Baryon Acoustic Oscillations

1. 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

2. Contents Baryon acoustic oscillation and cosmology BAO measurement with WFMOS Activity of Japan BAO theory group

3. Baryon Acoustic Oscillation (BAO) • Acoustic oscillations of primeval baryon-photon fluid • imprinted on the clustering of large-scale structure Typical size z • 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

4. Observations of BAOs Percival et al. (2007) Eisenstein et al.(2005)

5. Physics of BAOs ~brief sketch~ Before the time of decoupling, the Universe was in the plasma state, and photons and baryons (electron) weretightly coupled via Thomson scattering After the decoupling, acoustic patterns of photon and baryon density fields were frozen, and baryon density field has evolved with dark matter under the influence of gravity After decoupling, Before decoupling, Baryon-photons fluid baryon （electron） photon baryon photon Acoustic mode Thomson scattering sound velocity CDM CDM Gravitational growth Gravitational growth ~380,000 year after the Big-Bang BAO was imprinted around the time of decoupling of photons from matter

6. Characteristic Scale of BAOs Sound horizon scale at the time of decoupling (c.f. type Ia SNe ) • Physics of BAOs is well-known, unambiguous • 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

7. Measuring Expansion History Using BAO scale as standard ruler, cosmological distance of high-z objects can be measured H(z) DA(z) redshift Constraints on expansion history Nature of dark energy DA(z) and H(z) can be also used for tests ofgeneral relativity andCopernican principle Angular diameter distance Redshift z In addition, Hubble parameter of distant objects, H(z), can be measured through Alcock & Paczynski effect.

8. Future BAO Measurement Narrowing constraints on dark energy A percent-level determination of H(z) & DA(z) : SDSS LRG: Minimal requirement 2dF GRS: Planned WFMOS survey (z~1 & 3) satisfies this requirement, and c.f. is complementary to other BAO experiments (BOSS, HETDEX, …)

9. 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 small, but non-negligible effects at percent level Galaxy biasing Development of theoretical modeling and feasibility study for precision measurement

10. Japan BAO Theory Group (friends ?) IPMU I.Kayo, M.Takada, N.Yoshida 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 !!

11. 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.

12. 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.

13. x(r) z=0.5 1 2 z=3 Modeling Non-linear Evolution Real space P(k)/Psmooth(k)

14. Modeling Non-linear Evolution Redshift space (monopole) x(r) z=0.5 P(k)/Psmooth(k) 1 2 z=3

15. 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)

16. 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 • Measurement of BAOs leads to Simultaneous determination of (~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.