2016/02/12

超新星ダストのサイズ分布
野沢 貴也（Takaya Nozawa）
国立天文台 理論研究部(National Astronomical Observatory of Japan)

Contents:- Introduction- Dust formation in supernovae (SNe)- Dust destruction by SN reverse shocks- Observations of dust size (distribution) in SNe

1-1. Introduction〇 Supernovae (SNe) are major sources of dust?
- abundant metal (metal : N > 5)
- low temperature (T < ~2000 K)- high density (ni > ~106 cm-3)- mass-loss windsof AGB stars- expanding ejectaof SNe‐ contribution of dust mass from AGB stars and SNe
N(AGB stars) / N(SNe) ~ 10-20 (Salpeter IMF)
Mdust = 0.01-0.05 Msun per AGB star (e.g., Zhukovska & Gail 2008)
Mdust = 0.1-1.0 Msun per SN (e.g., Nozawa+2003, 2007)‐ huge amounts of dust grains (>108 Msun) at redshift z > 5➔ 0.1 Msun of dust per SN is needed to be ejected (Dwek+2007)

what composition, size, and mass of dust are ejected by SNe?

1-2. Summary of observed dust mass in CCSNe

missing cold dust?

young SNRs

Type II-P SNe

swept-up IS dust?

There are increasing pieces of evidence that massive
dust in excess of 0.1 Msun is formed in the ejecta of SNe

1-2. Summary of observed dust mass in CCSNe

missing cold dust?

young SNRs

Matsuura+2011

Type II-P SNeBalow+2010

Gomez+2012

swept-up IS dust?

There are increasing pieces of evidence that massive
dust in excess of 0.1 Msun is formed in the ejecta of SNe

1-3. Formation and processing of dust in SNe
Nozawa 2014, Astronomical Herald

Destruction efficiency of dust grains by sputtering in thereverse shocks depends on their initial size
The size of newly formed dust is determined by physicalcondition (gas density and temperature) of SN ejecta

1-4. Achievement and issues on SN dust
〇 これまでの研究でわかったこと（重力崩壊型）超新星は、放出ガス中で大量（0.1 Msun以上）のダストを形成することができる〇 超新星ダスト研究における現在の二つの課題
1) 観測された大量のダストはいつ形成されたのか？
➜ 中間赤外線と遠赤外線でのダスト量の違いを説明したい

2) 形成されるダストのサイズはどれくらいか？
➜ 超新星による最終的なダスト放出量を明らかにしたい2. Size and mass of dust formedin core-collapse supernovae

2-1. Dust formation in primordial SNe
Nozawa+2003, ApJ, 598, 785〇 SN model (Population III SNe) (Umeda & Nomoto 2002)‐SNe II ： MZAMS = 13, 20, 25, 30 Msun (E51=1)
after 600 days

‐layered elemental distribution in the metal-rich He core‐no mixing of elements within the He-core‐gas density: ρ ~ 10-14-10-13 g/cm3 ➜ n ~ 108-1010 /cm3

2-2-1. Grain species considered in this study〇 dust formation theory‐nucleation‐grain growth
taking account of chemical
reaction at condensation(Kozasa & Hasegawa’87)# key species：
gas species with theleast collision frequency
among reactants
key species controls thekinetics of the nucleationand grain growth2-2-2. Nucleation rate
Steady-state nucleation rate

Supersaturation ratio

2-2-3. Basic equations for dust formation
・ Equation of mass conservation

・ Equation of grain growth

Growth rate is independent of grain radius

2-3. Dust formed in Type II-P SNeaverage radius

0.01 μm

condensation time‐a variety of grain species cancondense according to elemental
composition in each layer‐ condensation time:
300-600d after explosion‐ average grain radii: >~0.01 μm
Nozawa+03, ApJ, 598, 785

2-5. Size distribution of newly formed dustNozawa+2003, ApJ, 598, 785‐C, SiO2, and Fe grains have lognormal-like size distribution,
while the other grains have power-law size distribution‐Size distribution summed up over all grain species is roughly
described by a broken power-law with the index of -2.5 and -3.5
‐Size distribution of dust in mass has a peak around 0.1-1 µm

2-4. Behavior of dust formation

2-5. Size distribution of newly formed dust
Nozawa+2003, ApJ, 598, 785‐C, SiO2, and Fe grains have lognormal-like size distribution,
while the other grains have power-law size distribution‐Size distribution summed up over all grain species is roughly
described by a broken power-law with the index of -2.5 and -3.5

‐Size distribution of dust in mass has a peak around 0.1-1 µm

2-6. Scaling relation of average grain radius
Nozawa & Kozasa (2013)

CMgSiO3

Λon > 30

Λon > 30

Λon = τsat/τcoll : ratio of supersaturation timescale to gas
collision timescale at the onset time (ton) of dust formation

Λon = τsat/τcoll ∝ τcool ngas
・ fcon,∞ and aave,∞ are uniquely determined by Λon・ steady-state nucleation rate is applicable for Λon > 30

3. Destruction of dust grains by
SN reverse shocks
T = (1-2)x104 K
nH,0 = 0.1-1 cm-3

He coreFSRSCD

3-1. Time evolution of SNRs

3-2. Dynamics of dust

3-3. Erosion rate of dust by sputtering3-4. Erosion rate of dust by sputtering
Nozawa+2006, ApJ, 648, 435

projectile: H and He

projectile: oxygen ions・ erosion rate by sputtering quickly increases above
105 K and peaks at 107 -108 K・ erosion rate : da / dt ~ 10-6 nH μm yr-1 cm3for the primordial gas (H and He) at T > 106 K

3-5. Temperature and density of gas in SNRs
Nozawa+07, ApJ, 666, 955

Model : M pr= 20 Msun (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 theshocked hot gas are erodedby sputtering3-6. Evolution of dust in SNRs
モデル : Mpr= 20 Msun (E51=1), nH,0 = 1 cm-3
ダストの軌道○ 超新星残骸内でのダストの進化は、ダストの初期半径と組成に強く依存する
aini = 0.01 μm (dotted lines)➔ 完全に破壊される
ダスト半径の時間進化

aini = 0.1 μm (solid lines)➔ shell中に捕獲される
aini = 1 μm (dashed lines)➔ 星間空間に放出される

3-7. Dust mass and size ejected from SNe II
Nozawa+07, ApJ, 666, 955

SNe II

total mass of dust surviving thedestruction in Type II SNRs;
0.07-0.8 Msun (nH,0 = 0.1-1 cm-3)
size distribution of dust after theshock-destruction is domimatedby large grains (> 0.1 μm)

3-8. Comparison with other studies

Schneider+2011- dust formation in the one-zone ejecta of SNe➜ log-normal size distribution at dust formation- reverse shock destruction increases small grains➜ larger grains must be dominant in mass

Nozawa+2007

4. Observations of size distributionof dust in SNe4-1. Composition of dust formed in SNeinterstellar dust : carbonaceous grainsilicate (MgFeSiO4?)

silicate
Matuura+2011, SN 1987A

carbonKotak+09, 2004et

Douvion+01, Cassiopeia A SNR

4-2. Properties of dust in SN 1987A
SN 1987A
HαWesson+2015

OI 6300- Md ~ 0.7 Msun
- a ~ 0.2 µm
large radius is required tohave Tdust ~ 20 K in LMC
At 714 dayBevan & Barlow 2016

・ dust mass < 7x10-2 Msun・ grain radius > ~0.6 µm

4-3. Dust formation in Type IIn SN 2010jl

carbonT = 1300 K

silicate
T = 1450 K

4-4. Dust properties in Type IIn SN 2010jl
opticallight curve

Dust in SN 2010jl
・ carbon grains

・ dust mass: ~10-3 Msun・ grain radius: <0.1μm(possibly <0.01 µm)
Maeda, TN, et al. (2013)

4-5. Dust formation in Type IIn SN 2010jl

Power-law sizedistribution
・ α : ~3.5・ maximum radius :~3-4 µm (>0.5 μm)

Gall+2014, Nature4-6. Dust properties in one knot of Cas A SNR

Douvion+01, Cassiopeia A SNR

Cool dust component

Far-side is more obscured
han near-side
E(B-V) = 0.23

・ Fe with < ~0.01 Msun(or large Si dust)
Lee, Koo et al. 2015, ApJ, 808, 98

4-7. Formation condition of presolar Al2O3
Nozawa+2015, ApJ, 811, L39
presolar Al2O3 grains

Choi+1998

Submicron-sized presolar Al2O3 grains identified as
SN-origin were formed in dense clumps in the ejecta

5. Summary(1) 超新星でのダスト形成
様々なサイズ（数Å～１µm）のダストが形成される➜ 0.1-1 µmあたりにピークを持ちそう （ガス密度に依存）(2) リヴァース衝撃波によるダスト破壊
小さいサイズ（~0.01 µm以下）のダストは破壊される➜ 大きいダスト（~0.1 µm以上）が支配的に放出される(3) 超新星ダストのサイズ（分布）の観測
SN 1987Aでは、0.1 µmより大きいであろう
Cassiopeia Aのダストは小さめかもプレソーラーグレインは、かなり大きい（>1 µm）ものもある➜ 超新星放出ガスがクランプ状になっている必要がある