Evolution of Newly Formed Dust inPopulation III Supernova Remnants andIts Impact on the Elemental Compositionof Population II.5 Stars
Takaya Nozawa（Hokkaido University）
T. Kozasa, A. Habe (Hokkaido University),
E. Dwek (NASA Goddard Space Flight Center),
H. Umeda (Univ. of Tokyo), N. Tominaga (NAOJ)
K. Maeda (IPMU), K. Nomoto (Univ. of Tokyo, IPMU)

1. Introduction (1)○ Role of dust in the early universe
・ Dust absorb stellar light and re-emit it by thermal radiation,➔ plays a crucial role in interpreting the SFR and the IMFof the early generation of stars from high-z observations
・ Dust provides additional pathways for cooling of gas throughtheir thermal emission and H2 formation on their surfaces➔ has great impacts on the formation processes of stars
The absorption and thermal radiation by dust grains strongly
depend on their chemical composition, size, and amount

It is essential to clarify the properties ofdust in the early epoch of the universe!

1. Introduction (2)○ Sources of dust in the early universe
・ At z > 5, the main formation sites of dust are considered
to be in the ejecta of supernovae (SNe)・ The newly condensed dust is processed via sputtering in
the hot gas swept up by the reverse and forward shocks
The efficiency of dust destruction is sensitive to the chemicalcomposition and size
We investigated the formation of dust in Population III SNe(Nozawa et al. 2003)➔ the chemical composition, size distribution, and massof dust grains formed in the SN ejecta

2. Aim of our study
We investigate the evolution of dust grains formedin Population III SNe・ the processing of dust through the collisions withthe reverse shocks penetrating into the ejecta
・ the transport of dust within SN remnants (SNRs)
chemical composition, size distribution, and amountof dust finally injected from SNe into the ISM

influences of dust on the elemental composition ofPopulation II.5 stars(the second-generation stars formed in the dense shell of Pop III SNRs;
Mackey et al. 2003; Salvattera et al. 2004; Machida et al. 2005)

3. Dust evolution in SNRs
Reverse shock 接触不連続面
Forward shockcontact↓↓↓
discontinuity

Dust
ダスト→→

hot
高温

高温

direction of ←shock→：shock の向き→：ガスの速度→→←ejecta→｜ ISMhot→

velocity of gas

・ kinetic sputtering : due to relative velocity of dust to gas
・ thermal sputtering ： due to thermal velocity of gas
The deceleration rate and erosion rate of dust
⇐ the temperature and density of gas⇐ the relative velocity of dust to gas

3. Dust evolution in SNRs
Reverse shock 接触不連続面contact
↓
↓

Dust
ダスト

Forward shock↓

discontinuity

→

→

→

→
高温
hotdirection←→：shockの向きof shock高温
hot←ejecta→｜ ISM→

velocity of gas→：ガスの速度・ kinetic sputtering : due to relative velocity of dust to gas
・ thermal sputtering ： due to thermal velocity of gas
The deceleration rate and erosion rate of dust
⇐ the temperature and density of gas⇐ the relative velocity of dust to gas

3-1. Time evolution of SNRs

3-2. Physics of dust in SNRs

3-3. Initial conditions○ Models of Pop III SNe (Umeda & Nomoto 2002)
・ Type II SNe (SNe II) : Mpr=13, 20, 25, 30 M☉ (E51=1)○ The ambient medium (homogeneous)・ gas temperature ; T = 104 K・ gas density ; nH,0 = 0.1, 1, 10 cm-3

○ Dust in the He core (Nozawa et al. 2003)
・ size distribution and spatial distribution of each grain
species formed in the unmixed ejecta
・ dust grains → test particles
The calculation is performed from 10 yr up to ~106 yr.

4-1. Temperature and density of gas
Model : Mpr=20 M☉ (E51=1)
nH,0 = 1 cm-3
Downward-pointing arrows:
forward shock in upper panel
reverse shock in lower panel
The temperature of the gas
swept up by the shocks➔ 106-108 K↓Dust grains residing in this hotgas are eroded by sputtering4-2. Evolution of dust in SNRs
Dust grains in the He core
collide with reverse shock at(3-13)✕103 yr
The evolution of dust heavily
depends on the initial radiusand compositionaini = 0.01 μm (dotted lines)➔ completely destroyedaini = 0.1 μm (solid lines)➔ trapped in the shellaini = 1 μm (dashed lines)➔ injected into the ISM

4-3. Size distribution of surviving dust

The size distribution of surviving dust is greatly deficient insmall-sized grains, compared with that at its formation
The grains in the early ISM are relatively large (> 0.01 μm)This result is almost independent on the progenitor mass

4-4. Total mass of surviving dust
The initial radius below which
dust is completely destroyedaini ＜～0.01 μm
for nH,0 = 0.1 cm-3
aini ＜～0.05 μm
for nH,0 = 1 cm-3
aini ＜～0.2 μm
for nH,0 = 10 cm-3
The total mass of surviving dust decreases with increasing
the density in the ambient medium

total mass of surviving dust； 0.01-0.8 M☉ for nH,0 = 10-0.1cm-3(total mass of dust at the formation； 0.2-1 M☉)

5-1. Elemental abundance in the shell (1)dust grains surviving the destruction but not injected into theambient medium are piled up in the dense shell in 10 5 to 106 yr↓
・ dust in the shell may enable to the formation of stars with solar
mass scales through its thermal emission for matellicities of-6< log(Z/Z☉) <-4 (Omukai et al. 2005; Schneider et al. 2006)
・ It is expected that the elemental composition of piled-up grains
reflects the elemental abundance of Population II.5 stars
formed in the shell of SNRs↓
We calculate the metal abundance patterns in the shell,and compare with observations of HMP and UMP stars

5-2. Elemental abundance in the shell (1)5-3. Elemental abundance in the shell (3)－6 ＜ [Fe/H] ＜－5

0 ＜ [Mg, Si/Fe] ＜ 2↓
Elemental composition ofdust piled up in the shell
can reproduce abundance
patterns in HMP stars
The transport of dust
segregated from metal-richgas can be responsible forthe abundance patterns in
HMP and UMP stars

5-4. Elemental abundance in the shell (4)We assume that the gas
outside the innermost Felayer in the ejecta isincorporated into the shell↓
reproducing the extremeoverabundance of C and O
leading to more than 100
time excesses of Mg and Si
It might be possible toreproduce the elemental
abundances of HMP stars if
the SI-Mg-rich layer is not
mixed the gas in the shell6. Summary
1. Once dust grains inside the He core collide with the reverse
shock, they undergo the different transport and destruction inSNRs, depending on their initial radii and compositions.
2. Size distribution of surviving dust is largely deficient in smallsized grains, compared with that at the time of dust formation.

3. Total mass of surviving dust is 0.01-0.8 M☉ and decreases
with increasing the ambient gas density.
4. Segregation of dust from metal-rich gas can be responsible forabundances of Mg, Si, and Fe in HMP stars if they were thesecond-generation stars formed in the shell of Pop III SNRs.
5. It might be possible to reproduce the elemental abundance ofHMP stars if SI-Mg-rich layer is not mixed the gas in the shell.