger and Bluer Original Instrument M. Davis (PI, UCB), S. Faber (Co-PI, UCSC)

  9. 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?)

  10. 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

  11. 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

  12. M67 is a local star cluster with age 4 Byr Stacked spectra of 50 galaxies at z ~ 0.8 <z> = 0.78

  13. Current Blue Throughput

  14. 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.

  15. 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?

  16. 3 steep aspherics CaF2 Thermal compensator Fluid couplings 14 in diam DEIMOS Camera Challenges All assembly tolerances = 0.001 inch

  17. 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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