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

The expansion is accelerating ( ) (1998, 1999)

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

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

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/

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 f gas (z) invariant  constraints on cosmology (d A (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 astro-ph/ ApJ, 607, 665 )

Dark energy constraints equation of state constant w

w(z)

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

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

equation of state

weak lensing (M. Jarvis et al. astro-ph/ ) CTIO lensing survey: 75 deg 2, 19<R<23, 2*10 6 gal

dark energy constraint constant w

w(a) the second peak corresponds to w(a=0)~1 not physically relevant

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 survey Deep survey: 15 deg 2, 250/arcmin 2 Wide survey: deg 2 100/arcmin 2 Panoramic survey: deg /acrmin 2

Equation of state

CMB: Planck standard ruler: sound horizon  baryon wiggles in matter power spectrum determination of other parameters Ω total, σ 8, Ω m, Ω b, … 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=

a

Parameterization Priors systematic errors