KIAS cosmology 20081 Peculiar velocity: a window to the dark universe 张鹏杰 ( Zhang, Pengjie)...
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Transcript of KIAS cosmology 20081 Peculiar velocity: a window to the dark universe 张鹏杰 ( Zhang, Pengjie)...
KIAS cosmology 2008 1
Peculiar velocity: a window to the dark universe张鹏杰 ( Zhang, Pengjie)
中国科学院上海天文台Shanghai Astronomical Observatory
Chinese Academy of Science
Based onZPJ, Michele Liguori, Rachel Bean & Scott Dodelson, 2007, PRLZPJ & Xuelei Chen, 2008, PRDBhuvnesh Jain & ZPJ, 2008, PRDZPJ, Hume Feldman, Roman Juszkiewicz, Albert Stebbins, 2008, MNRASZPJ, 2008, arxiv: 0802.ZPJ, Rachel Bean, Michele Liguori, & Scott Dodelson, 2008, arxiv:0809.
KIAS cosmology 2008 2
The dark universe
The visible world
Dark matter?
Dark energy?
Modified gravity?
KIAS cosmology 2008 3
Windows to the dark universe
z ~ 1000 z ~ 30 z ~ 6 z ~ 0z ~ 1000 z ~ 30 z ~ 6 z ~ 0z ~ 1000 z ~ 30 z ~ 6 z ~ 0
21cmSoon to detect
KIAS cosmology 2008 4
lensing
SNe Ia
BAOcluster abundance
peculiar velocity
CMBWe are able to put everything together to reconstruct the elephant!
the dark universe
KIAS cosmology 2008 5
The dark energy task force recommends fourprobes of the expansion: SN and BAOprobes of structure growth: weak lensing and cluster abundance
Figure of merit for stage IV space projects
Peculiar velocity as the fifth!!
KIAS cosmology 2008 6
• Matter distribution in our universe is inhomogeneous
• Gravitational attraction arising from inhomogeneity perturbs galaxies and causes deviation from the Hubble flow
v
r
v
r
peculiarvelocity
v=Hr v=Hr
KIAS cosmology 2008 7
What makes peculiar velocity special and important to probe the dark universe?
At scales larger than galaxy clusters, only respond to gravity
In linear regime, honest tracer of matter distribution
Necessary for the complete phase-space description of the universe
dt
vd
dt
av)d(
01
vadt
d
KIAS cosmology 2008 8
GREAT attractor(s), with far more mass than expected, must exist in order to pull the Milky way at ~ 600 km/s with respect to CMBSuch gigantic structures should be no coincidence, if we believe in the cosmological principle
Great attractor
Shapely concentration
Early applications of peculiar velocity: (1) A brave new world with gigantic structures
KIAS cosmology 2008 9
Early applications of peculiar velocity: (2) road to the standard LCDM cosmology
• Largely based on peculiar velocity measurements of local and nearby galaxies, some cosmologists (e.g. Jim Peebles) argued that the the cosmological constant may exist and account for ~80% of the energy budget of the universe, in early 80s.
KIAS cosmology 2008 10
How to measure peculiar velocity?Traditional method
v
r
Subtract the Hubble flow to obtain the peculiar velocity
v=Hr
Measure the recession velocity from the redshift
Measure the distance through FP,TF,FJ,SN, etc.
Error increases linearly with distance.Can not apply to cosmological distances
KIAS cosmology 2008 11
New probes of large scale peculiar velocity which do not rely on distance indicators
These new probes of large scale peculiar velocity do not rely on subtracting the Hubble flow, so are applicable to z~1
• Redshift distortion (bonus of BAO surveys)
• The kinetic Sunyaev Zel'dovich effect of galaxy clusters
• Type Ia supernovae at z<~0.5
KIAS cosmology 2008 12
)()1)(()( 22
H
kuFukPkP g
sg
)(ln
ln ; z
ad
Ddf
b
fm
g
Redshift distortion and cosmology
Peacock et al. 2001
Kaiser effectinduced by large scale coherent infall
Finger of Godinduced by small scale random motion
KIAS cosmology 2008 13
A sensitive measure of gravity
Guzzo et al. 2008
Acquaviva et al. 2008
Spectroscopic redshift surveys•Measure beta from the anisotropy•Measure galaxy bias•Obtain f
Current measurements
KIAS cosmology 2008 14
BAO surveys (Refer to the WiggleZ talk) are reshaping the field of redshift distortion measurement!(1) the expansion from BAO and(2) the growth rate from redshift distortion
Amendola, Quercellini &Giallongo 2004
BAO
BAO+RD
RD helps to improve dark energy constraints
However, the improvementis not significant for future big surveysBecause if smooth dark energy, BAO and RD basically probes the same H(z)
KIAS cosmology 2008 15
Strong tests on gravity
Yun Wang 2007See also Eric Linder 2007
DE and MG can have nearly degenerate H(z)
But their structure growthrate can be very different
KIAS cosmology 2008 16
Testing the consistency relation through spectroscopic redshift surveys
Acquaviva et al. 2008
=0 in GR+smooth dark energy
BAO+CMB
Redshift distortion
KIAS cosmology 2008 17
Physics behind the consistency relation
02
33/32
200
22
2
aH
H
aaH
dadH
da
d
da
d
2 ( ) 8 G
= / 1
18
2visible
uv uv uv uvR g R g GT CDMuvT
KIAS cosmology 2008 18
~
1
~
~ ~
( ) gravity:
DGP gravity: 1
TeVeS: ( ,other fields)
R
Geff f
eff
eff eff uv
f R G
G
G G g
/ 1 2DE: ( ) 12 (1 )
DGP: = (z) 1
k G w
2 ( ) 8 G
=effG
)10(1 5 O
ZPJ et al. 2007; Amendola et al. 2007Caldwell et al. 2007; Bertschinger& Zukin. 2008
Also Uzan 2006Hu & Sawicki 2007
KIAS cosmology 2008 19
Testing the (generalized) Poisson Equation
)d 2s= ( - )W( ,
2 ( ) 8 G
=
Gravitational lensing
v H
f
fH
/
from peculiar velocity
?
Galaxy redshifts to recover redshift information (2D ->3D)
KIAS cosmology 2008 20
Weak lensingCosmic shear
DES, LSST, SNAP, Euclid, SKA, etc.Cosmic magnification
SKACosmic microwave and 21cm backgrounds
Large scale peculiar velocities (bulk flows)Galaxy redshift distortion from spectroscopic redshi
ft surveysStage III: LAMOST, BOSS, WFMOS, etc.Stage IV: ADEPT, Euclid, HSHS, SKA, etc.
Other methods (KSZ, SNe Ia.... )
KIAS cosmology 2008 21
A discriminating probe of gravity
•No dependence on galaxy bias
•No dependence on the shape and amplitude of the matter power spectrum, in the linear regime
•Scale independent in LCDM and QCDM, whose amplitude is completely fixed by the expansion rate
•Contains smoking guns of modifications in gravity and particle physics•Changes in the amplitude•Violation of the scale independence
22
( ) ( ) 1gG
g
PE
P
Poisson equation!
Linear density growth rate
galaxy-galaxy lensing
redshift distortion
f
KIAS cosmology 2008 22
LCDMf(R)DGPMOND
ZPJ, Liguori, Bean & Dodelson2007, PRL
• EG will be measured to 1% level accuracy within two decades
• Promising to detect one percent level deviation from general relativity+canonical dark energy model (if systematics can be controlled)!
KIAS cosmology 2008 23
One can further construct an estimator of η≡-Φ/ΨLensing: Φ-Ψ; Peculiar velocity: Ψ
ZPJ et al. 2008b
Velocity measurement forecasted for SKA
?
KIAS cosmology 2008 24
ZPJ et al. 2008b
•eta can be measured to 10% accuracy.
•Errors in eta is larger than errors in E_G•Even so, eta can have stronger discriminating power, in some cases.
•η of DGP differs significantly from that of LCDM. (EG of DGP is very close to that of LCDM.)
•eta and E_G are complementary
•DGP with high Omeag_m
SKA forecast
DGP
MONDTeVeS
dark energy with anisotropic stress
KIAS cosmology 2008 25
Layers of assumptions/approximations
2 412( , ) ( 2 ..) ( )s
g g gv vP k u P u P u P F ku
2 412( , ) ( 2 ) ( )s
g g gv vP k u P u P u P F ku
e.g. Matsubara 2007
e.g. Tegmark et al. 2002,2004Scoccimarro 2004ZPJ et al. 2007, ZPJ 2008
deterministic bias
e.g. Peacock et al. 2001;Guzzo et al. 2008;Amendola et al. 2004Linder 2007;Wang 2007More uncertainties:
•Linear evolution•Light cone•distant observer assumption•.....
F: Lorentz or Gaussian
2 212( , ) (1 ) ( ) ( )s
g gP k u u P k F ku
scale independent galaxy bias
e.g. Acquaviva et al. 2008
KIAS cosmology 2008 26
On real data
• Tegmark et al. 2002 on 2dF
• Tegmark et al. 2004, on SDSS
One can measure the gg,gv,vv power spectra simultaneously.
errors (vv)>errors(gv)>errors(gg)
KIAS cosmology 2008 27
Forecast for future surveys the Square Kilometer Array (SKA) as an example
Future surveys can detect (1) stochasticity in galaxy bias (2) scale dependence in galaxy bias
We are no longer able to use the usual Kaiser formula.
At such stage, more detailed check against current RD model and/or more accurate RD modeling are required
Other velocity probes?
ZPJ 2008
SKA, ADEPT, HSHS, Euclid
KIAS cosmology 2008 28
CMB photonfree electron
scattered CMB photon
pgksz vMS
vp: bulk velocityscattering probability
The kinetic Sunyaev Zel'dovich effect of galaxy clusters
Recently, the South Pole Telescope (SPT) has for the first time discovered clusters, through the thermal SZ effect!
KIAS cosmology 2008 29
Measuring velocity from KSZ
Allows statistical measurement of vp (vp power spectrum)
Measure vp of individual clusters
• Requires other measurements to infer Mg
– Thermal SZ to have MgT– X-ray to have T
ZPJ et al. 2008, MNRAS
pgksz vMS
Haehnelt & Tegmark 1996;Kashlinsky & Atrio-Barandela 2000; Aghanim et al.2001; Atrio-Barandela et al. 2004; Holder 2004
Statistical errors>systematical errors
KIAS cosmology 2008 30
SNe Ia as cosmic speed censors at intermediate redshift ~0.5
ZPJ & Chen, 2008, PRD
Peculiar velocity causes fluctuations in SNe Ia flux
Already allow velocity measurement at z<0.1
At z>0.1, lensing dominates over velocity
Measure the 3D power spectrum ofSNe Ia flux, in which noise can be significantly suppressed
signal (velocity)
Noise (lensing)
z=0.5
KIAS cosmology 2008 31
If 3 or more independent LSS variables can be measured, modified gravity models can be unambiguously discriminated from DE/DM
Weak lensingPeculiar velocity......
Bhuvnesh Jain & ZPJ, 2008, PRD
Peculiar velocity is indispensable for ultimate discrimination between dark energy and modified gravity
One necessary condition for DE to mimic MG