Transcript Study Scientist Report

Euclid
A Space Mission to Map the Dark
Universe
R. Laureijs (ESA), A. Refregier (CEA), A. Cimatti
(Univ. Bologna), on behalf of the (growing) Euclid
Community
Slide 1
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Dark Energy - Leopoldina
Munich
Opportunity
• ESAs Cosmic visions programme has selected a
dark energy mission as a possible candidate for
a launch slot in 2017.
• Euclid will address the outstanding questions in
cosmology
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Nature of the Dark Energy
Nature of the Dark Matter
Initial conditions
Theory of Gravity
Slide 2
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Munich
Outline
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Slide 3
11 Oct 2008
Euclid selection and concept
Science Objectives
Mission
Payload
Status and programmatics
Dark Energy - Leopoldina
Munich
Selection of ESAs Dark Energy
Mission
• Dark energy is recognized by the ESA Advisory
Structure as the most timely and important science topic
among the M mission proposals and is therefore
recommended as the top priority.
• Dark energy was addressed by two Cosmic Visions M
proposals:
– DUNE (PI: A. Refregier-CEA Saclay) – All sky visible and NIR
imaging to observe weak gravitational lensing
– SPACE (PI: A. Cimatti – Bologna Univ.) – All sky NIR imaging
and spectroscopy to detect baryonic acoustic oscillations
patterns
• An Advisory Team recommended a concept for a single
M-Class Dark Energy Mission
Slide 4
11 Oct 2008
Dark Energy - Leopoldina
Munich
Euclid’s Concept
• Named in honour of the pioneer of geometry
• Euclid will survey the entire extra-galactic sky (20 000
deg2) to simultaneously measure its two principal dark
energy probes:
– Weak lensing:
• Diffraction limited galaxy shape measurements in one broad visible
R/I/Z band.AB=24.5 mag
• Redshift determination by Photo-z measurements in 3 NIR bands
(Y,J,H) to H(AB)=24 mag, 5σ point source
– Baryonic Acoustic Oscillations:
• Spectroscopic redshift survey for 33% of all galaxies brighter than
H(AB)=22 mag, σz<0.001
• With constraints:
– Aperture: max 1.2 m diameter
– Limited number of NIR detectors
– Mission duration: max ~5 years
Slide 5
11 Oct 2008
Dark Energy - Leopoldina
Munich
WL: shear measurement
space
weak lensing shear
ground
In Space: availability of small and stable PSF:
 larger number of resolved galaxies
 reduced systematics
Slide 6
11 Oct 2008
Dark Energy - Leopoldina
Munich
Typical cosmic
shear is ~ 1%,
and must be
measured with
high accuracy
WL: Obtaining NIR photometric redshifts
OPT+IR
OPT
zphoto
zspec
zspec
Abdalla et al.
• Will need redshifts for 109 galaxies − photo-z error possible to ~5% in
combination with ground-based Pan-Starrs survey etc.
• But need 1-2 micron IR for z >1 − impossible from ground (sky brightness)
• Need >105 spectroscopic redshifts for calibration
Slide 7
11 Oct 2008
Dark Energy - Leopoldina
Munich
NIR Spectroscopy: DMD based multi-object slit
spectroscopy
DMD=
Digital
Micro-mirror
Device
Slide 8
11 Oct 2008
Dark Energy - Leopoldina
Munich
Euclid’s Primary Science
Objectives
Issue
Target
Dark Energy
Measure the DE parameters wn and wa to a precision
of 2% and 10%, respectively, using both expansion
history and structure growth.
Dark Matter
Test the Cold Dark Matter paradigm for structure
formation, and measure the sum of the neutrino
masses to a precision better than 0.04eV when
combined with Planck
The seeds of cosmic
structures
Improve by a factor of 20 the determination of the
initial condition parameters compared to Planck alone
Test of General
Relativity
Distinguish General Relativity from the simplest
modified-gravity theories, by measuring the growth
factor exponent γ with a precision of 2%
Slide 9
11 Oct 2008
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Munich
Other Probes
• Besides its two principal dark energy probes, Euclid will
obtain information of:
– Galaxy clustering: the full power spectrum P(k)
• Determination of the expansion history and the growth factor using
all available information in the amplitude and shape of P(k)
– Redshift-space distortions:
• Measures the growth rate (derivative of growth factor) from the
redshift distortions produced by peculiar motions.
– Number density of clusters
• Measures a combination of of growth factor (from number of
clusters) and expansion history (from volume evolution).
– Integrated Sachs-Wolfe Effect
• Measures the expansion history and the growth.
Slide 10
11 Oct 2008
Dark Energy - Leopoldina
Munich
Why is the combined mission so powerful
High precision and accurate DE measurements require a
combination of two or more probes. Euclid aims at the
most promising dark energy probes: an all sky survey of
weak lensing and galaxy redshifts.
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The weak lensing will reconstruct directly the distribution of the dark matter
and the evolution of the growth rate of dark matter perturbations with
redshift.
The baryon acoustic oscillations act as standard rods,determine P(k) and
provide a measure of H(z) and hence w(z). They also map out the evolution
of the baryonic component of the Universe.
Together, these enable many systematic effects to be controlled – for
example, intrinsic alignments in weak lensing, bias factors in baryon
acoustic oscillations.
Both act as independent dark energy probes. If they differ, we learn about
modifications to GR.
Slide 11
11 Oct 2008
Dark Energy - Leopoldina
Munich
Predicted redshift dependence of w(z) errors
Planck prior is used. The
errors are calculated using
Fisher matrices using a
w(a)=w0+(1-a)wa model,
hence the caveat that the
errors shown here are
correlated (from J. Weller).
Slide 12
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Euclid’s Legacy
 Visible/NIR imaging survey: morphologies and vis/NIR
colors for billions of galaxies out to z~2, 3D dark matter
map
 Spectroscopic survey: 3D map of the luminous matter
distribution, spectra of ~200 million galaxies to z~2
 Deep survey: infrared imaging to H(AB)=26 and
spectroscopy to H(AB)=24, galaxies with 2<z<7. Objects
at z>7 and up to z~10 can be colour-selected from
the Y,J,H colours
 Impossible to reach from the ground
Slide 13
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Mission profile (1)
CDF study case
Launcher
SOYUZ ST 2-1b from Kourou
Launch mass margin: 28%
Sky coverage
20 000 sq. degrees extragalactic sky
Two galactic polar caps, latitudeb> 30°
Solar aspect angle adjusted for scan optimisation
Slide 14
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Mission profile (2)
Orbit
Large amplitude Lissajous around SEL2
Free insertion, 30-day transfer time
DeltaV budget: 50 m/s
Orbit maintenance: 1 manoeuvre/month
Spacecraft
Body-mounted solar array, 3-axis stabilised platform
Relative pointing error: 25 marcsec with FGS
Attitude control with proportional cold gas system
Hydrazine propulsion for orbit manoeuvres
Satellite mass (wet): 1540 kg
Communications
Housekeeping in X-band, Science telemetry in K-band
700 Gbits/day after compression
4 hours/day link with Cebreros 35-m antenna
Mission duration: 5 years including commissioning
Slide 15
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First Assessment:
All mission
elements are
standard and
feasible
Payload (1)
Telescope
1.2 meter Korsch TMA
Thermal
Passive cooling
CCDs at T=170 K
NIR detectors at T=140 K
Power
One power conditioning unit per instrument
Total payload: ~200 W peak
Data-handling
Spectroscopy target selection
Full frame images lossless compression
NIR detectors noise reduction
Slide 16
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Payload (2)
3 instruments
Visible Imaging VIS: 0.21” PSF at 800 nm, 0.1”/pixel
NIR Photometry NIP: 0.33”/pixel, 3 bands (Y, J, H)
NIR Spectroscopy NIS: 0.9-1.7 m, set of 3 cameras,
multi-objects (micro-mirror array), R~400
Each of them with a field of view ~0.48 deg2
Observation mode
-Step and stare case fully investigated
-Continuous scanning requires a de-scan mechanism
for infrared channels
NIS
NIP
Payload mass
~660 kg, including 300 kg for the 3
instruments
First Assessment: High
technological readiness with
some level of complexity
Slide 17
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VIS
Status and programmatics
• Two independent industrial studies have started on the
system (including mission and payload):
1 year study until Sep 2009
• Two payload consortia:
– Euclid Imaging Channels (EIC),
headed by A. Refregier (CEA, France)
– Euclid Near-Infrared Spectrometer (ENIS), headed by A. Cimatti
(Univ Bologna, Italy)
10 month study until Aug 2009
• DMD flight qualification study started
• Overall coordination by ESA and the Science Study
Team
• Down selection in 2009
– Definition phase 2010-2012
– Implementation phase 2012-2017
Slide 18
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