1. Next generation redshift surveys with the ESO-VLT
Olivier Le Fèvre, Laboratoire d’Astrophysique de Marseille
Today
Instrumentation for surveys on the VLT
Several surveys covering up to z~6
Tomorrow ?
Need for massive surveys
Need for new instrumentation ?
Short term
Long term

2. Instrumentation for surveys at the VLT
Optical instruments
VIMOS-UT3: multi-slit 14x16 arcmin², 150 to 1000 slits (if 10arcsec long, R~220 to 2500)
FORS-UT2: multi-slit 7x7 arcmin², 100 slits max, red optimized
FLAMES:-UT4 multi-fiber, 130 fibers, 15 small IFUs
In dev.: MUSE (2011), 1 arcmin² IFU + adaptive optics
NIR instruments
Not really for surveys but for follow-ups
Missing a NIR-MOS
SINFONI: single object IFU cryogenic, JHK bands
ISAAC: long-slit cryogenic, JHK bands
In dev.: KMOS (2011), 24 IFUs, JHK bands

3. VIMOS -VLT-UT3
A highly efficient high redshift machine in operations since 2002 on the VLT

4. Multi-slit mode
Low res.
High res.

5. Instruments for surveys at the VLT
FLAMES=GIRAFFE+OzPoz
130 fibers, microns
FORS2, microns
7x7 arcmin², 100 slits

6. Instruments for follow-up from surveys
SINFONI
3D-IFU
1-2.5 microns
On-going: 150 VVDS galaxies 1<z<1.8

7. On-going redshift surveys at the VLT
Several surveys covering up to z~6
Wide and Deep [VIMOS]: VVDS aiming for up to 30deg² and 1.5x105 redshifts
Wide [VIMOS]: zCOSMOS (2 deg²)
Medium-deep [VIMOS, FORS2]: UDF (1 deg²)
Deep [VIMOS]:
GOODS, 7000 redshifts
zCOSMOS, 1.5<z<3, redshifts
Ultra-Deep: VVDS [VIMOS], GMASS [FORS2]
a few hundred sq.arcmin, a few thousand objects
Others
3D integral field: VVDS-SINFONI, FLAMES
Other programs…

8. VIMOS VLT Deep Survey R~230, 5500-9300Å ~50000 spectra today
Goal >20000 Deep and Wide

9. N(z): IAB22.5 , IAB24, IAB24.75
Magnitude selection only: complete census of the population, minimize apriori selection bias
IAB≤22.5, <z>=0.55
VVDS
redshift desert
IAB≤24
<z>=0.75
High redshift tail to z~4-5
22.5≤IAB≤24.75
<z>=1.4
High redshift tail to z~5
40% of galaxies with z>1.5

10. VVDS-Wide, 35000 redshifts 4 deg² Measuring  at z=0.8, using (rp,)
=0.7±0.24
From 8 deg² (Guzzo et al., submitted)
4 deg²

11. VVDS-UltraDeep Magnitude selected IAB≤24.75 Toward a complete census
No apriori
~50% of galaxies at z~3 are not LBGs
■ VVDS UDeep
LBG Box

12. Measuring galaxy evolution from the VVDS
Distribution in LSS
Luminosity / SFR / Mass evolution
High redshift populations
N(z)
Reddest Galaxies to z~2
Luminosity Function
Galaxy density field
1000 galaxies 1.4 < z < 5
Luminosity Density
Correlation function
SFR
1000 galaxies IAB≤24.75
Mass function
130 faint QSOs to z=5
Track evolution versus Environment, Luminosity, galaxy Type,…

13. 40+ papers published so far
VVDS results
Clustering
Stellar mass
MB=-17
MB=-21
Luminosity function to z~3
By type
Vs. environment
40+ papers published so far
Type density relation evol

14. zCOSMOS With VLT-VIMOS
Wide: 2 deg², spectra, IAB≤22.5, 0<z<1.2
Deep: 1 deg², spectra, BzK+UGR selected 1.5<z<3
zCOSMOS
On HST-COSMOS 2 deg² field
1.5<z<3
Combined spectra with Lya in emission vs; in absorption

15. On-going redshift surveys at the VLT: summary
At z~1 : ~10 deg², ~100Mpc scales, several 104 redshifts, coming up: ~105 redshifts
At z~2-3: ~1-2 deg², ~50Mpc scales, a few hundred redshifts now, several 103 redshifts coming up
At z=4-6: A few tens of redshifts
20-100 smaller at z~1 in dz=0.2 than 2dFGRS-SDSS
Keep in mind the huge human effort needed
Currently VVDS, zCOSMOS require 1week, 2 people for 500 spectra
automated z measurement when 0<z<5 is not yet achieved

16. Multi- photometry, visible + near-IR
Probing the Universe
with spectroscopic surveys
Understand galaxy formation and evolution
Measure Cosmology parameters
Understand LSS formation and evolution
Towards reionisation z~15
SNIa
Baryons oscillations
,8 …
Large scales, >100 Mpc
High redshifts z>~1-6
Very deep, M* at z~10
Small fields
Several thousand objets
Wide fields >10deg²
Deep, M* at z~3
>10^5 objects
Multi-object spectroscopy
NIR-MIR
3D spectroscopy
NIR-MIR
Multi-object spectroscopy
Multi- photometry, visible + near-IR
Lensing, CMB, SnIa…

17. Next surveys at the VLT: Test cases
“SDSS at z~1”:
106 galaxies, deg²
>200Mpc scales
AB~23
All-sky survey to z~1
A few 108 galaxies, deg²
“VVDS at z~3-6”
105 galaxies, 25deg²
Extremely deep probe z~10
A few hundred objects, AB~26

18. 1. VIMOS VLT Large Survey SDSS at z~1
“SDSS at z~1”: BAO++… (galaxies, clusters, QSOs)
7x106 galaxies, 100 deg²
>200Mpc scales
AB~22.5
100 deg²: 4800h with VIMOS
48 VIMOS pointings to cover 1deg²
45 min integrations for IAB≤22.5 (85% completeness) + overhead
Need 480 nights = 5 years 100n/y
CAN BE DONE TODAY !
Dedicate VLT-UT3+VIMOS

19. 2. ‘All-sky’ survey at z~1 Requirements:
10000 deg² (high galactic latitude)
z~0.5-1, IAB≤22.5
1 in 4 sampling
5-10 years survey
Need 1000y with VIMOS: need to think of new instrument !
Boost the multiplex gain

20. 2. ‘All-sky’ survey at z~1 Ground-based facility Space-based facility
Need ~104 simultanous redshifts in 1h to complete in 5-10y
2x108 redshifts
Concepts:
WFMOS: on 8m, 1.75deg² field, 4000 fibers, need ~800 nights
MEGAMOS: on the VLT, >1.5deg², spectra with micro-mirrors / shutters. Not easy: feasibility study
Space-based facility
Submitted to ESA ‘Cosmic-Vision’: SPACE mission
telescope 1.5m, 0.5deg field, spectra with micro-mirrors
Can do 0.5x109 redshifts in 3y mission, down to H=23 (15 min)

21. 3. VVDS-like at z=3-6 Requirements: With existing facilities
U, B, V and R-band Lyman-break and Ly- selection at IAB≤25
25 deg² to probe >100Mpc and beat cosmic variance
105 spectra for stats
With existing facilities
VIMOS:
need 20h integrations
4000h=500 nights program
Space-based facility
SPACE-like instrument: deep probe of several 105 z
CAN BE DONE TODAY !
Dedicate VLT-UT3+VIMOS

22. 4. Ultra-deep probe z=10 Requirements: With existing facilities
A few hundred objects
Field: guess, depends on the number density
With existing facilities
Not possible with 8m (?)
Need space (beat sky and thermal background)
Future facilities
ELT multi-slit and multi-IFU
SPACE-like instrument: telescope 1.5m, 0.5deg field, spectra with micro-mirrors
JWST

23. Next generation surveys with the VLT
Summary
Next generation surveys with the VLT
Dedicate VLT for very large redshift surveys
Motivate the community
Short term: dedicate VLT-VIMOS to a few large surveys
z~1, 106 redshifts
z~3-6, 105 redshifts
Long term: New instrument on 8m very wide field MOS with slits/fibers
Note: further develop automation of z measurement at high z. Not trivial