institute for computational cosmology durham university shaun cole for carlos s. frenk institute for...

Institute for Computational Cosmology

Durham University

Shaun Cole for Carlos S. Frenk Institute for Computational

Cosmology, Durham

Cosmological simulations and forecasts for future surveys


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


Durham UniversityCMB anisotropies and large-scale

structure

Meiksin etal 99


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……)


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


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


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)


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


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


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


Durham University

Surveys: The Next Generation


Durham University

Springel etal 05


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 ?


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


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

)



Durham UniversityNon-linear evolution of

matter fluctuations

Log (P(k)/Plinear(k)) at z=1



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


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


Durham University

Absolute Magnitude limited

sample.

Galaxy clustering boosted relative to mass in real space

Galaxy bias in real space



Durham University

Boost in clusteringapproximates to a constant bias factor on large

scales.

Galaxy bias in real space



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


Durham University

Comparison of differentselections

e.g. colour, emission line

strength

Galaxy bias in redshift space

Angulo et al ‘07


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)


Durham University Recovered values

knl treated as a nuisance parameter.

Small offsets in but are they

significant?


Durham University Sample Variance

• 50 lower resolution “L-BASICC” simulations used to determine the sample variance.

• Particle mass 30 times larger.

• Bias not significant


Durham UniversityFractional error in

P(k)

(Feldman, Kaiser & Peacock 1994)


Durham University

Angulo et al (2008) tabulate rms error in for different fiducial samples within the BASICC simulation

Survey Forecasts


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


Durham University

EUCLID: DMD-based NIR spectra

See poster 21:

Andrea Cimatti


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


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


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


Durham UniversityPan-STARRS1 3Survey

gr i z

y


Durham University 3 size and depth

More than galaxies!810

Detected in griz and y


Durham University 3 size and depth

More than galaxies!810

Detected in griz only

More details will be presented by Stephanie Phleps later


Durham University

04.0

)1/(

zz

Photo-z accuracy

Initial estimates

indicate that for red/early type galaxies


Durham University Damping effect on BAO

Yan-chuan Cai et al (2008)


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


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

institute for computational cosmology durham university shaun cole for carlos s. frenk institute for...

Documents

s slide

w estimate of w

frenk institute

dfgrs pk

cosmological constant

panstarrs1 slide

cdm models

s measure