Masahiro Takada (Tohoku Univ., Sendai, Japan)

1. Subaru Galaxy Surveys: Hyper-Suprime Cam & WFMOS(As an introduction of next talk by Shun Saito) Masahiro Takada (Tohoku Univ., Sendai, Japan) Sep 11 07 @ Sendai

2. CMB + Large-Scale Structure (LSS) + WMAP (z~10^3) SDSS (Tegmark etal03) LSS (0<z<3)

3. Complementarity btw CMB and LSS (e.g., Eisenstein, Hu & Tegmark 98) • CMB probes the statistical properties of fluctuations at z~10^3 • All the fluctuations are well in the linear regime: clean info • Linear perturbation theory predictions, which are robust and secure, can be compared with the measurements • A galaxy survey probes the density perturbations at low redshifts (0<z<3) • The perturbation amplitudes significantly grow from z~10^3, by a factor of 10^3 at least • An uncertainty in the model predictions arises from non-linearities in structure formation • Combining the two is very powerful (e.g., WMAP + SDSS) • Opens up a window to probe redshift evolution of the perturbations, which helps break parameter degeneracies • Allow to constrain the neutrino mass • Very complementary in redshift and wavenumbers probed

4. The density perturbation in the LSS, observable from a galaxy survey Linear growthdescribes the time-evolution of the density perturbations, form the CMB epoch (z~10^3) In the matter-dominated regime, the CDM perturbations of different wavelengths grow at the same rate Combining the FRW eqns and the linearized GR+Boltzmann eqns leads to the second-order differential equation Alternative, yet interesting ingredients The cosmic acceleration slows down the growth Adding massive neutrinos leads to suppression in the growth at low redshifts and on small scales Linear growth rate (a case of CDM model)

5. WL Galaxy Survey CMB CDM Structure Formation Model: P(k) k3P(k,z)/22~<2>R~1/k Amplification in the density perturbation amplitude by a factor of 1000, between z=0 and 1000.

6. Massive neutrinos and LSS • The experiments imply the total mass, m_tot>0.06 eV • Neutrinos became non-relativistic at redshift when T,dec~m • Since then the neutrinos contribute to the energy density of matter, affecting the Hubble expansion rate • The cosmological probes (CMB, SNe, BAO …) measure • The massive neutrinos affect the CMB spectra, mainly through the effect on H(z) (see Ichikawa san’s talk) • The effect is generally small, also degenerate with other cosmo paras. mtot>0.11 eV mtot>0.06 eV

7. Suppression in growth of LSS • Neutrinos are very light compared to CDM/baryon: the free-streaming scale is ~100Mpc (for m~0.1eV), relevant for LSS • At a redshift z • The neutrinos slow down the growth of total matter pert. • On large scales >fs, the neutrinos can grow together with CDM • On small scales <fs, the neutrinos are smooth, =0, therefore weaker gravitational force compared to a pure CDM case  < fs  > fs CDM CDM Suppresses growth of total matter perturbations Total matter perturbations can grow!

8. Suppression of growth rate (contd.)

9. Suppression of growth rate (contd.) k_fs The suppression is stronger at lower redshifts, implying the usefulness of CMB+LSS to probe the neutrino effect E.g., the current limit on the total neutrino mass, m_tot<0.9 eV (95%) from WMAP +SDSS (Tegmark etal. 06)

10. Hyper Suprime-Cam (HSC) • Replace the Subaru prime focus camera with the new one (HSC) • PI: S. Miyazaki (NAOJ) • The grant (~$15M) to build the new camera was approved in 2006 • Construction: 2006-2011 • FoV: 1.5 - 2.0 degrees in diameter (~10  the Suprime-Cam’s FoV) • 4 - 5 broad band filters (BVRiz) available • The first light in 2010 - 2011 • Plan to conduct a wide-field survey (primarily for WL); hopefully starting from 2011 for 3-5 years

11. Suprime-Cam From Y. Komiyama 2 degree FoV option

12. WFMOS (Wide Field Multi-Object Spectrograph) • The project originally proposed by Gemini observatory (US+Europe+) to Japan (2005-) • Now seriously considered as a next-generation Subaru instrument: in the phase of the feasibility/design study • Assume the HSC FoV • 2000-4000 fibers • If fully funded (>~$50M): the first-light 2015(?)-, after HSC Echidna • Survey area 2000 deg^2 @ 0.5<z<1.3 (ng~1000deg-2), 300deg^2 @ 2.5<z<3.5 (ng~2000 deg-2)  ~300 nights • Primary science cases: dark energy, neutrinos… Glazebrook et al. astro-ph/0507457 Proposed galaxy redshift survey

13. Advantage of high-redshift survey (I) • For a fixed solid angle, a higher-redshift survey allows to cover a larger 3D comoving volume • A more accurate measurement of P(k) is available with a larger surveyed volume • A planned WFMOS (z~1 survey with 2000 deg^2 + z~3 survey 300 deg^2) • ~4 (z~1) + ~1 (z~3) = ~5 h-3 Gpc3 • For comparison, SDSS (z~0.3) covers ~1 h-3 Gpc3 with 4000 deg^2 (Eisenstein etal 05) • V_wfmos ~ 5 V_sdss _s

14. Advantage of high-redshift survey (II) • At higher redshifts, weaker non-linearities in LSS • A cleaner cosmological info is available up to kmax • SDSS: kmax~0.1 h/Mpc • WFMOS • z~1: kmax~0.2 h/Mpc • z~3: kmax~0.5 h/Mpc • Surveyed volume in F.S. • V_wfmos(k)~30V_sdss(k) • In total, accuracy of measuring P(k): 2(lnP(k))~1/[V_sV(k)] Springel etal. 2005, Nature

15. A measurement accuracy of P(k) for WFMOS Neutrino suppress. 0.6% of _m ~4% effect on P(k) • WFMOS allows a high-precision measurement of P(k) • The characteristic scale-dependent suppression in the power of P(k) due to the neutrinos could be accurately measured (see Saito kun’s talk)

16. The parameter degeneracy in P(k) • Different paras affect P(k) in fairly different ways • Combining galaxy survey with CMB is an efficient way to break degeneracies btw f_nu, n_s and alpha (MT, Komatsu & Futamase 2005)

17. Different probes are complementary From Tegmark+04

18. Summary • CMB+LSS opens up a new window of constraining the neutrino mass, from the measured suppression in the growth of mass clustering • A higher redshift survey, such as the survey of planned Subaru survey, allows a precise measurement of the galaxy power spectrum • Need to develop more accurate theoretical predictions of P(k) for a mixed DM model that allow a secture comparison with the precise measurement (see Saito kun’s talk!)

19. Suppression in P(k) f=0.05 (=0.014) • Assume 3 flavors when relativistic • Consistent with CMB and BBN • Assume N species become NR (or are massive) at low-z • Suppression has scale-dependence • P(k) amplitude is normalized by the primordial Pi(k) • All P(k) have same amount suppression on sufficiently large k. WFMOS z~3 slice f=0.01 (=0.003)

20. Forecasted errors for neutrino paras • 2D galaxy P(k) is very powerful to constrain mtot • N.O. experiment neutrinos can be weighed at more than 1: (mtot)=0.03eV • Relatively difficult to constrain N and mtot independently. • If mtot>0.45eV, models with N=1 can be discriminated at more than 1-sigma level

21. WFMOS Can Measure DE Clustering? (MT 06 soon) • Another important consequence of DE with w-1 is its spatial clustering, de(x,t) • A useful way: explore fluid properties of DE (de, pde, de,… ), instead of modeling a form of DE Lagrangian • Sound speed ce (pde) defines the free-streaming scale of DE clustering (e.g., quintessence, c_e=1) • > fs : DE can cluster with DM •  < fs : DE perturbations are smooth (de=0)

22. Effect on P(k)

23. Sensitivity of WFMOS to DE perterbations • If c_e<0.1, WFMOS can measure the DE perturbations at more than 1-sigma significance. • The power is compatible with an all-sky imaging survey (CMB-galaxy cross-correlation, Hu & Scranton 04).

24. Summary • Hyper-Suprime/WFMOS survey will provide an ultimate, ideal dataset for performing BAO as well as WL tomography experiments. • BAO and WL are complementary for DE constraints, and more important is the independent two methods from the same surveyed region will be very powerful to test various systematics. • Issue for WL: Need to study which type of galaxies gives a fair sample of WFMOS sample • Current survey design (~2000deg2, 4 or 5 colors, ng~0.3/arcmin2 or ng~510-4h3 Mpc-3) seems optimal for joint BAO and WL experiments. • Valued Sciences: WFMOS can do • Neutrino Mass: sigma(mtot)=0.03eV • Dark energy clustering • In this case, z<1 survey is crucial for doing this (z~3 survey can’t do) • Inflation parameters (ns and alpha): ~10^-3 • Having a well-defined survey geometry is crucial: optimal survey strategy?