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2015/04/15
高赤方偏移クェーサー母銀河中の
星間ダスト進化と減光曲線
(Evolution of grain size distribution in high-redshift dusty quasars:
integrating large amounts of dust and unusual extinction curves)
野沢 貴也 （Takaya Nozawa）
国立天文台 （NAOJ） 理論研究部
共同研究者
浅野 良輔、竹内 努 (名古屋大学)、平下 博之 (ASIAA)
References
・ Asano, Takeuchi, Hirashita, Nozawa (2013, MNRAS, 432, 637)
・ Asano, Takeuchi, Hirashita, Nozawa (2014, MNRAS, 440, 134)
・ Nozawa, Asano, Hirashita, Takeuchi (2015, MNRAS, 447, L15)
1-1. A large amount of dust in high-z quasars
○ Discovery of massive dust in excess of
108 Msun in quasar hosts at z > 5
(Bertoldi+2003, Priddey+2003, Robson+2004, Beelen+2006)
e.g., SDSS J1148+5251 at z=6.4
-
cosmic age : 890 Myr
stellar mass : ~1011 Msun
SFR : ~3000 Msun/yr (Salpeter IMF)
gas mass : >~3x1010 Msun
IR luminosity : (1-3)x1013 Lsun
dust mass : (2-7)x108 Msun
dust-to-gas mass ratio : ~0.01
Bertoldi+2003
stellar
emission
dust
emission
○ Sources of dust in the early universe
➜ core-collapse supernovae (CCSNe)
‐dust evolution model : >0.1-1 Msun per SN
(Morgan & Edmunds 2003; Maiolino+2006; Dwek+2007)
Leipski+2010
‐theoretical studies of dust formation : ~0.1-1.0 Msun per SN
(Todini & Ferrara 2001; Nozawa+2003, 2007; Bianchi & Schneider 2007)
1-2. Extinction curves in high-z quasars
SDSS J1048+4637 at z=6.2 :
broad absorption line (BAL) quasars
UV extinction curve
Maiolino+2004, Nature, 431, 533
The interstellar dust in the epoch
as early as z=5 was predominantly
supplied by CCSNe?
1-3. What are dust sources in quasars at z > 5?
Gas mass (Msun)
○ AGB stars + SNe
Gas mass (Msun)
Calura+2014
Dwek & Cherchneff (2011)
‐AGB stars contribute more dust grains than
CCSNe (Valiante+2009; Dwek & Cherchneff 2011)
‐dust formation calculation: 0.01-0.05 Msun
per AGB star (Zhukovska & Gail 2008)
○ Grain growth in molecular clouds + AGB stars + SNe
(Draine 2009; Michalowski+2010; Gall+2011a, 11b; Pipino+2011; Mattsson+2011;
Valiante+2011; Inoue 2011; Kuo & Hirshita 2012; Calura+2014; Michalowski 2015)
1-4. Inconsistency in the origin of high-z dust
unusual extinction curve
huge amounts of dust grains
Can we explain self-consistently the massive dust and
unusual extinction curve observed for high-z quasars?
SN dust only !
???
SN dust
+
AGB dust and dust growth
1-5. Life-cycle of interstellar dust
ビッグバン
分子雲中での
ダストの成長
星間空間中での
ダストの破壊・変性
星間空間
原始惑星系円盤
惑星系の形成
分子雲
星の誕生
大質量星
中小質量星
超新星爆発
星間空間への
ダスト供給
質量放出
ダストは様々な天体現象と密接に関わっており、銀河中のダストの
サイズ分布・存在量は星形成活動とともに時々刻々と変化する
1-6. Aim of our study
In the past dust evolution models, the size
distribution of dust is assumed to be
- a single size (e.g., a=0.01 µm or 0.1 µm)
or
- that in our Galaxy, with no time evolution
Gall+2011a
Recently, we constructed, for the first time, the evolution model of
dust size distribution, which considers the following dust processes:
- production of dust in CCSNe and AGB stars
- destruction of dust by interstellar shocks
- grain growth due to metal accretion in molecular clouds
- shattering and coagulation due to grain-grain collisions
(Asano, Takeuchi, Hirashita, TN 2013)
We apply this dust evolution model to study the evolution of dust
size distribution and the extinction curves in high-z dusty quasars
2-1. Formation/destruction processes of dust
Dust ejected from CCSNe
Dust ejected from AGB stars
coagulation
Nozawa+2007
grain growth:
accretion of gas-phase heavy
elements onto pre-existing dust
Yasuda & Kozasa 2012
shattering
Sirono+2013
Hirashita & Yan+2009
2-2. Dust evolution model in a galaxy (1)
‐one-zone closed-box model (no inflow and no outflow)
‐SFR(t) = Mgas(t)/τSF (Schmidt law with n = 1)
‐Salpeter IMF: φ(m) = m-q with q=2.35 for Mstar = 0.1-100 Msun
‐dust processes
-
production of dust in SNe II and AGB stars
destruction of dust by interstellar shocks
grain growth due to metal accretion in molecular clouds
shattering and coagulation due to grain-grain collisions
‐two dust species:
- graphite (carbonaceous grains)
- silicate (grains species other than carbonaceous grains)
‐multi-phase ISM
- WNM (warm neutral medium): T = 6000 K, n = 0.3 cm-3
- CNM (cold neutral medium): T = 100 K, n = 30 cm-3
2-3. Dust evolution model in a galaxy (2)
‐evolution of dust mass ΔMd(a,t) with radii between a and a+da
xSFR(t), astration
dust production by SNe II and AGB stars
shock destruction
grain growth
shattering
coagulation
2-4. Evolution of extinction curves in galaxies
grain size distribution
dust amount
extinction curve
MRN
τSF=5 Gyr
WNM=0.5
CNM=0.5
Asano, Takeuchi, Hirashita, TN+2013, 2014
‐early phase : formation of dust in SNe II and AGB stars
➔ large grains (>0.1 μm） are dominant ➔ flat extinction curve
Asano+12
‐middle phase : shattering, grain growth due to accretion of gas metal
➔ small grains (< 0.03 μm） are produced ➔ steep extinction curve
‐late phase : coagulation of small grains
➔ shift of peak of size distribution ➔ making extinction curve flatter
2-5. Life-cycle of interstellar dust
ビッグバン
分子雲中での
ダストの成長
星間空間中での
ダストの破壊・変性
星間空間
小さいダスト
の支配的成長
原始惑星系円盤
惑星系の形成
乱流中の衝突破砕に
よる小さいダストの生成
分子雲
星の誕生
大質量星
中小質量星
超新星爆発
星間空間への
ダスト供給
比較的大きいダストの供給
質量放出
ダストは様々な天体現象と密接に関わっており、銀河中のダストの
サイズ分布・存在量は星形成活動とともに時々刻々と変化する
3-1. Reproducing the MW extinction curve
‐two-phase ISM
・ WNM (T = 6000 K, n = 0.3 cm-3)
WNM=0.5
CNM=0.3
MC=0.2
・ CNM (T = 100 K, n = 30 cm-3)
‐three-phase ISM
・ WNM (T = 6000 K, n = 0.3 cm-3)
・ CNM (T = 100 K, n = 30 cm-3)
・ MC (molecular clouds)
➜ T = 25 K, n = 300 cm-3
Nozawa+2015
- three-phase ISM model including the MC phase can reproduce
the average extinction curve in the MW
- ISM phase is one of the important quantities in constructing the
evolution model of interstellar dust
3-2. Explaining massive dust in high-z quasars
high-z quasar host: starburst galaxies
➜ indicating a high fraction of MC
MH2/MH,total ~ 0.7-0.97 (Calura+2014)
‐two-phase ISM:
WNM=0.3 and MC=0.7
‐τSF = 0.5 Gyr
Grain growth is necessary to
achieve the observed high D/G
Nozawa+2015
3-3. Explaining the high-z extinction curves
The presence/absence of 2175 A
bump may be related to the dust
composition of dust rather than
the dust evolution model
- graphite and silicate
- amorphous carbon & silicate
➜ the derived extinction curve
well match the observed highz extinction curve
Nozawa+2015
The origin of the 2175 A bump is still unclear
➜ small size (<0.02 µm) of graphite? (e.g., Draine & Lee 1984)
➜ PAHs (polycyclic aromatic hydrocarbon?) (e.g., Joblin+1992)
・ formation site of PAHs
- AGB stars? (bottom-up scenario) (e.g., Cherchneff+1993)
- shattering of C grains? (up-down scenario) (e.g., Seok+2014)
4. Summary
We investigate the evolutions of grain size distribution
and the extinction curves in high-z dusty galaxies
・ our dust evolution model can reproduce the average
extinction curve in the MW by considering
- three-phase ISM (WNM=0.5, CNM ~ MC ~ 0.25)
- graphite & silicate
・ a large amount of dust grains and the unusual extinction curve
observed for high-z quasars can be explained by considering
- a large mass fraction of MC (>0.5) in the ISM
➜ efficient growth/coagulation of dust grains
- amorphous carbon & silicate
➜ different properties of carbonaceous dust
## It is possible that the quasar extinction curves reflect the properties
## of dust in circumnuclear (AGN) torus, not those of interstellar dust