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