2015/05/25

Dust Production Factories
in the Early Universe
Takaya Nozawa（National Astronomical Observatory of Japan）- Formation of dust in very massive Pop III RSGs
Nozawa, T., Yoon, S.-C., Maeda, K., Kozasa, T., et al.,(2014), ApJ, 787, L17- Evolution of dust in high-redshift dusty quasars
Nozawa, T., Asano, R. S., Hirashita, H., Takeuchi, T. T.
(2015), 447, L16

1-1. Sources of dust in the early unvierse
・ Origin of massive dust at high redshifts (z > 5)
- core-collapse supernovae (CCSNe) may be promising sourcesof dust grains (e.g., Todini & Ferrara 2001; TN+2003; Dwek+2007)- the contribution from AGB stars is also invoked to explain theobserved dust mass (e.g., Valiante+2009; Dwek & Cherchneff 2011)➔ what stellar mass range can mainly contribute dust budget
in the early universe depends on the initial mass function
Hirano+2014

・ Typical mass of Pop III stars➔ Pop III stars may be much more
massive than Pop I/II stars- ~40 Msun (Hosokawa+2011; Susa 2013)- >300 Msun (Omukai+2003; Ohkubo+2009)- 10-1000 Msun (Hirano+2014, Susa+2014)

1-2. Very massive Population III stars
・ Role of very massive stars (MZAMS > ~250 Msun)- emitting numerous ionizing photons➔ reionization of the universe- finally collapsing into black holes➔ serving as seeds of SMBHs

・ Evolution of massive Pop III stars- non-rotating stars with MZAMS > 250Msun
undergo convective dredge-up of C andO during the RSG phase (Yoon+2012)

Yoon+2012- enriching the surrounding medium
with CNO through the RSG winds➔ serving as formation sites of dust
m500vk00

Dust grains formed in the winds are not
likely to be destroyed by the SN shocks

1-3. Model of Pop III red-supergiant winds
・ Formula of non-steady-state dust formation(Nozawa & Kozasa 2013)

・ RSG model: m500vk00 (Yoon+2012)- MZAMS = 500 Msun (no rotation)- L = 107.2 Lsun, Tstar = 4440 K, Rstar = 6750 Rsun
- AC = 3.11x10-3, AO = 1.75x10-3 ➔ C/O = 1.78, Z = 0.034

・ Model of circumstellar envelope- spherically symmetry, constant wind velocity- density profile:- temperature profile:- wind velocity: vw = 20 km/s
- mass-loss rate: Mdot = 0.003 Msun/yr➔ losing 90% (208 Msun) of envelope during 7x104 yr of the RSG

1-4. Dependence on Mdot and vw- gas density: ngas ∝ 1/vw
∝ vw-1.75∝ Mdot0.88- cooling time:Τcool = [ (1/T)(dT/dt) ]-1 ∝ 1/vw

Nozawa+2014- The condensation efficiency of dust is unity for the condition;- for the fiducial case (Mdot = 3x10-3 Msun/yr, vw=20 km/s, fc=1)
 1.7 Msun of C grains is produced over the lifetime of the RSG

1-5. How efficient is dust formation?
・ Dust ejection efficiency by very massive Pop III RSGs
- XVMS = Mdust / MZAMS < 3.4x10-3 = ~0.3 %- Mdust / Mmetal < 0.24

・ Dust ejection efficiency by CCSNe- XCCSN = (0.1-30)x10-3 = 0.1-3.0 %- Mdust / Mmetal = 0.01-0.25 (Mdust / Mmetal < 0.15)

Hirano+2014## The ranges above reflects the destruction## efficiency of dust by the reverse shock
CCSNe

If NVMS ~ NCCSN in the Pop III IMF …
➔ The contribution of dust from verymassive RSGs is comparable with,or even higher than that from CCSNe(XVMS NVMS) / (XCCSN NCCSN) ~ 1VMSs

1-6. Summary and discussion
We examine the possibility of dust formation in a massloss wind of a Pop III RSG with MZAMS = 500 Msun
- The condensation efficiency is unity for➔ the first dust grains in the universe ??
- The mass of C grains is <1.7 Msun （Mdust/MZAMS < 3.4x10-3), which
would be high enough to have impacts on dust enrichment history
in the early universe, if the IMF of Pop III stars were top-heavy- Very massive Pop III stars might supply dust grains only at thevery early phase of the universe- Our study proposes a new scenario of dust formation in Pop IIIstars as possible sources of dust in the early universe

2-1. What are dust sources in quasars at z > 5?

Gas mass (Msun)

Gas mass (Msun)

What is the sources of massive dust grains?
○ only SNe

Calura+2014

SDSS J1148+5251
at z=6.4‐ 0.1-1.0 Msun per SN (e.g., Nozawa+2003, 2007)○ AGB stars + SNe‐ 0.01-0.05 Msun per AGB star (Zhukovska & Gail 2008)

Beelen+2006○ 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)

2-2. 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?

2-3. Inconsistency in the origin of high-z dust
unusual extinction curve

huge amounts of dust grains

Can we explain self-consistently the massive dust andunusual extinction curve observed for high-z quasars?

SN dust only !

???

SN dust+AGB dust and dust growth2-4. Dust evolution model in a galaxy
Asano, Takeuchi, Hirashita, TN (2014a, 2014b)‐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 and silicate‐multi-phase ISM- WNM (warm neutral medium)- CNM (cold neutral medium)- MC (molecular cloud)

WNM=0.5
CNM=0.3
MC=0.2

Our Galaxy

2-5. 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)

Growth of small grains via
accretion of gas in the MCs‐two-phase ISM:
WNM=0.3 and MC=0.7‐τSF = 0.5 Gyr
Grain growth is necessary toachieve the observed high D/GEjection of large grainsfrom SNe and AGB stars

Nozawa+2015

Production of small grains
via shattering in the ISM

2-6. Explaining the high-z extinction curves

Nozawa+2015

The presence/absence of 2175 A
bump may be related to the dust
composition of dust
- graphite and silicate- amorphous carbon & silicate➜ the derived extinction curve
well match the observed highz extinction curve2-7. SummaryWe investigate the evolutions of grain size distribution
and the extinction curves in high-z dusty galaxies
・ 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 (instead of graphite & silicate)➜ different properties of carbonaceous dust