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

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

Complementarity btw CMB and LSS 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 (e.g., Eisenstein, Hu & Tegmark 98)

Linear growth rate (a case of CDM model) The density perturbation in the LSS, observable from a galaxy survey Linear growth describes 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

CDM Structure Formation Model: P(k) Amplification in the density perturbation amplitude by a factor of 1000, between z=0 and CMB Galaxy Survey k 3 P(k,z)/2  2 ~ R~1/k WL

Massive neutrinos and LSS m tot >0.06 eV m tot >0.06 eV m tot >0.11 eV m tot >0.11 eV 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.

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 Total matter perturbations can grow! CDM < fs > fs Suppresses growth of total matter perturbations

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)

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: FoV: degrees in diameter (~10  the Suprime-Cam’s FoV) broad band filters (BVRiz) available The first light in Plan to conduct a wide-field survey (primarily for WL); hopefully starting from 2011 for 3-5 years

From Y. Komiyama 2 degree FoV option Suprime-Cam

WFMOS (Wide Field Multi-Object Spectrograph) Glazebrook et al. astro-ph/ Echidna Survey area <z<1.3 (n g ~1000deg -2 ), 2.5<z<3.5 (n g ~2000 deg -2 )  ~300 nights Primary science cases: dark energy, neutrinos… Proposed galaxy redshift survey 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 fibers If fully funded (>~$50M): the first-light 2015(?)-, after HSC

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 Gpc 3 –For comparison, SDSS (z~0.3) covers ~1 h -3 Gpc 3 with 4000 deg^2 (Eisenstein etal 05) –V_wfmos ~ 5 V_sdss  _s

Advantage of high-redshift survey (II) At higher redshifts, weaker non-linearities in LSS –A cleaner cosmological info is available up to k max –SDSS: k max ~0.1 h/Mpc –WFMOS z~1: k max ~0.2 h/Mpc z~3: k max ~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

A measurement accuracy of P(k) for WFMOS 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) Neutrino suppress. 0.6% of  _m  ~4% effect on P(k)

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)

Different probes are complementary From Tegmark+04

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!)

Suppression in P(k) Suppression in P(k) 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 P i (k) All P(k) have same amount suppression on sufficiently large k. WFMOS z~3 slice f =0.05 (  =0.014) f =0.01 (  =0.003)

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

WFMOS Can Measure DE Clustering? Another important consequence of DE with w  -1 is its spatial clustering,  de (x,t) A useful way: explore fluid properties of DE (  de,  p de,  de,… ), instead of modeling a form of DE Lagrangian Sound speed c e (  p de ) 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) (MT 06 soon)

Effect on P(k)

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).

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 (~2000deg 2, 4 or 5 colors, n g ~0.3/arcmin 2 or n g ~5  h 3 Mpc -3 ) seems optimal for joint BAO and WL experiments. Valued Sciences: WFMOS can do –Neutrino Mass: sigma(m tot )=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?