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Transcript Transparencies - Rencontres de Moriond

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
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
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
Projected cost : 500 – 700 Million EUROS (~ x 1.15 $)
Start of operation: 2016
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GMT
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
ALMA : antenna array for high angular
resolution submillimeter observations
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JWST: NIR and
Thermal IR cameras
and spectrographs
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 (< 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
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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 2324 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 SPECTROGRAPH
Science Cases: 4, mapping of dark halos in ellipticals from GC and PN
Requirements: Field>40 sqmin, Spectral range : 310-1000 nm, Resolution =
500-5000/ Throughput >25% 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
>15% 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
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Nr of QSO from SDSS observable in 3hrs at
high resolution, for different S/N, as function
of telescope diameter (credit TMT MTHR
study)
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)
z 
dz
 (1  z ) H 0  H (te )
dt
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
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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  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
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CODEX : Cosmic Dynamics Experiment
SIMULATIONS
Pasquini et al 2005
Simulated result from 30 QSO
randomly distributed in the range
2 < z <4.5
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
H0=70 Km/s/Mpc, Ωm=0.3 Ω=0.7
The cosmic signal is detected at
>99% significance
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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
VLT/UVES 23 systems
Δα/α=(+0.6±0.6)×10-6
Chand et al 2004
Keck/Hires 143 systems
Δα/α=(-0.57±0.11)×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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