VIMOS

Peter Hammersleyphammers@eso.org

&Marina Rejkubamrejkuba@eso.org

May 25th, 2012

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

VIMOS is 4 Instruments joined together

The Instrument II

The Capabilities : Imaging

• UBVRIz imaging

• 4 fields each 7x8 arc mins

• Plate scale 0.205“ per pixel

• 2K x2.4K pixels used

The Capabilities : MOSInvar 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

The Capabilities : IFU6400 fibres

Field 54”x54’’, 27”x27’’ or 13”x13”- Depends on resolution and plate scale: 0.66’’ or 0.33’’ per fibre

The VIMOS upgradeMotivation: 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

Changing the detector: I band Imaging and improved sensitivity

Before

After

Fringing at the CaII triplet

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)

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.

Redshift machine

M. Tanaka et al. 2009 (ESO PR)

Le Fevre et al. (VVDS)

VIMOS first light images

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

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

Vignetting due to IFU

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

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