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VIMOS

VIMOS. Peter Hammersley phammers@eso.org & Marina Rejkuba mrejkuba@eso.org May 25 th , 2012. What is VIMOS. Visible Imager / multi slit / IFU spectrometer D esigned to measure large numbers of redshifts

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VIMOS

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  1. VIMOS Peter Hammersley phammers@eso.org & Marina Rejkuba mrejkuba@eso.org May 25th, 2012

  2. What is VIMOS • Visible Imager / multi slit / IFU spectrometer • Designed to measure large numbers of redshifts • Cover as large a field as possible • Built by a French / Italian consortium PI: O. Le Fevre • Delivered to Paranal 2001 • Mounted on UT3

  3. VIMOS is 4 Instruments joined together

  4. The Instrument II

  5. The Capabilities : Imaging • UBVRIz imaging • 4 fields each 7x8 arc mins • Plate scale 0.205“ per pixel • 2K x2.4K pixels used

  6. The Capabilities : MOS Invar masks 6 GRISMS • HR-Red , HR-Orange & HR-Blue R = 2200 max 200 x8” slits • MR R= 1000 max 200 x8” slits • LR -red & LR-blue R= 200 max 800 x8” slits

  7. The Capabilities : IFU 6400 fibres Field 54”x54’’, 27”x27’’ or 13”x13” • Depends on resolution and plate scale: 0.66’’ or 0.33’’ per fibre

  8. The VIMOS upgrade Motivation: The ESO large scale spectroscopic surveys • Replace worn-out components (e.g. shutters) • Reduce flexure • Improve focus control • Improve image quality and sensitivity • Replace detectors & HR-blue grisms • Improve reliability • Reduce overheads (PILMOS) • Improve the pipeline

  9. Changing the detector: I band Imaging and improved sensitivity Before After

  10. Fringing at the CaII triplet

  11. Publications • 358 papers published so far with VIMOS data • Close to 60 papers/year • Most productive instrument after the first instruments (UVES, FORS1, FORS2, and ISAAC)

  12. Which kind of science? • The first VIMOS paper: O. Hainaut et al. , 2004: “Post-perihelion observations of comet 1P/Halley. V: rh = 28.1 AU” • The most recent papers: • “Two-dimensional kinematics of SLACS lenses - IV. The complete VLT-VIMOS data set” by Czoske et al. • “Variability and stellar populations with deep optical-IR images of the Milky Way disc: matching VVV with VLT/VIMOS data” by Pietrukowicz et al. • “A VIMOS spectroscopy study of photometric variables and straggler candidates in ω Centauri” by Rozyczka et al. • “New Constraints on the Evolution of the Stellar-to-dark Matter Connection: A Combined Analysis of Galaxy-Galaxy Lensing, Clustering, and Stellar Mass Functions from z = 0.2 to z =1” by Leauthaud et al.

  13. Redshift machine Le Fevre et al. (VVDS) M. Tanaka et al. 2009 (ESO PR)

  14. VIMOS first light images

  15. Oversubscription vs. undersubscription • Large Programmes on VIMOS are all targeting cosmological fields at RA~2h, 3h, 10h, 22h • VVDS • VIPERS • zCOSMOS • GOODS • ULIRGs survey • High-z clusters survey • Instrument is under-used at RA~5-8h, 15-19h

  16. Some tips for observers • Pre-imaging is mandatory, but PILMOS coming • No atmospheric dispersion corrector & fixed mask/slit orientation: observe within +/- 2h from meridian  limited visibility and observability • Fast preparation of MOS follow-up observations (VMMPS) • Attached night-time calibrations • LARGE overheads • Spectrophotometry? • IFU: fibre fringing – check Carina’s paper (Lagerholm et al. 2012) • IFU: think about the sky subtraction for extended objects • IMG + MOS: affected by vignetting from IFU

  17. Vignettingdue to IFU

  18. Pipeline • All observing modes (IMG, MOS, IFU) • Improvements with the latest release • Spectra are identified via pattern matching • Wavelength calibration from lamp spectra + second order corrections using sky lines • Still missing combination of dithered exposures

  19. Highlights • Largest optical IFU on an 8m class telescope • The only wide field imager available to ESO community • Highest multiplex and high efficiency (slits) redshift machine • Very productive on a variety of scientific topics • Highly requested but sometimes undersubscribed

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