1. Yutaka Komiya (National Astronomical Observatory of Japan) Takuma Suda (NAOJ), Masayuki Y. Fujimoto (Hokkai Gakuen Univ.)

2.  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)  2 nd 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 ?

3. 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  （ 2 nd generation stars ）  Metallicity distribution  Chemical signature of Pop. III stars (PISN) go out from mini-halo. Mini-halo

4.  Merger tree: Somerville & K (1999) M MW =10 12 M ☉, M min =M(T vir =10 3 K )  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 ~10 6 M ☉ Milky Way Proto-galaxy First star First supernova redshift mass

5.  Lognormal IMF  ξ (log m) = exp( -log(m/M md ) 2 / σ ２ )  M md =10M ʘ, σ =0.4 (Pop. II) (Komiya et al. 2007)  Binary  Binary fraction: 50%  Mass ratio distribution: n(q) = 1  Pop. III IMF  Fiducial model: M md = 200M ʘ (Pop. III.1), M md = 40M ʘ (Pop. III.2), Z cr = 10 -6 Z ʘ  A little low mass Pop. III stars are formed.  Parameter dependence Primary Secondary

6.  EMP star

7. 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 M ʘ

8. ~ 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 binary SN explosion Secondary star go away

9.  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 +3.7 HE1327-2326: -5.7 +4.16 HE0557-4840: -4.8 +1.65 SDSSJ102915+172927 : -4.89 <0.93

10. ~ 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 binary SN explosion Secondary star go away

11.  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 10 6 M ʘ, 20 % of low-mass Pop. III stars go out.  Preliminary

12.  Outside the Milky Way  Spatial distribution Preliminary 2 – 3 Mpc 1Mpc3Mpc 100 – 170 Pop. III stars 1000 – 1800 EMP stars ([Fe/H]< -2.5) 300kpc 10 merger trees

13.  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

14.  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 (?)

15. IMF of Pop.III M md =10M ʘ Minimum halo mass T vir > 10 4 K

16.  MDF

17.  Chemical signature

18.  Parameter dependence M md (Pop.III.1) = 40M ʘ M md (Pop.III.1) = 10M ʘ Z cr = 10 -4 Z ʘ

19.  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)

20.  E k : SN kinetic energy = 0.1*E exp E bin : Binding energy of a proto-glaxy ε (=0.1): minimum outflow energy rate M sw : 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

21.  IMF:  Lognrmal IMF, M md =200M ʘ (Pop. III.1), M md =40M ʘ (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. t merge Main halo Mass: M mh (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 t merge = radius of a spherical shell with M which collapse at t merge We computed distance and radial velocity of mini-halos as a function of t merge and M mh (t merge ). Where t merge is a age when the mini-halo accrete to the main halo and M mh (t merge ) is the mass of main halo at the merger. d 2 r/dt 2 = -GM/r 2 + Λ c 2 r/3

23. time Universe d 2 r/dt 2 = -GM/r 2 + Λ c 2 r/3

24. Main halo r init Angle Θ (random) Mini halo v init d 2 r/dt 2 = -G(M main (t)+4π ρ av r(t) 3 /3)/r 2 + Λ c 2 r/3 + l 2 /r 3 l = r(t form )v esc sin θ

26.  In the Milky Way halo Hyper metal poor stars = Pop. III survivors ? object [Fe/H] [C/Fe] HE0107-5240: -5.4 +3.7 HE1327-2326: -5.7 +4.16 HE0557-4840: -4.8 +1.65 SDSSJ102915+172927 : -4.7 <0.93 Fe: accretion of ISM C, N. Mg.. : binary mass transfer

27.  PISN ? (~200 M ʘ )  Low [Zn/Fe]  High [Si/Fe], [Ca/Fe]  Odd even effect  Type II ? (10 – 50 M ʘ )  (typical abundance of the halo stars)  Hypernovae ? ( 20 – 50 M ʘ )  Large [Zn/Fe]  (Fast rotating star ?)  (Supermassive star ?) Umeda & Nomoto (2002)

28.  Mass ratio  Sana & Evans 2010

29. Raghavan et al. 2010

31.  In the Milky Way halo  Formation epoch

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

33. Metal enrichment history of the CGM