2009/01/14
すばるユーザーズミーティング
@天文台
Baryon Acoustic Oscillations
Atsushi Taruya
(RESCEU, Univ.Tokyo)
RESCEU=RESearch Center for the Early Universe
Contents
Baryon acoustic oscillation and cosmology
BAO measurement with WFMOS
Activity of Japan BAO theory group
Baryon Acoustic Oscillation (BAO)
 Acoustic oscillations of primeval baryon-photon fluid
imprinted on the clustering of large-scale structure
Typical
size
 Detection & Observation of BAOs:
SDSS main, LRG samples
2dF GRS
Eisenstein et al. 2005; Cole et al.2005; Hutsui 2006; Percival et al. 2007;
Okumura et al. 2008; Cabre et al. 2008; Gaztanaga et al. 2008
Observations of BAOs
4.7 104 galaxies
Eisenstein et al.(2005)
5.2 105 galaxies
Percival et al. (2007)
Physics of BAOs ~brief sketch~
~380,000 year after the Big-Bang
BAO was imprinted around
the time of decoupling of photons from matter
Before
thedecoupling,
time of decoupling,
the Universe
was inand
the baryon
plasma
After the
acoustic patterns
of photon
state,
and
photons
baryons
(electron)
werefield
tightly
density
fields
were and
frozen,
and baryon
density
hascoupled
evolved
via
Thomson
scattering
with
dark matter
under the influence of gravity
After decoupling,
Before decoupling,
baryon
（electron） Thomson
scattering
Baryon-photons fluid
photon
CDM Gravitational growth
baryonAcoustic mode
photon
c
sound c 
CDMs 3{1  (3 / 4)(  baryon  photon)}
velocity
Gravitational growth
Characteristic Scale of BAOs
Sound horizon scale at the time of decoupling zde  1089:


 

0.25
0.08
dz ' cs ( z ' )
2
2
rs ( zdec )  
 147  m h 0.13
 b h 0.023
Mpc
zdec H ( z ' )
• Physics of BAOs is well-known, unambiguous (c.f. type Ia SNe )
• Insensitive to the presence of dark energy
(Only weakly depends on matter and baryon density parameters)
• There’s no significant disturbances that erase acoustic patterns
BAO scale is a robust standard ruler
Measuring Expansion History
Using BAO scale rs as standard ruler,
cosmological distance of high-z objects can be measured
H(z)
Redshift z
Angular diameter
distance
rs
DA ( z ) 

DA(z)
rs

redshift
rs
Constraints on expansion history
Nature of dark energy
In addition, Hubble parameter
ofH(z)
distant
objects,
H(z),
canofbe
DA(z) and
can be
also used
for tests
measured through Alcock
& Paczynski
effect.
general
relativity
and Copernican principle
Future BAO Measurement
Narrowing constraints on dark energy
w w  3%
dw dz  / dw dz   25%
A percent-level determination of H(z) & DA(z) :
P( k )

P( k )
2
N modes
2


1
k
 ; N modes  2k Vsurvey
1 
 n P( k ) 
2
gal


3
Minimal
requirement
Vsurvey  5 h Gpc
Ngal  2106
SDSS LRG:
3
c.f.
Vsurvey ~ 0.7 h3 Gpc 3
2dF GRS:
Vsurvey ~ 0.1h3 Gpc 3
Planned WFMOS survey (z~1 & 3) satisfies this requirement, and
is complementary to other BAO experiments (BOSS, HETDEX, …)
Toward Precision Measurement
Precision measurement of BAOs needs
accurate theoretical templates for P(k) and x(r)
in order to determine the BAO scale
Systematic effects on BAOs:
Non-linear gravitational evolution
Redshift-space distortion
Galaxy biasing
small, but non-negligible
effects at percent level
Development of theoretical modeling
and feasibility study for precision measurement
Japan BAO Theory Group
IPMU
I.Kayo, M.Takada, N.Yoshida
(friends ?)
Univ. Tokyo
T.Hiramatsu (ICRR), T.Nishimichi, S.Saito, Y.Suto,
A.Taruya
NAOJ
T.Hamana, A.Nishizawa
Nagoya Univ.
T.Matsubara, N.Sugiyama, R.Takahashi
Hiroshima Univ.
H.Nomura, K.Yamamoto
People who are interested in BAO are very welcome !!
Publications
Yamamoto et al. 2006, PRD 74, 063525
Yamamoto et al. 2007, PRD 76, 023504
Nishimichi et al. 2007, PASJ 59, 1049
Matsubara 2008, PRD 77, 063530
Taruya & Hiramatsu 2008, ApJ 674, 617
Saito, Takada & Taruya 2008, PRL 100, 191301
Matsubara 2008, PRD 78, 083519
Takahashi et al. 2008, MNRAS 389, 1675
Nomura, Yamamoto & Nishimichi 2008, JCAP 10, 031
Nishimichi et al. 2009, PASJ, in press (arXiv:0810.0813)
Takahashi et al. 2009, in prep.
Taruya et al. 2009, in prep.
Modeling Non-linear Evolution
• Development of new analytic treatment
based on perturbation theory
• Reduction of numerical systematics in N-bosy simulations
• Check of convergence regime of
N-body simulations and analytic models
Accurate and reliable template for BAOs
(1% precision)
 Error forecast including non-Gaussian error is also developed.
Modeling Non-linear Evolution
P(k)/Psmooth(k)
Real space
x(r)
z=0.5
1
2
z=3
Modeling Non-linear Evolution
Redshift space
(monopole)
P(k)/Psmooth(k)
x(r)
z=0.5
1
2
z=3
Feasibility
0.1
Non-linear
Linear (Idealistic)
Distance
estimation
error
Improved PT
valid
0.01
DD/D
Improved PT
valid
0.001
0
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
kmax [h/Mpc]
Nishimichi et al. (2009)
Summary
Measurement of BAOs with future redshift surveys opens a
new window to probe cosmic expansion history
 Acoustic signature of primeval baryon-photon fluid
can be used as cosmic standard ruler
1
rs ( zdec )  150 h Mpc
 Measurement of BAOs leads to Simultaneous determination
of DA ( z) and H ( z) (~1% precision in WFMOS)
Nature of dark energy (equation-of-state parameter)
Test of general relativity / cosmological principle
Japan BAO theory group seriously considers BAO experiment
with WFMOS. Theoretical tools are now developing.