Subaru Galaxy Surveys: Subaru Galaxy Surveys: Hyper-Suprime Cam & WFMOSHyper-Suprime Cam & WFMOS

(As an introduction of next talk by (As an introduction of next talk by Shun SaitoShun Saito))

Masahiro Takada

(Tohoku Univ., Sendai, Japan)

Sep 11 07 @ Sendai

CMB + Large-Scale Structure (LSS)CMB + Large-Scale Structure (LSS)

+

WMAP (z~10^3)

LSS (0<z<3)

SDSS (Tegmark etal03)

Complementarity btw CMB and LSSComplementarity 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 secur

e, can be compared with the measurements• A galaxy survey probes the density perturbations at low redshift

s (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)Linear growth rate (a case of CDM model)

€

δ(x;z) ≡ρ(x;z) − ρ (z)

ρ (z)

€

˙ ̇ δ k + 2H ˙ δ k − 4πGρ mδk = 0

• 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 l

eads 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)CDM Structure Formation Model: P(k)

Amplification in the density perturbation amplitude by a factor of 1000, between z=0 and 1000.CMB

Galaxy Survey

k3 P(k

,z)/

22 ~

<δ2

>R

~1/k

WL

Massive neutrinos and LSSMassive neutrinos and LSS

mmttotot>0.06 eV>0.06 eV mmttotot>0.11 eV>0.11 eV

€

Ωm = Ωcdm + Ωbaryon + Ων : fν ≡ ΩνΩm

> 0.005

• 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.

€

1+ znr ≈1890 mν 1eV( )

Suppression in growth of LSSSuppression in growth of LSS• Neutrinos are very light compared to CDM/baryon: the free-stre

aming 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, δ=0, therefore weaker gravitational force compared to a pure CDM case

)(xδ

Total matter perturbations can grow!

CDM CDM

< fs > fs

Suppresses growth of total matter perturbations

€

fs(z) ≈ vν H−1a−1 ⇒ kfs(z) ≈0.68

(1+ z)1/ 2

mν

1eV

⎛

⎝ ⎜

⎞

⎠ ⎟Ωm

1/ 2h Mpc−1

€

˙ ̇ δ + 2H ˙ δ − 4πGρ m (1− fν )δ = 0

Suppression of growth rate (contd.)Suppression of growth rate (contd.)

Suppression of growth rate (contd.)Suppression of growth rate (contd.)12/12,1/2-

fs,i Mpc)(eV1

z)0.68(1)( −Ω⎟⎟⎠

⎞⎜⎜⎝

⎛+≈ h

mzk m

i

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)

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Hyper Suprime-Cam (HSC)Hyper Suprime-Cam (HSC)• Replace the Subaru prime focus cam

era 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

From Y. Komiyama 2 degree FoV option

Suprime-Cam

WFMOS (Wide Field Multi-Object Spectrograph)WFMOS (Wide Field Multi-Object Spectrograph)

Glazebrook et al. astro-ph/0507457

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…

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

• 2000-4000 fibers

• If fully funded (>~$50M): the first-light 2015(?)-, after HSC

Advantage of high-redshift survey (I)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 av

ailable 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

Ω_s

Advantage of high-redshift survey (II)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_sV(k)]

Springel etal. 2005, Nature

€

WFMOS2 (lnP) ~ 0.01σ SDSS

2 (lnP)

A measurement accuracy of P(k) for WFMOSA 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 Ω_m~4% effect on P(k)

The parameter degeneracy in 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)

€

Pprimord (k)∝k

k0

⎛

⎝ ⎜

⎞

⎠ ⎟

n _ s+(1/ 2)α ln(k / k0 )

k0 = 0.002 Mpc-1

Different probes are complementaryDifferent probes are complementary

From Tegmark+04

SummarySummary • CMB+LSS opens up a new window of constraining th

e 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 Suppression in P(k)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 Pi(k)

• All P(k) have same amount suppression on sufficiently large k.

WFMOS z~3 slice

f=0.05 (Ω=0.014)

f=0.01 (Ω=0.003)

Forecasted erroForecasted errors for neutrino rs for neutrino

parasparas• 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

WFMOS Can Measure DE Clustering?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 (δde, δpde, d

e,… ), instead of modeling a form of DE Lagrangian

• Sound speed ce (δpde) 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 (δde=0)

dedemm δδδ +=t

aaH

cdaa ea

)()(

0de ∫=

mmδδ ≈t

(MT 06 soon)

Effect on Effect on PP(k)(k)

Sensitivity of WFMOS to DE perterbatSensitivity of WFMOS to DE perterbationsions

• 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).

SummarySummary• Hyper-Suprime/WFMOS survey will provide an ultimate, i

deal 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 samp

le of WFMOS sample

• Current survey design (~2000deg2, 4 or 5 colors, ng~0.3/arcmin2 or ng~510-4 h3 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 str

ategy?