PFS Deep SurveyforGalaxy Formation and Cosmic Reionization
Masami Ouchi (Tokyo),Kazuhiro Shimasaku (Tokyo),
Yen-Ting Lin (IPMU) et al.

Prime Focus Spectrograph (PFS)FoV of Suprime

FoV of FOCAS
Obs. area x200

Obs. area x7

FoV of PFS

Multiplicity x100

~1.5 degFoV of HSC

TMT/WFOSDEIMOSVIMOS Suprime-Cam→HSC (obs. area x7) from 2011 FOCAS→PFS (obs. area x200, multiplicity x100) from 2016?-

Complementary to the other 8m-telescope and ELT spectrographs→PFS could revolutionalize spec. studies of highz galaxies reachable with>8m telescopes. No competing studies.

Magnitude limit surveys do not reachgalaxies up to z~7mag
N(1FoV) Exp(total;hr) mz< 23.076000
10 mz=23.0-23.5 32000
11 mz=23.5-24.0 45000
42 mz=24.0-24.5 64000 128
total
191(hr)For 1 FoV(WFMOS) ~ 30nights (for 2008 WFMOS Kona meeting)
The brightest z~7 galaxy in 0.5 deg^2 have m~25.5(Ouchi et al. 2009)
Targeting color selected galaxies for high redshiftsPerfect Targets Supplied fromHSC Deep/Ultra-Deep surveys (Japan-Princeton-Taiwan)

Suprime-Cam

Hyper SuprimeCam(HSC;2011-)

N=207

140 Mpc

Present largest obs.
(Ouchi+10) 1/30

~6 deg: ~0.5-0.9 comoving Gpc at z~2-7•

Current model(Mesinger+09)

High-z galaxies: Lyman break galaxies (LBGs) and Lya emitters (LAEs). Brightin optical bands→ Ideal for PFS optical spectroscopy. Nearly ‘complete’
spectroscopy down to a given UV-continuum magnitude or Lya flux.

Candidates from HSC(being designed)
Lyman break galaxies(LBGs)

Lya Emitters (LAEs)

x10-100
x10-100
Previous studies(incl. Suprime results)• Tentative plans

Expected numbers of high-z galaxies (Ouchi+)– Deep survey (i~27mag, NB~25mag) for ~30deg2– Ultra deep survey (i~28mag, NB~26mag) for ~3.5deg2→10k-1M LBGs and 1k-10k LAEs at z=2-7. # of galaxy
candidates is boosted by 10-100x.

• 10-100 times more spec. targets will be waiting forspectroscopy. Large enough for PFS spectroscopy.

Deep PFS Surveys
Four Science Drivers (TBD)
1. Mass assembly of massive galaxies.
What is the major process, accretion ormergers? Is stellar (or dark mass)assembly first?
2. Chemical and dynamical evolution of
intense star-forming galaxies
3. Galaxy, AGN, and proto-cluster formationin large scale structure at early stage
4. Cosmic reionization probed with galaxies

1) Mass Assembly of Massive Galaxies
Mergers or cold accretion?

Dekel et al. (2009)• Violent SF at z>2, but mostly no merger signatures• Galaxies acquired most of baryon (~70%!) at z~2-3 via
cold accretion (e.g. Katz+03, Keres+09, Dekel+09) ?
• Is this true? Any observational signatures?

Testing Cold Accretion Hypothesis
Low ionization IS metal absorption
vsys from Hα••Faucher-Giguere+10
Steidel+10
No signature of cold gas accretion, but outflow based on 89 LBGs at z~2,
(Steidel et al. 2010).
But, consistent with cold accretion models, because a covering factor of cold
accretion gas is very small ~1-2%(Faucher-Giguere+10), and a signal can beobtained when a cold filament is exactly aligned with the line of sight, Kimm+10).→need very large optical+NIR spectroscopic sample of LBGs1) Targeting LBGs at z=2.1-2.4
Sweet Spot of PFS Galaxy Survey• Three channels; Blue(3800-6700A), Red(6500-10000A), andIR(10000-13000A)• Blue+IR channels→ UV spectra (Lya, IS absorption lines) and[OII] lines for LBGs at z=2.1-2.4.
1. Absorption lines in UV cont and Lya → inflow/outflow indicators
2. [OII] lines→ systemic velocities
Signature of cold accretion and/or constraints on a covering factorof accretion gas with a 10-100x larger sample than prev. study

Major Mergers
Driving mechanism of galaxy evolution in hierarchical structure formation
Relates to starburst, AGN activity, formation of early-type galaxies
Few measurements at z>1 using close pairs(eg, Ryan+08, Bluck+09, Cooke+10)
very small statistics
mostly based on phot-z
cf. method using morphology
is complementary but hasa limitation

Study with PFS

Ryan+08

Cooke+10

Identify physically associated close pairs from large LBG+LAE
samples. (Exploiting the positive correlation of stellar-mass and UV
luminosity, e.g. Papovich+01,Yabe+09)- N~1000 close pairs with spec-z- merger fraction at different z, SFR, stellar mass

Dark mass assembly: connectingstars (baryon) and dark halos

z=4 LBG correlation function fit by
HOD model (Ouchi+06,Hamana+06)

z=4 Mass-luminosity relation by conditional
luminosity func. model (Cooray&Ouchi 06)• Precision measurements of LF and CF– Largest uncertainties→ sample contamination and N(z)– Constraining star-forming galaxies with numerical simulation, halo
occupation distribution (HODs) and conditional luminosity func. models

Star-Formation Duty Cycle(intermittent SF history for stellar-mass buildup?)
LAEs only

Duty cycle

Sheth&Tormen(1999) model

Ouchi et al. (2010)•••Precision measurements of high-z galaxy luminosity function and correlation function.→hosting halo mass+HOD+duty cycle (Ouchi et al. 2004, Lee et al. 2009, Ouchi et al. 2010)
Halo mass determination (just an accuracy of an order-a factor of ~5)
Duty cycle of dropout and Lya emitting population is ~10% and ~1%, respectively (just anaccuracy of an order). Constraints on SF history and Lya production mechanism.

2) Constraints on Metallicity at z~2-6
with Metal Absorption Lines?
Ando et al. (2007)• Metallicity estimated from low-ionization IS lines (Heckmanet al. 1998), CIV-index (Mehlert et al. 2003) etc.
• Composite spectra of very faint LBGs→ metallicity of very
faint/less-massive galaxies (~300 m telescope science)• Complementary to ELT(z<2-4) and JWST(bright) studies

2) Do z~2-7 Galaxies include PopIII starbursts?

No detection

z=3.1(Ouchi+08)
PFSOuchi+08••

HeII is an indicator of forming galaxies (ionized by massive stars).
Composite spectra→no HeII emission (no signature of popIII/cooling radiation)–••

Hardness of flux expressed by
the ratio of He+ to H ionising flux(Schaerer 2003)

3σ upper limits: f(Hell)/f(Lya)< 2% at z=3.13 (Ouchi et al. 2008)

No signatures of popIII SF.
PFS observations for 10k high-z galaxies→ identifying popIII SB comp. with a top heavy IMF.

3) Large-scale structuresand proto-clusters
at z>4

Ouchi et al.
2005

5σ-level excess

PFS FoV•concentration B

z=5.7±0.05

N=401•

concentration Awhite circles=No spec-z

Searching for large-scale structures and proto-clusters in a volume 100 x
larger than the previous Subaru surveys. (cf. the filamentary LSSs+protocluster at z~3-6 Shimasaku+03, Hayashino+04, Ouchi et al. 2005). (100 proto-clusters at z~5-6)
3D maps of high-z universe for charting large scale structures4) Cosmic Reionization
Tight Relation with Galaxy Formation
Reionization

Ionized IGM(orange),
neutral IGM(green), andGalaxies (blue)

Ly-continuum photons
to ionize the universe

Intense UV backgroundto suppress dwarf-galaxyformation

Galaxy formation

M(halo)=6e7 Mo M(halo)=6e8 Mo
z_c=1.7z_c=7.6
Susa & Umemura+04

Open Questions (1)Evolution of Neutral Hydrogen Fraction
WMAP7?

Choudhury+08 models
Mh(lim)~1098Mo
Mh(lim)~10 Mo
Mh(lim)~106Mo

LinearPlot

Ouchi et al. (2010)

Log Plot– z~6: QSO Gunn-Peterson test
– z~11: CMB Thomson scattering optical depth
sharp reionization or extended reionization (Dunkley+09)? ? Is significant minihalo(Mh~106Mo) contribution (Choudhury+08) required??

Open Questions (2)Ionization process
Inside-out? Outside-in?

Or filament-last?

Finlator+09– The ionization process: How did the ionized regions extend?
• Depending on distribution of ionizing sources and IGM density• Inside-out (e.g. Furlanetto et al. 2004), outside-in (e.g. MiraldaEscude et al. 2000), or filament-last (Finlator et al. 2009).

Not enough S/N with the present 21cm-obs facilities such as
LOFAR

Reionization and Physical Processes
Filament-last reionization?
IGM

PFS+HSC survey

LAE(int)?
LAE(obs)
McQuinn+07

Finlator+09– Physical processes from topology (inside-out,outside-in, filament-last?)– Clustering of Lya emitters: imprints of neutral fraction andionized bubble topology（McQuinn et al. 2007)

Constraints So Far Obtained

Ouchi et al. (2010)– The clustering of Lya emitters at z~7 is not well constrained with the present
Subaru studies, due to small statistics. （phot.sample~200, spec.sample~30 at z=6.6)→xHI<~0.5 at z=6.6. None for the ionized bubble topology• PFS+HSC→~100 x larger sample（~10k LAEs）→xHI and topology
PFS: Composites of Lya line profiles in a few 10Mpc area. Spatial varianceof line broadening/Lya-FWHM relation for reionization test.

Bright-end LF determination
For Budget of Ionizing Photons
Ionizing Photon Budget•

Ouchi+09b
Ouchi+09b
At z~7, did galaxies produce ionizing photons
enough for ionizing the hydrogen IGM?
––Bouwens+10•

Galaxies alone may not reionize the universe
orUniverse is already ionized by galaxies, butthese galaxies have higher escape fraction[>0.2],(lower metallicity top-heavy IMF) or undetectedfaint galaxy population (α<~-1.9?).

The determination of α with PFS+HSC data,
HUDF, and the forthcoming CANDLES data.

OBSERVATIONS AND
REQUIREMENTSPFS Observations(TBD)

 PFS 12 hour (6hour each)
integration/pos. for 30 deg^2

L*Covering HSC DS area (30deg^2): ~60 nights incl.
overhead+weather with PFS
Goals: logL>42.7-42.8 erg/s; 6000 LAEs atz=5.7-6.6 and >10000 LBGs+LAEs at z=2-7

Required PFS Performance• Faint limits of PFS performance, this survey requires
good→ high sensitivities with good sky subtraction.
The high throughput (10-20%) is indispensable.
Moreover, for good sky subtraction and less smearingof signals, we request a stability of spectrographideally as high as Keck/LRIS and DEIMOS.
• A half of sensitivity → twice of Subaru nights (orprobably more, due to the systematics)• Fiber diameter should be optimized. High S/N
for a point source is desirable.

SummaryPFS Deep Survey for Galaxies at z=2-7
Spectroscopic follow-up of ~30 deg^2 HSC D/UD fields
1. Mass assembly of massive galaxies. (Cold accretionor mergers?)
2. Chemical and dynamical evolution of intense starforming galaxies
3. Galaxy, AGN, and proto-cluster formation in large
scale structure at early stage
4. Cosmic reionization probed with galaxies
Required nights (~60-120 nights; TBD)
Required performance→high sensitivity (incl. stability)