Filipe B. Abdalla, Steve Rawlings Oxford, Sarah Bridle UCL, Chris Blake UNSW

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Cosmological experiments in thewith the SKA
Filipe B. Abdalla, Steve Rawlings (Oxford), Sarah
Bridle (UCL), Chris Blake (UNSW)
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The SKA

• An extremely powerful survey telescope at with
  the capability to follow up individual objects
  with high angular and time resolution
• 1 km2 collecting area
• limited gains achievable by reducing receiver
  noise need more microwave photons
• Frequency range 0.1 25 GHz
• Angular resolution 0.1 arcsec _at_ 1.4 GHz
• 15-country international collaboration
• Technology selection in 2008 initial operations
  2015 full operations 2020

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SKA whats interesting?

• Sensitivity 100 x VLA
• Large FOV 1-100 sq. deg. at 1.4 GHz
• Goal of multi-beam instrument, at least at lower
  frequencies
• Innovative designs could have
• extremely large FOV and/or
• multi-beaming

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FOV
1 deg2 (minimum) field-of-view
With spectra of every object in the field
possibility of 50-100 sq deg.
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What will the SKA see?Normal/Starburst galaxies
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What will the SKA see?

• 109 galaxies in 3D over 20000 deg2 in a few
  years.

• 1010 galaxies in 2D over 20000 deg2 in a few
  years.

Results agree well with other results including
semi-analytic calculations.
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Universe is flat(ish), dark energy exists
Empty DA10 kpc/arcsec Flat DA0.05
kpc/arcsec Angle q s / DA
Note h prior, orthogonal (SN) constraints and
theoretical prejudice (that the Universe IS
spatially flat).
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Planck NOT the dark energy machine
Wm h2 to 1 BUT Even assuming flatness,
uncertainties in our sound horizon size
(sensitive to mix of baryons/CDM/HDM) makes our
cosmic ruler squashable (at the 2 level) - and w
cant be measured.
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Experiment I wiggles
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Very high precision P(k)
Galaxy redshifts over 1000-times volume V of
2dF/SDSS by measuring redshifts for all galaxies
out to z2. Errors (due to cosmic variance) scale
as sqrt(V) And errors much less correlated if the
window function is sharp in k space. Will find
wiggles in the baryons (traced by galaxies) and
the turnover.
But bias is likely to be scale-dependent, CARE!
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From a survey to a P(k)
Galaxies are found in RA, DEC, and z.
In order to measure P(k). We have assume a
cosmology To change from (RA,DEC) to
(k_par,k_per)
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Experiment I wiggles
Galaxies are located in RA, DEC and z. If the
wrong cosmology is assumed, we notice a
distortion on the power spectrum.
Blake Glazebrook 2003
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Claims of baryonic oscillation measurements.
Correlation function has a peak at 100 h Mpc.
Statistical significance of these observations is
very small but it Is clear that it will be
possible to use these features in future
experiments.
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Experiment I wiggles
Care what k_max are you allowed to use on a
P(k) measurement at high z?
Tangential rods can cancel s, so that
DA(zzeff) / DA (z1000) qCMB /
qwiggles Radial rods extra information from
isotropy (c.f. AP test), and zlt2 key regime. As s
now measured (independent of baryons etc),
finally have a standard rod.
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Experiment II Weak lensing
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Experiment II Weak lensing
Simulate images using the local luminosity
function for starburst galaxies from Sadler et
al. (2002). Then attempt to measure their shapes
using IMCAT. 100 galaxies/arcmin2 usable for
shear measurement.
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Experiment II Weak lensing
Requires (i) good image quality and low
systematics for measuring shear (ii) source
density 100 arcmin-2 to beat down noise (iii)
wide-field to beat down cosmic variance
(particularly away from strongly non-linear
scales) (iv) lensing tomography.
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Future Experiments
Wiggles Having redshifts for all 109 galaxies
out to redshift 2 in a considerable fraction of
the sky. Have large cosmic volumes, access to
large scales (where nuisances like bias and
non-linear growth are minimised), narrow
k-space window functions, and different
degeneracies from CMB. Shear Machine delivering
good quality (0.1 arcsec, low systematic, stable
psf) imaging of gt1010 galaxies in at least two
redshift bins (say at 1 and 2) across whole
sky. Planck essential to calibrate the size scale
of the wiggles. i.e. prior on matter
density Optical surveys SNAP (in space),
FMOS/KAOS (from ground) may take next steps (but
note HIFAR), but all limited by FOV, so will have
fsky ltlt 1.
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FOV
1 deg2 (minimum) field-of-view
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Prospects are good
Measure wcst to dw lt 0.01 on each experiment
independently Results are comparable if not
better than results predicted by the SNAP
satellite. Nevertheless systematics are different
and results are complementary.
Different degeneracies because shear depends on
growth of mass fluctuations as well as DA.
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Dark energy now an SKA Key Science Project
By 2020, SKA could totally dominate LSS
measurements, locating in 3D 109 galaxies to
redshifts 2 and 1010 galaxies in 2D over the
entire sky. This will, with measurements of the
CMB, be the only clean way of measuring LSS on
Gpc scales. It should determine whether or not
Einsteins cosmological constant is Dark Energy.
Decisions on SKA technology will be taken over
the next few years, and if a wide field
capability is available for the SKA, it will play
a unique role in cosmological experiments in the
period 2015-2020!