Post on 15-Dec-2015
Institute for Computational Cosmology
Durham University
Shaun Cole for Carlos S. Frenk Institute for Computational
Cosmology, Durham
Cosmological simulations and forecasts for future surveys
Institute for Computational Cosmology
Durham University Outline
Baryonic Acoustic OscillationsOriginMeasurementsDistortion due to non-linear evolution, peculiar
velocities and galaxy bias
Future Surveys and ForecastsSpectroscopic and Photometric SurveysEUCLID and Pan-STARRS1
Institute for Computational Cosmology
Durham UniversityCMB anisotropies and large-scale
structure
Meiksin etal 99
Institute for Computational Cosmology
Durham UniversityBaryon oscillations in the power spectrum
ra
eq
s
m
daaa
c
Hs
0 2/12/10 )(
1
dx
dz
c
H0m1/ 2
1
(1 z)3 (m 1 1)(1 z)3(1w )
Comoving sound horizon at trec
(depends mostly on mh2
and weakly on bh2)
“wavenumber” of acoustic oscillations: kBAO= 2/s
Comoving distance/redshift:
(depends on mh2 and w)
Apparent size of standard ruler depends on cosmology
dark energy eqn of state parameter w(e.g. Eisenstein & HU 1998; Blake & Glazebrook 2003, 2005; Seo & Eisenstein 2003; 2005……)
Institute for Computational Cosmology
Durham UniversityThe final 2dFGRS power spectrum
2dFGRS P(k) well fit by CDM model convolved
with window function
Cole, Percival, Peacock, Baugh, Frenk + 2dFGRS ‘05
Institute for Computational Cosmology
Durham UniversityThe final 2dFGRS power spectrum
CDM model
CDM convolved with window
2dFGRS P(k) well fit by CDM model convolved
with window function
Cole, Percival, Peacock, Baugh, Frenk + 2dFGRS ‘05
Institute for Computational Cosmology
Durham UniversitySDSS LRG correlation function
Eisenstein et al. 05
Again, CDM models fit the correlation function
adequately well (although peak height is
slightly too large; assuming ns=1, h=0.72)
bh2 =0.024, mh2 =0.133±0.011,
b/m= 0.18
s)
Institute for Computational Cosmology
Durham University
Constraints on w from SnIa, WMAP and LSS
2cwp
Spergel et al 2006
w
w
mm
Cosmological constant
Assume w=const (cosmological constant)
w=-0.9 0.1
Institute for Computational Cosmology
Durham University
s = comoving sound horizon at trec
Depends on physical parameters
“Wavenumber” of acoustic oscillations is:
kBAO= 2/s
Measure kA in redshift survey:
conversion z k in P(k) depends on geometry and expansion history and so on w
Estimate of w from P(k)
Consider idealized case:
•All cosmological parameters apart from w known
BAOBAO kk truerecovered / factor,stretch
Institute for Computational Cosmology
Durham University
s = comoving sound horizon at trec
Depends on physical parameters
“Wavenumber” of acoustic oscillations is:
kBAO= 2/s
Measure kA in redshift survey:
conversion z k in P(k) depends on geometry and expansion history and so on w
Estimate of w from P(k)
Consider idealized case:
•Angular size of sound horizon at last scattering kept fixed
Stretch factorBAOBAO kk truerecovered / factor,stretch
Institute for Computational Cosmology
Durham University
linear theory
The non-linear mass power spectrum is
accurately determined by the
Millennium simulation over large
range of scales
The mass power spectrum
z=0
z=1
z=3.05
z=7
z=14.9 2
(k)
k [h/Mpc]
Lbox=500Mpc/h
Baryon wiggles in the galaxy distribution
Springel et al 2005
Power spectrum from MS divided by
a baryon-free CDM spectrum
Galaxy samples matched to
plausible large observational
surveys at given zz=0z=1
z=3z=7
DMgals
Millennium simulation
The effective
keq changes
as does kSilk,
but does kBAO ?
Institute for Computational Cosmology
Durham University
N-body simulations of large cosmological volumes
BASICC
L=1340/h Mpc
N=3,036,027,392
20 times the Millennium volume
Halo resolution: (10 particle limit)5.5 e+11/h Mpc
130,000 cpu hours on the Cosmology Machine
Angulo, Baugh, Frenk & Lacey ‘07
Institute for Computational Cosmology
Durham University
BASICC simulationdark matter real space
P(k) divided by linear theory P(k),
scaling out growth factor
Non-linear evolution of matter fluctuations
P(k
)/P
line
ar(k
)
Angulo, Baugh, Frenk & Lacey ‘07
Institute for Computational Cosmology
Durham UniversityNon-linear evolution of
matter fluctuations
Log (P(k)/Plinear(k)) at z=1
Angulo, Baugh, Frenk & Lacey ‘07
Institute for Computational Cosmology
Durham University
Coherent bulk flows boost large scale power
(Kaiser 1987)
Redshift space distortions
Peculiar motions distortclustering pattern
Motions of particles insidevirialised structures damp power at high k
Institute for Computational Cosmology
Durham University
Peculiar motions distortclustering pattern
Boost in power on largescales due to coherent
flows
Damping at higher k affects DM but not the
halos
In z-space, halo bias is scale-dependent
Redshift space distortions
Halos M> 1012 Mo
Dark matter
Redshift space
Institute for Computational Cosmology
Durham University
Absolute Magnitude limited
sample.
Galaxy clustering boosted relative to mass in real space
Galaxy bias in real space
Angulo, Baugh, Frenk & Lacey ‘07
Institute for Computational Cosmology
Durham University
Boost in clusteringapproximates to a constant bias factor on large
scales.
Galaxy bias in real space
Angulo, Baugh, Frenk & Lacey ‘07
Institute for Computational Cosmology
Durham University
Galaxy P(k) cannotbe reproduced by multiplying mass P(k) by constant factor in redshift
space.
Galaxy bias in redshift space
In z-space, galaxies have a scale-dependent bias out to k~0.1
Institute for Computational Cosmology
Durham University
Comparison of differentselections
e.g. colour, emission line
strength
Galaxy bias in redshift space
Angulo et al ‘07
Institute for Computational Cosmology
Durham University Fit BAO oscillationsRemove effect of scale dependent bias by fitting a smooth spline and then take ratio R(k)=P(k)/Psmooth(k).
Fit ratio, R(k), to determine both the stretch factor, and the damping scale,
knl . (Percival et al 2008)
Institute for Computational Cosmology
Durham University Recovered values
knl treated as a nuisance parameter.
Small offsets in but are they
significant?
Institute for Computational Cosmology
Durham University Sample Variance
• 50 lower resolution “L-BASICC” simulations used to determine the sample variance.
• Particle mass 30 times larger.
• Bias not significant
Institute for Computational Cosmology
Durham UniversityFractional error in
P(k)
(Feldman, Kaiser & Peacock 1994)
Institute for Computational Cosmology
Durham University
Angulo et al (2008) tabulate rms error in for different fiducial samples within the BASICC simulation
Survey Forecasts
Institute for Computational Cosmology
Durham University
Scaling error forecasts to different surveys:
delta(w) ~ 1/sqrt (V) x [1 + 1/(n P)]
Error on the measured power
BAO method: virtually free of systematics (c.f. lensing, SNIa)
(i) Sample variance
(ii) Shot noise
P = powern = mean no density
Institute for Computational Cosmology
Durham University
EUCLID: DMD-based NIR spectra
See poster 21:
Andrea Cimatti
Institute for Computational Cosmology
Durham University EUCLID: Spectroscopy
Category
Item Requirement
Spectroscopic BAO Survey
Redshift Accuracy
σz < 0.001
Spectral Range
0.9-1.7 micron
Number of spectra
1.65x108 galaxiesSampling > 33%
Limiting magnitude and redshift distribution
H(AB)=22 mag corresponding to 0<z<2
Deep spectroscopic sample
Photo-z calibration
105 redshifts down to H(AB)=24 mag
Institute for Computational Cosmology
Durham University
Projected BAO data for planned surveys at z=1
Projections based on mock catalogues
made from large N-body simulation plus semi-analytic galaxy formation
model
EUCLID
Institute for Computational Cosmology
Durham University Main future BAO surveys
Name N(z) / 106 Stretch Dates Status
SDSS/2dFGRS 0.8 3.5% Now Done
WiggleZ 0.4 2% 2007-2011 Running
FastSound 0.6 2.8% 2009-2012 Proposal
BOSS 1.5 1% 2009-2013 Proposal
HETDEX 1 1.5% 2010-2013 Part funded
WFMOS >2 0.8% 2013-2016 Part funded
ADEPT >100 0.2% 2012+ JDEM
EUCLID >100 0.15% 2017+ ESA
SKA >100 0.2% 2020+ Long term
Institute for Computational Cosmology
Durham University 3 size and depth
More than galaxies!810
Detected in griz and y
Institute for Computational Cosmology
Durham University 3 size and depth
More than galaxies!810
Detected in griz only
More details will be presented by Stephanie Phleps later
Institute for Computational Cosmology
Durham University
04.0
)1/(
zz
Photo-z accuracy
Initial estimates
indicate that for red/early type galaxies
Institute for Computational Cosmology
Durham University Damping effect on BAO
Yan-chuan Cai et al (2008)
Institute for Computational Cosmology
Durham University Future photo-z BAO surveys
Name N(z) / 106 Stretch Dates Status
PS1 >100 0.5% 2009-2013 Funded
DES 50 <1% 2010-2014 Funded
PAU(BAO) 14 0.4% 2014+ planned
Institute for Computational Cosmology
Durham University Summary
• BAO have an important future as a cosmic standard ruler used to constrain D(z) and hence Dark Energy.
• Systematic errors are not yet dominant, but more theoretical work is needed to ensure this remains true for the forthcoming generation of surveys
• In advance of the long term space projects, photo-z surveys promise interesting constraints