SCIENCE GOALS OF EXTREMELY LARGE TELESCOPES

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SCIENCE GOALS OF EXTREMELY LARGE TELESCOPES
Sandro DOdorico European Southern Observatory

RENCONTRES DE MORIOND Contents and Structures of
the Universe La Thuile, Val dAosta, Italy
March 18-25, 2006
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TELESCOPE GROWTH SINCE GALILEO Telescope size
driven by glas technology for primary surface
(lenses--gtmonolithic 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
LaSilla Obs
VLT Obs
USA and European Astronomers surveying sites for
4m telescopes on Atacama Cerro Morado, Chile,
1962 (ESO archive photo)
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

TMT
European ELT
GMT
Projected cost 500 700 Million EUROS ( x
1.15 ) Start of operation 2016
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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
JWST NIR and Thermal IR cameras and
spectrographs
ALMA antenna array for high angular resolution
submillimeter observations
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ACTUAL COLLECTING AREA OF LARGE TELESCOPES

Northern Hemisphere
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 (lt 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

• Detection and Characterization of Giant to
  Terrestrial Mass Planets
• Stellar Populations in external galaxies up to
  Virgo as tracers of the star formation history
  though the life of the universe
• Accurate redshift and characterization of SN up
  to redshift 2
• Detailed properties of galaxies and IGM 1 lt z lt
  5 (mass, metallicity, luminosity function, SFR,
  extinction, tomography and metal content of
  IGM)
• Redshift and characterization of galaxies up to
  z 10 (reionisation?), GRBs to the same z as
  probes of IGM
• Direct measurement of the expansion history of
  the Universe (E-ELT science case only)
• 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 5x5, 20mas sampling single
field 20 IFU 2 x 2 over
5 x 5 field / Z, J, H, K bands/

R1000-4000 /
throughput
(including telescope) gt 15/ ?limiting magnitude
Ks 23-24 in a few hours integration at S/N10 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 SPECTROGRAPH Science Cases
4, mapping of dark halos in ellipticals from GC
and PN Requirements Fieldgt40 sqmin, Spectral
range 310-1000 nm, Resolution 500-5000/
Throughput gt25 including telescope AO
requirements Improvement of seeing median
value by 20-30 with GLAO Flavors 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, 7 Requirements R 20000-150000,
throughput gt15 including telescope, AO
requirements Seeing median improvement by GLAO
desiderable Flavors HROS at TMT, CODEX at
E-ELT Challenges 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
Science Case and Instrument Concept Study carried
out by ESO, IoA Cambridge, Obs.Geneve and INAF
Trieste ( Pasquini et al . 2005)
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)
Magnitude of the effect H0 70 km/s/Mpc
?t 10 yr at z4 ?? 1 x 10 -6 A
?v 5 cm/s
redshift
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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 (gt10 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
range400-680 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 ? 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
Experiment is unique in probing the dynamical
effect of dark energy and doing so in the
redshift range z 1.5 - 4

QSO Absorption Spectrum, zem 3
Lya forest
Metal lines
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CODEX Cosmic Dynamics Experiment
SIMULATIONS Pasquini et al 2005

Simulated result from 30 QSO randomly distributed
in the range 2 lt z lt4.5 S/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 H070 Km/s/Mpc, ?m0.3
??0.7 The cosmic signal is detected at gt99
significance
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CODEX Cosmic Dynamics Experiment
Immediate science Testing the Variability of
the Fine Structure Constant a 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 a
VLT/UVES 23 systems ?a/a(0.60.6)10-6 Chand
et al 2004
Keck/Hires 143 systems ?a/a(-0.570.11)10-5
Murphy et al 2004
CODEX accuracy of ??/? 10 -8 will represent an
improvement by two order of magnitudes with
respect to present measurements
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