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 on ZPJ, Michele Liguori, Rachel Bean & Scott Dodelson, 2007, PRL ZPJ & Xuelei Chen, 2008, PRD Bhuvnesh Jain & ZPJ, 2008, PRD - PowerPoint PPT Presentation
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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
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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!!
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• 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
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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
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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
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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
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)()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
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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
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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)
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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
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Testing the consistency relation through spectroscopic redshift surveys
Acquaviva et al. 2008
=0 in GR+smooth dark energy
BAO+CMB
Redshift distortion
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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
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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)