SCIENCE GOALS OF EXTREMELY LARGE TELESCOPES

Sandro D’Odorico

European Southern Observatory

RENCONTRES DE MORIOND

Contents and Structures of the Universe La Thuile, Val d’Aosta, Italy; March 18-25, 2006

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TELESCOPE GROWTH SINCE GALILEO

Telescope size driven by glas technology for primary surface: (lenses-->monolithic mirrors segmented mirrors)

Today, advances in fabrication and control technologies allow EL segmented primary mirrors to be built for affordable costs and with competitive schedules

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RAPID GROWTH OF GROUND-BASED ASTRONOMY IN LITTLE MORE THAN A GENERATION

USA and European Astronomers surveying sites for 4m telescopes on Atacama Cerro Morado, Chile,

~1962 (ESO archive photo)

LaSilla Obs

VLT Obs

ALMA- a joint ESO-USA project, under construction

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THREE ELTs PROJECTS PRESENTLY UNDERGOING CONCEPTUAL –PHASE A STUDIES:

TMT ( Caltech, Univ. California, AURA, CANADA) 30m

European ELT 30-60m

Giant Magellan Telescope (Carnegie+ USA Univ.) 7x8m

TMTEuropean ELT

GMTProjected cost : 500 – 700 Million EUROS (~ x 1.15 $)

Start of operation: 2016

JWST

JWST: NIR and Thermal IR cameras and spectrographs

ALMA : antenna array for high angularresolution submillimeter observations

CONTEXT IN THE 2ND DECADE OF THE 3RD MILLENNIUM:

ELTs WILL WORK IN SINERGY WITH THE OTHER TWO MAJOR MULTI-SCOPE FACILITIES OF THAT DECADE, ALMA and JWST

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Northern Hemisphere

ACTUAL COLLECTING AREA OF LARGE TELESCOPES

Southern Hemisphere

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GAIN FROM AN ELT – OBSERVING REGIMES More photons from the larger collecting area ( fainter sources

within reach, higher S/N ratios for brightest sources)

For photon-noise dominated observations, the S/N gain proportional to D at fixed time and flux, the speed (1/ time required to reach given S/N ) to D2 ).

For sky limited observations of point-like sources at natural seeing (0.7 at V, 0.4” FWHM at K), the S/N proportional to D , the speed to D 2.

Higher angular resolution ( = 1.22 / D ) if atmospheric turbulence can be properly corrected with Adaptive Optics putting a significant fraction of the flux of point-like sources within the Airy disk

For sky limited observations of point-like, diffraction limited sources the S/N is proportional to D2, the speed to D 4 .

Point-like: stars in the Galaxy and in nearby galaxies, SN, GRB

Extended: even at the highest z, galaxies up to a few tens of arcsec in size

All of the above provided that instruments at least as efficient as those at 10m class telescopes can be built

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GAIN FROM AN ELT –THE ROLE OF ADAPTIVE OPTICS

To fully realize the ELT advantage the telescopes must be equipped with efficient AO system-s ahead of the instruments.

The AO system will consist of an array of artificial laser stars, of a number of wavefront sensors for the laser stars and natural stars in the field, 1-2 fast adaptive mirrors in the telescope optical train and/or in a separate system

Current performance predictions from extrapolation of various flavors of AOs being tested at 8-10m telescopes:

- on small, central field (< 30”) very good correction at NIR and thermal IR

- on selected regions of large fields (10’) moderate correction in NIR

- at visual- red wavelengths on axis and on large fields natural seeing improvement through correction of the Ground Layer of the atmosphere

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PRIMARY SCIENCE CASES FOR THE ELTs From the original science drivers - now filtered through the instrument concept

studies (OWL, TMT, ELT)

Mostly similar for the different projects, a few differences. With minimal personal bias

1. Detection and Characterization of Giant to Terrestrial Mass Planets

2. Stellar Populations in external galaxies up to Virgo as tracers of the star formation history though the life of the universe

3. Accurate redshift and characterization of SN up to redshift ~2

4. Detailed properties of galaxies and IGM 1 < z < 5 (mass, metallicity, luminosity function, SFR, extinction, tomography and metal content of IGM)

5. Redshift and characterization of galaxies up to z ~10 (reionisation?), GRBs to the same z as probes of IGM

6. Direct measurement of the expansion history of the Universe (E-ELT science case only)

7. Test of the variability of fundamental constants

………………………..

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INSTRUMENTS CONCEPTS MOST RELEVANT FOR COSMOLOGY-RELATED STUDIES (TMT, E-ELT)

SINGLE OR MULTI INTEGRAL FIELDS, NIR SPECTROGRAPH

Science Cases: 3, 4, 5

Requirements: ~5”x5”, 20mas sampling [ single field]; ~20 IFU 2” x 2” over 5’ x 5’ field / Z, J, H, K bands/ R=1000-4000 / throughput (including telescope) > 15%/ limiting magnitude Ks 23-24 in a few hours integration at S/N=10

AO requirements: EE 30-60 % within 50 mas at H. Via LTAO for the single field, via MOAO for large field

Flavors: IRIS, IRMOS at TMT, WSPEC, MOMSI at E-ELT

Challenges: AO performance over large field/ positionable, cryogenic IFU s

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INSTRUMENTS CONCEPTS MOST RELEVANT FOR COSMOLOGY-RELATED STUDIES (TMT, E-ELT)

MULTI OBJECT VISIBLE SPECTROGRAPHScience Cases: 4, mapping of dark halos in ellipticals from GC and PNRequirements: Field>40 sqmin, Spectral range : 310-1000 nm, Resolution = 500-5000/ Throughput >25% including telescopeAO requirements: Improvement of seeing median value by 20-30% with GLAOFlavors: WFOS at TMT, WSPEC at E-ELT (?)Challenges: Size and cost of instrument, performance of GLAO over large field, UV coverage

HIGH RESOLUTION OPTICAL SPECTROGRAPH Science Cases: 4,5, 6, 7Requirements: R= 20000-150000, throughput >15% including telescope,AO requirements: Seeing median improvement by GLAO desiderableFlavors: HROS at TMT, CODEX at E-ELTChallenges: Size of instrument and instrument components, cost, schedule, long-term calibration

Nr of QSO from SDSS observable in 3hrs at high resolution, for different S/N, as function of telescope diameter (credit TMT MTHR study)

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CODEX ( Cosmic Dynamics Experiment ): an instrument for High Resolution Spectroscopy at the ELTs

Legacy Science Program: To test the cosmological model by measuring the predicted drift in the redshift of distant sources as a function of time (Sandage ,1962)

Science Case and Instrument Concept Study carried out by ESO, IoA Cambridge, Obs.Geneve and INAF Trieste ( Pasquini et al . 2005)

Magnitude of the effect:

H0= 70 km/s/Mpc

t = 10 yr; at z=4 = 1 x 10 -6 A

v ~ 5 cm/s

redshift

)( )1( 0 etHHzdt

dzz

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CODEX : Cosmic Dynamics Experiment

The idea and the targets:To use ELT huge collecting area and an high resolution spectrograph with a highly accurate and stable wavelength scale to measure from high S/N spectra the shifts in the Ly forest and metal systems in the direction of bright QSOs over a large time interval (>10 years).

Capitalizing and expanding the expertise and methodology acquired with the successful spectroscopic planet searches (HARPS) and Ly forest studies with UVES at the VLT.

The Instrument: High Resolution Spectrograph operating in the spectral range:400-680 nm at R = 150000 with a stability of ~1cm / s . Improvement of a factor ~10-20 over HARPS short term accuracy. Long term ,stable calibration provided by a laser frequency comb tied to an atomic clock (prototype under study)

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CODEX : Cosmic Dynamics Experiment

Ly forest

Metal lines

QSO Absorption Spectrum, zem = 3

Experiment is unique in probing the dynamical effect of dark energy and doing so in the redshift range z = 1.5 - 4

Ly lines in very large number over the measurable redshift interval 2- 4. Narrow metallic lines can be used at lower redshift. Peculiar motions expected to be 10 times smaller than Hubble flow. Sufficient number of bright QSO

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CODEX : Cosmic Dynamics Experiment

Simulated result from 30 QSOrandomly distributed in the range 2 < z <4.5S/N = 3000 per 0.0125 Å pixel/epoch (no metal lines used)t = 20 years

Green points: 0.1 z bins, Blue: 0.5 z bins; Red line: Model with H0=70 Km/s/Mpc, Ωm=0.3 Ω=0.7

The cosmic signal is detected at >99% significance

SIMULATIONS Pasquini et al 2005

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CODEX : Cosmic Dynamics Experiment

“Immediate” science: Testing the Variability of the Fine Structure Constant α =e2/hc

Fundamental constants supposedly universal and invariable quantities

Measured variations would have far reaching consequences on current theories

Astronomical observations hold the potential to probe the value in the past (high z) by a measurement of relative shift of pairS of absortion lines with different sensitivies to the variation of α

Keck/Hires 143 systems Δα/α=(-0.57±0.11)×10-5

Murphy et al 2004

VLT/UVES 23 systems Δα/α=(+0.6±0.6)×10-6

Chand et al 2004

CODEX accuracy of / = 10 -8 will represent an improvement by two order of

magnitudes with respect to present measurements