Influence of the gas infall on
dust evolution in galaxies
Sayaka K. Nagasaki (Nagoya Univ.)
Tsutomu T. Takeuchi、Ryosuke S. Asano（Nagoya Univ.）

Introduction
Dust influence the various physical properties of galaxies
Dust absorb the stellar lightand re-emit at the Infrared
Stars

Catalytic reaction on the surface
HUV

Dust

DustIR

The spectral energy distribution(SED) of galaxies are changed

H

Raise star formation rate (SFR)

The amount of dust and size distribution is important tounderstand galaxies.
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

1 15Observational motivation
First galaxies are formed between 500 million and 900 million years after
the big bang which correspond to between redshift 6 and 10
z = 6 - 10

First galaxies form

NAOJ

Recently dusty galaxies located at these high redshift have observed by
ALMA
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Observational motivation•

A1689-zD1 (Watson et al. 2015)
redshift = 7.5

M* = 1.7 × 109 M⊙

Mdust = 4 × 107 M⊙•

A2744-YD4 (Laporte et al. 2017)
redshift = 8.36

M* = 1.97 × 109 M⊙

Mdust = 5.5 × 106 M⊙

Despite the early galaxy formation stage,these galaxies get huge amounts of dust (> 106 M⦿)
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Big problem of high-redshift galaxies

What is the origin of dust in early universe ?

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Big problem of high-redshift galaxies

What is the origin of dust in early universe ?

One possible answer might be“Gas infall”

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Existence of gas infall• Galaxies are formed by infalling gas from the IGM

Schaye et al. 2019

• Previous research：Closed box model (e.g. Asano et al. 2013)• Total baryonic mass is provided initially• The effect of gas Infall on the dust evolution is still uncertain
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Aim of our research
Investigate the influence of the gas infall
on dust evolution in galaxies
Asano model (Asano et al. 2013a, b, 2014)

Closed box model → Gas infall model

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Method
We use Asano model for calculating chemical evolution of dust
What is Asano model ?
• Chemical evolution model of dust in galaxies• It considers 4 components (ISM, stars, metal and dust)

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Asano modelBasic equation
ISM
Stars
MetaldMISM(t)= − SFR(t) + R(t)dtdM*(t)= SFR(t) − R(t)dtdMz(t)dt= − Z(t)SFR(t) + YZ(t) + RZ(t)R: returned mass from dying stars

Z(t) ≡ Mmetal /MISM : metallicity

YZ: metal supply by dying stars

Star formation rate (SFR) is described byMISM (t)SFR(t) =⌧SF

τSF : star formation timescale

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

8 15

Asano model
Dust evolution processes
Grain growthby metal accretion

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

9 15

Asano model with gas infall
Difference between this research and original Asanomodel• We consider the gas infall instead of closed box
MtotalI(t) =exp(−t/τin )τinfallτinfall : infall timescale
MtotalInfall rate

• Infall rate is described by (Inoue 2011): total infall massgalaxy age

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Asano model with gas infall
Basic equation
ISMStarsMetaldMISM(t)= − SFR(t) + R(t)dtdM*(t)= SFR(t) − R(t)dtdMz(t)dt+ I(t)= − Z(t)SFR(t) + YZ(t) + RZ(t)R: returned mass from dying stars

Z(t) ≡ Mmetal /MISM : metallicity

YZ: metal supply by dying stars

Star formation rate (SFR) is described byMISM (t)SFR(t) =⌧SF

τSF : star formation timescale

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Result : Mdust-Mstar ratio
We investigate the effect of varying gas infall timescale
Parameter setting
10

Mfinal = 2 × 10

M⊙

(Mfinal =final total galaxy mass )τSF = 0.5 Gyrτinfall = {1 Gyr, 5 Gyr}

Compared to the closed box
model, infall model can supply
more dust even for smaller
stellar mass
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

12 15

The mechanism of dust supply
Dust

Despite the difference in infall
timescale, nonlinear growth of dust inthe same epochgalaxy age [Myr]Stars

However, resultant stellar
masses sredifficult

galaxy age [Myr]Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/1213 15

The mechanism of dust supply
Dust

Stars

Compared to the closed box model, infall model can supply more dust
even for smaller stellar mass
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Comparison with high redshift galaxies
Watson et al. (2015)

Laporte et al. (2017)• We can explain the observation of Laporte et al.(2017)• We still cannot explain the observation of Watson et al. (2015)
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Possible scenario for Watson et al. (2015)
The estimation of dust temperature (35K) which is used for estimating
dust mass might not be correct.
Equation of dust mass
D 2Sν
Md =κνB(ν, Td)

1000

Flux (μJy)

1001010.1•

Watson et al. (2015)

0.01
1

10100

Sν : Flux at frequency νκν : Dust mass absorption coefficient at ν
D : DistanceB(ν, Td) : Modified black body1000

observed wavelength (μm)

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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The dependency of dust temperature
35K
50 K
75 K(typical value)• Very hot dust ( > 75 K) is required to explain the observation
Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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Summary• We investigate the effect of gas infall on the dust evolution• Infall model can supply sufficient amount of dust with smaller
stellar mass compared to the closed box model• Very hot dust is required to explain the observation of Watson
et al. (2015)

Sayaka NAGASAKI

初代星・初代銀河研究会

2019/11/12

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