yutaka komiya (national astronomical observatory of japan) takuma suda (naoj), masayuki y. fujimoto...
TRANSCRIPT
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Yutaka Komiya (National Astronomical Observatory
of Japan)Takuma Suda (NAOJ),
Masayuki Y. Fujimoto (Hokkai Gakuen Univ.)
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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 ?
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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)
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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
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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
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22
2
22
2s
s
cvcv
Gmm
EMP star
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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
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~ 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
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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
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~ 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
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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
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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
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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
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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
(?)
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IMF of Pop.III Mmd=10Mʘ
Minimum halo mass Tvir > 104 K
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MDF
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Chemical signature
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Parameter dependenceMmd(Pop.III.1) = 40Mʘ
Mmd(Pop.III.1) = 10Mʘ
Zcr = 10-4Zʘ
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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)
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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
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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
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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
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time
Universe
d2r/dt2 = -GM/r2 + Λc2r/3
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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
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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
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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)
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Mass ratio Sana & Evans 2010
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Raghavan et al. 2010
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In the Milky Way halo Formation epoch
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Formation redshift of low mass EMP stars (red) and Pop.III stars (green) .
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Metal enrichment history of the CGM