2014/05/21

Evolution of dust size distribution andextinction curves in galaxies
Takaya Nozawa(National Astronomical Observatory of Japan)
Collaborators:
Asano, S. Ryosuke (Nagoya University)
Takeuchi, T. Tsutomu (Nagoya University)
Hirashita, Hiroyuki (ASIAA)
References
・ Asano, Takeuchi, Hirashita, Nozawa (2013, MNRAS, 432, 637)
・ Asano Takeuchi, Hirashita, Nozawa (2014, MNRAS, 440, 134)
・ Asano, Nozawa, Hirashita, Takeuchi (2014 in prep.)1-1. Dust alters the SEDs of galaxies
M82

Silva+1998

Dust absorbs UV/optical lights
and re-emits thermal emission
in the infrared
70% of the star formation activity
at 0.5 <z< 1.2 is obscured by dust
Takeuchi+2005

1-2. Aim of our study
to correct the obscuration by dust, many (observational) studies
have assumed the MW, SMC, LMC extinction curves or the Calzettiextinction (attenuation) law➔ however, the size distribution of interstellar dust must change
as the galaxy evolves

we construct the evolution model of grain size distribution, withthe aim at understanding how the extinction curve is modified in
the course of galaxy evolution・ dust processes considered in our works- 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

2-1. Extinction curves in the Milky Way〇 MRN dust model(Mathis, Rumpl, & Nordsieck 1977)## total-to-selective extinction ratio##
RV = AV / (AB – AV)

・ composition :silicate and graphite

・ small grains (small Rv)➜ steep extinction curve

・ size distribution :n(a) ∝ a^{-q} with q=3.5,0.005 μm ≤ a ≤ 0.25 μm

・ large grains (large Rv)➜ flat extinction curve2-2. Properties of dust ejected from SN II-P
Nozawa+07, ApJ, 666, 955

SNe II

mass of dust grains injected froma SN II into the ISM:
0.07-0.8 Msun (nH,0 = 0.1-1 cm-3)

size distribution of dust which isejected from SNe II is domimatedby large grains (> 0.01 μm)

at time of dust formation

after destruction of dust
by reverse shock2-3. Properties of dust ejected from AGB stars
solid: carbon
dashed: silicate
dotted: the others

Zhukovska & Gail 2008; Valiante+2009
SiC grainmass of dust grains injected froma AGB star into the ISM:
0.001-0.01 Msun (Mstar > 1 Msun)
average radius of dust ejectedfrom AGB stars is considered tobe large (a = 0.1-1.0 μm)
Yasuda & Kozasa 2012

2-4. Destruction of dust in SN shocks
sputtering

projectiles: H and He

sputtering: ejection of atoms
from dust surface

・ erosion rate by sputtering: da/dt ~ 10-6 (nH / 1.0 cm-3) μm yr-1
(e.g., Nozawa+2006, ApJ, 648, 435)

・ timescale of dust destruction by SN shocks, τdest
τdest = [ (1/Mdust)(dMdust/dt) ]-1 = [ ε Mswept RSN / Mgas ]-1~ 5x108 yr (ε / 0.3)-1 (Mswept / 3000 Msun)-1 (RSN / 0.02 yr-1)-1x (Mgas / 1010 Msun)

2-5. Growth of dust in molecular clouds
grain growth

grain growth:
accretion of gas-phase heavy
elements onto pre-existing dust

Sirono+2013

・ timescale of grain growth, τgrow
τgrow = [ (1/md)(dmd/dt) ]-1 = [ (1/3a) αs nmetal V0 <v> ]-1~ 2x107 yr (αs / 0.2)-1 (a / 0.01 μm) (Z / 0.02)-1 (ngas / 30 cm-3)-1➔ grain growth is more efficient for a higher gas density, a higher
metallicity (higher abundance of metals), and a smaller grain## grain growth is more efficient for a large surface-to-volume
ratio of dust grains

2-6. Shattering and coagulation of dust
shattering・ shattering at vrel > vshat
where vshat = 1-3 km/s
・ coagulation at vrel < vcoag
where vcoag = 0.01-0.1 km/s
in the interstellar turbulence, vrel
is higher for a lower gas density
and a larger grain radius (Yan+2004)
Hirashita & Yan+2009

These processes do not reduce dust
mass but change size distribution

coagulation

・ timescale of shattering, τshat
τshat ~ 1 (τSF / Gyr)1/2 yr

Sirono+2013## grain-grain collision processes## becomes efficient once dust## grains are enriched sufficiently

2-7. Dust evolution model (1)‐one-zone closed-box galaxy model (no inflow and no outflow)‐star formation rate (SFR)
Schmidt law with n = 1: SFR(t) = Mgas(t)/τSF with τSF = 5 Gyr‐initial mass function (IMF)
Salpeter IMF: φ(m) = m-q with q=2.35 for Mstar = 0.1-100 Msun
‐two dust species
graphite (carbonaceous grains)astronomical silicate (silicate and the other grains species)‐two-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
➜ ηWNM = ηCNM = 0.5

2-8. Dust evolution model (2)‐mass evolution of dust 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

3-1. Evolution of extinction curves in galaxies
dust amount

grain size distribution

extinction curve

MRN

Asano, Takeuchi, Hirashita, TN+13, MNRAS, 432, 637
Asano, Takeuchi, Hirashita, TN+14, MNRAS, 440, 134‐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3-2. Reproducing the MW extinction curve
steep extinction curve is due to thepresence of too much small grains

WNM=0.5
CNM=0.3
MC=0.2‐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

3-3. Extinction curves in high-z quasars
SDSS J1048+4637 at z=6.2 :broad absorption line (BAL) quasars

Hirashita+2008

Maiolino+2004, Nature, 431, 533➔ interstellar dust in the early
universe is SN origin?

Gallerani+10

3-4. A large amount of dust in high-z quasars

Calura+2014‐Huge amounts of dust grains are observed for the host galaxies ofquasars at z < 5➜ it is suggested that the grain growth is needed to account forsuch massive dust contents## it seems only the contribution of dust from SNe II cannot explain## the observed amount of dust grains in high-z quasars

How can we explain the dust mass and unusual extinction
curves observed for high-z quasars in a consistent way?

3-5. Explaining the high-z extinction curves
high-z quasar host: starburst galaxies➜ indicating a high fraction of MC
cf. MH2/MH ~ 5 from observations‐two-phase ISM: WNM and MC‐τSF = 0.5 Gyr‐amorphous carbon & silicate

Asano, TN, Hirashita, Takeuchi, 2014 in prep.

4-1. ALMA reveals dust formed in SN 1987A
SNe II-P

SED of 25-years old SN 1987A

Nozawa+07

Indebetouw+2014

ALMA spatially resolves cool(~20K) dust of ~0.5 Msun formed inthe ejecta of SN 1987A➔ SNe could be production
factories of dust grains

4-2. Dependence of dust radii on SN type
SN IIbSN II-P0.01 μm－ condensation time of dust
300-700 d after explosion－ the radius of dust formedin H-stripped SNe is small－ total mass of dust formed
・ 0.167 Msun in SN IIb
・ 0.1-1 Msun in SN II-P・ SN IIb without massive
H-env ➔ adust < 0.01 μm

Nozawa+10, ApJ, 713, 356

・ SN II-P with massive
H-env ➔ adust > 0.01 μm

4-3. Destruction of dust in Type IIb SNR
dust destruction in SNRs

gas density in SN IIb is muchsmaller than in SNe II-P
Nozawa+10, ApJ, 713, 356

Almost all of the newly formed
grains are finally destroyed inshocked gas➔ small radius of newly
formed dust
➔ early arrival of reverse
shock at the ejecta

4-4. Dust formation and evolution in SNe Ia
average radius

Nozawa+11, ApJ, 736, 45

dust destruction in SNRs
0.01 μm

・ condensation time :100-300 days
・ average radius of dust :aave <~ 0.01 μm
・ total dust mass :Mdust ~ 0.1 Msun

newly formed grains arecompletely destroyed for
ISM density of nH > 0.1 cm-3
➔ SNe Ia are unlikely to be
major sources of dust

5. Summary of this talkWe investigate the evolutions of grain size distribution
the extinction curve in galaxies‐ early phase : large grains (~0.1 μm) from SNe II and AGB stars➔ flat extinction curve‐ mid phase : small grains (<0.03 μm) via shattering/grain growth➔ steep extinction curve‐late phase : shift of peak of size distribution due to coagulation➔ making extinction curve flatter・ our model can explain the unusual extinction curve and large
amounts of dust grains observed for high-z quasars➜ a large fraction of molecular clouds, silicate and am.C・ envelope-stripped SNe (Type IIb, Ib Ia SNe) are not likely to bemain sources of dust