1. Ultra-Deep galaxy surveys with DIORAMAS@EELT the early build-up of galaxies Olivier Le Fèvre With the DIORAMAS team (F, IT, CH, SP)

2. Galaxy populations at and after reionisation What do we need ? – Find the “first” galaxies: exciting ! Journal headlines ! – Study the population of galaxies as it quickly evolves: astrophysics ! Requires large surveys – Search for objects and then study them – Several time steps, types, environment: need thousands of objects Surveys are more than ever the backbone of exploration – Statistical robustness

3. Understanding galaxy formation and evolution requires multi-step surveys A several step process 1.Search for objects: need to find objects before doing physics ! 2.Estimate the mean properties: N(z), luminosity, gas/stellar masses, SFRD, morphology, clustering, …. assemble representative samples 3.Isolate well defined sub-populations for detailed studies, e.g. kinematics 4.Infer a scenario & compare to models / simulations Deep multi-band imaging Large multiplex MOS IFU, AO-imaging, high-res spectra… Followed by all major surveys: CFRS, DEEP2, VVDS/MASSIV, IMAGES, LBG/SINS, zCOSMOS… Instrument flow

4. Galaxy redshift surveys What is to be expected when EELT starts ? z<2 “all sky” coverage from EUCLID: 50 million spectroscopic redshifts 2<z6 will still be under-explored: ~20 sq.deg ~50000 z spec Not enough for a comprehensive picture 6<z<10+: HST then JWST starting 2018 ~1 sq.deg 1000 z spec ? Not enough for robust statistics Not enough for well defined case studies

5. Finding first light objects z>6.5 What are we looking for ? Very faint objects AB>26.5 Relatively sparse: 0.1 to 1 object per arcmin² per Δz=1 The IGM will cut their observed flux below Ly  – Main signatures: Ly  -dropout and Ly  emission Need to sample from very rare bright objects to more numerous small building bricks (still rare on the plane of the sky) At z>6.5 all the information is in the NIR Careful: Take predictions on number density with caution (see historical perspective) Expect the unexpected… Keep a large parameter space for instruments

6. MOS(s) on the VLT MOS: a fundamental leap forward in instrumentation All major telescopes have one or more MOS VLT: 5-6 MOS flavors To cover a consistent parameter (discovery) space we need at least 2 of these, ideally combining modes, on the EELT MOSField RMultiplex FORS50 arcmin² 3300Å-1  m <3000100 FLAMES/GIRAFFE450 arcmin² 3600Å-1  m 7000-25000<130 VIMOS225 arcmin² 3600Å-1  250-2500~800 KMOS45 arcmin² 0.6-2.5  m 1800-420024 UVES/FLAMES450 arcmin² 3000-1  m ~1000008 (MUSE)1 arcmin² 0.48-0.93  m 1500-3000Wide field IFU: many objects per field

7. 2 imaging-multi-slit MOS in the top 3 @VLT Demonstrates « work-horse » versatile use – Galactic and Extra-Galactic Science VLT science output is dominated by MOS ! FORS2 VIMOS

8. Multi-band imaging Positions, magnitudes, shapes Select the sample Magnitudes, colors, NB... Multi-slit Spectroscopy Spectral features Redshift The best performances High sky subtraction accuracy 0.1% Main target, z=1.02 Serendipitous Lyman  z=4.3 Power of imaging-MOS

9. led to DIORAMAS instrument concept – phase A study High multiplex MOS with slits Imaging mode Use EELT natural seeing or GLAO-corrected beam – Instrument concept accomodates both Wide field: 6.8x6.8 arcmin² 0.37-1.6 microns ADC GLAO Natural Seeing ImagingMulti-slit VISx2NIRx2VISx2 NIRx2 A versatile instrument

10. DIORAMAS Opto-mechanical layout

11. ItemDesign value Spectral range[0.37 µm, 1.6 µm] Field of view6.78 x 6.78 arcmin² Slit sizeAny width/length: mean 0.5 arcsec, min.: 0.1 arcsec Pixel scale and sampling0.05 arcsec per pixel MOS multiplex 480 slits of 5 arcsec length at R~300 160 slits of 5 arcsec length at R~2000-3000 Spectral resolutionR~300 to 2700 for visible; R~400 to 3000 for NIR Limiting magnitude (4h): AB~29 in imaging, AB~26.5 in MOS High throughput: 30% VIS, 45% NIR (with detector) Excellent image quality: 150 mas 80% encircled energy DIORAMAS design parameters Gain @1µm 10-25  compared to JWST-NIRSPEC: x5 multiplex, x2.5-5 FOV, at equivalent depth/unit time

12. Wide field, multi-mode 12 VIS NIR JWST-NIRCAM Multi-slit R~300 High multiplex 480 slits Imaging JWST-NIRSPEC >30,000 sources in 7’x7’ to r AB =29.8 giJ

13. Wide field, multi-mode 13 VIS NIR JWST-NIRCAM Multi-slit R~3000 High multiplex: 160 slits Imaging JWST-NIRSPEC >30,000 sources in 7’x7’ to r AB =29.8 giJ

14. MOS spectroscopy at the EELT “ extragalactic” science Record holder Rare objects Population studies: sub-samples Large and deep spectroscopic surveys Large and deep imaging surveys Imaging-MOS DIORAMAS 3D IFU-MOS Need 2 MOS flavors A powerful combination for high-z: Imaging-MOS and multi-IFU+AO