New Dust Evolution Modelin Galaxies
with Gas Infall
Sayaka K. Nagasaki (Nagoya Univ.)
Tsutomu T. Takeuchi
Ryosuke S. AsanoIntroduction• Dust is small particles which inﬂuence the various
physical properties of galaxies• Emission from stars in galaxies is aﬀected by dust
absorption and re-emission
StarsUV

Dust

IR• The amount of stellar light that dust absorbs and re-emits
depend on the quantity and size distribution of dust

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The origin of dust

These components of galaxies are linked each othermolecular gasstar

dust / metal

Composition evolution of galaxies

Chemical evolution
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Chemical evolution of dust

Dust mass [M⦿]

Asano et al. (2013) have developed the model toexplain the dust evolution (Asano model)
108

107

106
1091010

Stellar mass [M⦿]

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Chemical evolution of dust

Dust mass [M⦿]

Asano et al. (2013) have developed the model toexplain the dust evolution (Asano model)
108②Rapid growth in the ISM

107①Ejection from AGB stars or SNe II

106
1091010Stellar mass [M⦿]

Problem1011

old• The mechanism of dust supply at high redshift is still
unknown !!

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Dusty galaxies at high redshift
For example,
we cannot explain the observation completely•

Lensed galaxy A1689-zD1 (Watson et al. 2015)z = 7.5
M* = 1.7 × 109 M⊙

Mdust = 4 × 107 M⊙•

Lensed galaxy A2744-YD4.
(Laporte et al. 2017)z = 8.38
M* = 1.97 × 109 M⊙
Mdust = 5.5 × 106 M⊙

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Dust mass [M⦿]1081071061091010

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Stellar mass [M⦿]

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Infall model
Dust mass [M⦿]

108

107

106
109

Stellar mass [M⦿]
1010

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• When we discuss the early stage of galaxies, we have toconsider how galaxies formed and evolved in their ﬁrst phase• Therefore, we introduced the gas infall to construct more
realistic evolution model for dust in galaxies

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Infall model

We adopted the following scenario (Inoue 2011)① Small galaxies are formed② The galaxies become larger and larger as they merge
with each other③ Galaxies also obtain mass by an accretion process
We simply assume a smooth exponential gas-infall rate

MinfalltI(t) =exp(− )τinτinSayaka Nagasaki

τin : infall time-scale
Minfall: total infall mass

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Method• We calculated the masses of these 4 components
dMISM(t)= − SFR(t) + R(t) + I(t)dt

ISMdM*(t)= SFR(t) − R(t)dtStarsdMz(t)Metaldt

Infall rate

Minfalltexp(− )τinτin= − Z(t)SFR(t) + YZ(t) + RZ(t)R : returned mass rate from dying stars
Z(t) ≡ Mmetal /MISM : metallicity

YZ : metal supplying rate by dying stars

Dust equation is slightly complicated . . .
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Method
Dust evolution processes

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Method
Dust evolution processes

increase the massdecrease the mass

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Method

Model assumption• ISM contains 2 phases-3
Warmneutral
medium(WNM):
6000K,0.3cm•• Cold neutral medium (CNM): 100K, 30 cm-3
• We adopted Schmidt law for the SFRfor n=1

ΣSFR ∝ ΣnISM

MISM (t)SFR(t) =⌧SF

τSF : star formation timescale
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Result : Z-D relation

Z-D relation is consistent with previous research

D ≡ Mdust /MISM

10-2

Non-Linear !!!

10-3

τinfallτinfallτinfall

10-4

10-2

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Z ≡ Mmetal /MISM [Z⊙]6th GEW 2019100

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Result : Mstar-Mdust ratio

Gas infall model seems to be better model comparedwith than the previous model

Dust mass [M⦿]

108

107

τinfallτinfallτinfall

106

109

1010

Stellar mass [M⦿]

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Discussion: Mstar-Mdust ratio
Infallmodel

Previousmodel

Rapidly growth of dust

Rapidly growth of dust

• If we consider the galaxy evolution due to gas infall,
the size of galaxies become larger as dust evolve• Dust can experience the rapid growth at lower stellar
masses

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Summary• Infall model can explain the formation of galaxy moreaccurately• The Z-D relation remains unchanged even if weintroduced a gas infall, and it is found to be consistent
with previous results• Dust can experience the rapidly growth at lower stellar
masses

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