Probing Dark Energy with Cosmological Observations Fan, Zuhui ( 范祖辉 ) Dept. of Astronomy Peking University

Outline

Introduction Cosmological Probes Current Status Future

Introduction

The development of cosmology is driven by observations

The universe is expanding ( ) – Big Bang

Hubble

0

R

The expansion is accelerating ( ) (1998, 1999)

0

R

Standard cosmological scenario: Einstein’s equations govern the evolution of the universe

R: scale factor of the universe

ii

GRk

RR

38

22

2

)3(3

4i

ii pG

RR

Normal matter:

The accelerating universe calls for the existence of dark energy with negative pressure

0

R

Understanding the nature of dark energy Theoretical physics: dark energy models Cosmology: extract constraints on dark energy from different observations

w=-1? w=constant? w(z) ?

Cosmological probes on dark energy

Global properties of the universe Geometry and expansion history of the

universe

Dynamical evolution of the large-scale structure of the universe

Expansion of the universe: SNe Ia: standard candle luminosity distance

Clusters of galaxies: SZ+X-ray angular diameter distance

Geometry of the universe: CMB: angular positions of the sound peaks sensitive to the total matter content

Dynamical evolution of the universe Large-scale structure of the universe galaxy redshift surveys power spectrum correlation function

detection of acoustic peak from the SDSS LRG sample

Eisenstein et al. astro-ph/0501171

Dark energy dependence

growth factor of density perturbations Cosmological distortion: AP test

The formation and evolution of clusters of galaxies abundance evolution: density growth volume element

gas fraction in clusters of galaxies assume the gas fraction fgas(z) invariant constraints on cosmology (dA(z) – z relation)

Gravitational lensing strong lensing weak lensing dynamical evolution of density perturbations angular diameter distances to the source, to the lens, and from lens to the source

Current status SNe Ia (Riess et al. 2004 astro-ph/0402512 ApJ, 607, 665)

Dark energy constraints

equation of state constant w

)(zwp

13.019.002.1 w 20.0

18.008.1 w

%)95(46.178.0 w

w(z) zwww '0

22.028.00 31.1 w 81.0

90.0' 48.1 w

Lyα+galaxy bias+SNe+CMB (Seljak et al. 2004, astro-ph/0407372, PRD, 71, 103515 (2005)) constant w

99.0w

)1/(1,)1()1( 22

10 zawawaww

cluster gas fraction +CMB+SN (Rapetti et al. MNRAS, 360, 555 (2005))

equation of state aett

tet wwwzzzwzww

00 ,

44.062.0

33.039.00 66.0,27.1

etww

weak lensing (M. Jarvis et al. astro-ph/0502243) CTIO lensing survey: 75 deg2, 19<R<23, 2*106 gal

dark energy constraint

constant w .).%95(894.0 156.0208.0 lcw

w(a)

the second peak corresponds to w(a=0)~1

not physically relevant

)1()( 0 awwaw a

.).%95(31.1,19.1 04.340.2

53.074.10 lcww a

As of today:

w=-1 (cosmological constant) is consistent

with all the observational data available to us

Slightly favor w<-1

Future SNe Ia SNAP Supernova/Acceleration Probe

Dark energy constraints

SNAP: weak lensing surveyDeep survey: 15 deg2, 250/arcmin2Wide survey: 300-1000 deg2 100/arcmin2Panoramic survey: 10000 deg2 40-50/acrmin2

Equation of state

CMB: Planck standard ruler: sound horizon baryon wiggles in matter power spectrum determination of other parameters Ωtotal, σ8, Ωm, Ωb, … ISW

Large-scale structure: LAMOST

LAMOST galaxy redshift survey (Sun, Su and Fan 2005) three redshift bins centered at 0.3, 0.4, and 0.5 distant observer approximation

With bins of higher redshifts, the constraints can be improved

Without distant-observer approximation z=0.2-0.4

a

Parameterization Priors systematic errors