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) • Asano, Takeuchi, Hirashita, Nozawa (2013, MNRAS, 432, 637) • Asano, Takeuchi, Hirashita, Nozawa (2014, MNRAS, 440, 134) • Nozawa, Asano, Hirashita, Takeuchi (2015, MNRAS, 447, L15)
O Discovery of massive dust in excess of 108 Msun in quasar hosts at z > 5 (Bertoldi+2003, Priddey+2003, Robson+2004, Beelen+2006) -  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 - 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)
A / A
(Draine 2009; Michalowski+2010; Gall+2011a, 11b; Pipino+2011; Mattsson+2011; Valiante+2011; Inoue 2011; Kuo & Hirshita 2012; Calura+2014; Michalowski 2015)
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
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
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 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
grain radius (μm) grain growth: accretion of gas-phase heavy elements onto pre-existing dust coagulation
- one-zone closed-box model (no inflow and no outflow) - SFR(t) = Mgas(t)/TSF (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
- evolution of dust mass ΔMd(a,t) with radii between a and a+da xSFR(t), astration
dt ∆ Ma (a,t) dust production by SNe II and AGB stars M ISM ( t ) Mswept mm(a) )SN(t) Mism (t)
shock destruction + TICNM coag,CNM coagulation r 100 M O AYa(a,t) Δmd(m, Z(t — τm), a)φ(m)SFR(t Meut (t)
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 - 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
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
- two-phase ISM • WNM (T = 6000 K, n = 0.3 cm -3) • 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 0 N 6 8 4 10 1/λ [μm-1] 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
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 - TSF = 0.5 Gyr Grain growth is necessary to achieve the observed high D/G Galactic age [Gyr] Nozawa+2015
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 high- z 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)
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