Yutaka Komiya (National Astronomical Observatory

of Japan)Takuma Suda (NAOJ),

Masayuki Y. Fujimoto (Hokkai Gakuen Univ.)

Extremely metal-poor (EMP) stars = “living fossils” in the local group

Observation : ~ 1,000 stars with [Fe/H]<-2.5 is identified in the Milky Way (MW) halo Database: SAGA (Stellar Abundance for Galactic Archaeology, see Suda-san’s

poater) 2nd generation stars

chemical signature of Pop. III supernovae (SN)

Were low mass Pop. III stars formed ? Pop. III star cluster : Clark+ (2008, 2011), Greif+ (2011), Susa+ (2012) Pop. III binary : Machida+ (2008), Turk+ (2009), Stacy+ (2010)

⇒Pop. III survivors

Pop. III survivors Where are they ? What they looks like ? How can we observe them ?

Method Hierarchical chemical evolution model

based on the concordance cosmology Merging history of the Milky Way (semi-analytic) Gas outflow, circumgalactic matter Surface pollution of stars by the accretion of interstellar matter.

Pop. III survivors In the MW halo

Surface abundance Outside the MW

Escape fraction Spatial distribution, Detection probability

（ 2nd generation stars ） Metallicity distribution Chemical signature of Pop. III stars (PISN)

Merger tree: Somerville & K (1999) MMW=1012 M☉, Mmin=M(Tvir=103K)

Gas infall (merger tree), outflow (SN) All the individual EMP stars are registered in

computations Constant star formation efficiency : 1×10-10/yr Instantaneous mixing inside mini-halos. Yield : Kobayashi et al.(2006, Type II SN)

Nomoto et al. (1984, Type Ia SN) Umeda & Nomoto (2002, PISN)

Mini-halo~106M☉

Milky Way

Proto-galaxy

First star

First supernova

redshift

mass

Lognormal IMF ξ(log m) = exp( -log(m/Mmd)2/σ ２ ) Mmd=10Mʘ, σ=0.4 (Pop. II)

(Komiya et al. 2007)

Binary Binary fraction: 50% Mass ratio distribution: n(q) = 1

Pop. III IMF Fiducial model: Mmd = 200Mʘ (Pop. III.1), Mmd =

40Mʘ (Pop. III.2), Zcr = 10-6Zʘ

A little low mass Pop. III stars are formed. Parameter dependence

PrimarySecondar

y

22

2

22

2s

s

cvcv

Gmm

EMP star

Data from SAGA(Suda et al. 2008, 2010)http://saga.sci.hokudai.ac.jp

Gray histogram: HES survey (Schöerck+ 2009)Black line : SAGA sample

「

[Mg/Fe]

[Ba/Fe]

Rp-rpcess source: 8 – 10 Mʘ

~ 800 Poop. III survivors

In the Milky Way halo Their surface abundance is changed by the accretion of

interstellar medium (ISM) ⇒ Observed as Z ≠ 0

How much are they polluted ?

Outside the Milky Way Some Pop. III stars are escaped from mini-halo

when their primary companion explode (3 body interaction in star cluster )

Remains with Z=0

binarySN explosion Secondary

star go away

In the Milky Way halo Metallicity, chemical abundance

[Fe/H] ~ －５

（ C, N, s-process: binary mass transfer ）

⇒ Observed as Hyper Metal Poor stars.

object [Fe/H] [C/Fe]HE0107-5240: -5.4 +3.7HE1327-2326: -5.7 +4.16HE0557-4840: -4.8 +1.65SDSSJ102915+172927: -4.89 <0.93

~ 800 Poop. III survivors.

In the Milky Way halo Their surface is polluted by the accretion of interstellar

medium (ISM) ⇒ Observed as Z ≠ 0

How much are they polluted ?

Outside the Milky Way Some Pop. III stars are escaped from mini-halo

when their primary companion explode (3 body interaction in star cluster )

Remains with Z=0

binarySN explosion Secondary

star go away

Outside the Milky Way Escape frequency

(We assume that the distribution of the orbital parameters of Pop. III binaries is the same as the solar vicinity )

From mini-halos with 106Mʘ, 20 % of low-mass Pop. III stars go out.

Preliminary

Outside the Milky Way Spatial distribution

Preliminary

2 – 3 Mpc 1Mpc 3Mpc

100 – 170 Pop. III stars 1000 – 1800 EMP stars ([Fe/H]< -2.5)

300kpc

10 merger trees

Detection probability Giant

V ~ 26 mag @ 1Mpc (Subaru Strategic Program, i<26 mag, u,g,r,I,z band,

1,400 deg^2 by 5 yrs, ) Discrimination

Narrow band filter ? Spectroscopic follow-up

Main sequence, Turn-off star ⇒ very difficult

Evidence of the Hierarchical Galaxy Formation Constrain the Dark-halo Mass of the First Galaxy

Preliminary

Hierarchical chemical evolution model Surface pollution Metal enrichment of circum-galactic matter

Pop. III survivors In the Milky Way halo

⇒ observed as HMP stars by the surface pollution

Outside the Milky Way halo remained with Z=0

~100 Pop. III survivors, 2 – 3 Mpc can be observed by Subaru Hyper Suprime-Cam

(?)

IMF of Pop.III Mmd=10Mʘ

Minimum halo mass Tvir > 104 K

MDF

Chemical signature

Parameter dependenceMmd(Pop.III.1) = 40Mʘ

Mmd(Pop.III.1) = 10Mʘ

Zcr = 10-4Zʘ

Low mass Pop. III stars Cluster :

Clark+ (2008, 2011) Greif+ (2011) Susa+ (2012) …

Binary (multiple system) ： Machida+ (2008) Turk+ (2009) Stacy+ (2010) …

How and where can we observe Pop. III survivors ?

Greif+ (2011)

Machida+ (2008)

Ek: SN kinetic energy = 0.1*Eexp

Ebin: Binding energy of a proto-glaxy ε(=0.1): minimum outflow energy rateMsw: mass swept up by a SN shell

Mini halo

First SN

SN ejecta

Pre-enriched mini halo

Gas blowout (SN driven wind)•Energy injection :

•Mass loading :

•Metal loading :

Evolution of galactic wind in the CGM•momentum conservation snowplow of th spherical shell

IMF: Lognrmal IMF, Mmd=200Mʘ (Pop. III.1), Mmd=40Mʘ (Pop.III.2) Binary fraction: 50% Mass ratio distribution: n(q)=1

Binary orbit Period: Duquennoy & Mayer (1991)

Eccentricity: e=1

Remnant mass of massive stars Woosley (2002)

Mini-halo NFW density profile Stars are formed at the center of mini-halo

Escape criterion

22

log 4.8log ( ) exp

2 2.3

Pf P day

tmerge

Main haloMass: Mmh(t)

Merger tree

Initial distance: estimated from merger tree. We assume that, distance of mini-halo which accrete to main halo with mass M at tmerge

= radius of a spherical shell with M which collapse at tmerge

We computed distance and radial velocity of mini-halos as a function of tmerge and Mmh(tmerge). Where tmerge is a age when the mini-halo accrete to the main halo and Mmh(tmerge) is the mass of main halo at the merger.

d2r/dt2 = -GM/r2 + Λc2r/3

time

Universe

d2r/dt2 = -GM/r2 + Λc2r/3

Main halo

rinit

Angle Θ (random)

Mini halo

vinit

d2r/dt2 = -G(Mmain(t)+4πρavr(t)3/3)/r2 + Λc2r/3 + l2/r3

l = r(tform)vescsinθ

In the Milky Way haloHyper metal poor stars = Pop. III survivors ?

object [Fe/H] [C/Fe]HE0107-5240: -5.4 +3.7HE1327-2326: -5.7 +4.16HE0557-4840: -4.8 +1.65SDSSJ102915+172927: -4.7 <0.93

Fe: accretion of ISMC, N. Mg.. : binary mass transfer

PISN ? (~200 Mʘ) Low [Zn/Fe] High [Si/Fe], [Ca/Fe] Odd even effect

Type II ? (10 – 50 Mʘ) (typical abundance of the halo stars)

Hypernovae ? ( 20 – 50 Mʘ) Large [Zn/Fe]

(Fast rotating star ?) (Supermassive star ?)

Umeda & Nomoto (2002)

Mass ratio Sana & Evans 2010

Raghavan et al. 2010

In the Milky Way halo Formation epoch

Formation redshift of low mass EMP stars (red) and Pop.III stars (green) .

Metal enrichment history of the CGM