6th Galaxy Evolution Workshop (2019)@ U. Tokyo on 6th of June, 2019

Galaxy simulation with theevolution of grain size distribution
Shohei Aoyama

Academia Sinica (ASIAA)

Collaborators: Hiroyuki Hirashita (ASIAA), Kentaro Nagamine (Osaka U.)

Based on Aoyama et al. MNRAS submitted (2019b)

arXiv: 1906.01917

Introduction• Dust grains are essential for star formation and understanding the extinctionof UV. ( Ms. S. Nagasaki’s talks )• Hydro-dynamical simulations are a very powerful tool to reveal ISM physics.

SED

SED of M31

Groves+2012

S. Aoyama+2017

Introduction• Evolution of dust size distribution is essential for understanding observations.
( e.g. Asano et al. 2013b, 2014, Hirashita 2015, S. Aoyama+17 (A17), 18, 19a )• Reduction of computational cost (optimization) is crucial forhydro-dynamical simulations.
Distribution fcn.

1 year
1 day

isolate CosmologicalgalaxyN=2×5123

One zone
Hirashita & S. Aoyama (2019)

Cosmological10243

Private communication to a collaborator of R. S. Asano

Two size approximation (Hirashita 2015)(See also S. Aoyama+17 (A17), 18, 19a, K-C Hou+17, 19 )• Grain size distribution are represented as two modes (Large, Small).
• Grain-Grain interaction (shattering, coagulation) can be implemented
in the simplest way.

Hirashita & SA (19)Two size approximation (Hirashita 2015)(See also S. Aoyama+17 (A17), 18, 19a, K-C Hou+17, 19 )• Many observed quantities can be explained by two size approximation.
• The evolution of spatial distribution of grain distribution is also available.

Extinction curve
MW extinction
Curve (Pei 1992)

Radial profile ofdust surface density around gals.
● Observation(Menard+10)

w/ size dist.
S. Aoyama+18
w/o size dist.
McKinnon+17
K-C Hou, S. Aoyama et al. (2017)

Full grain size distribution(Asano+13b, 14, McKinnon+18, Hirashita & S. Aoyama 19)• In reality, dust grains has continuous distribution from 0.3 nm to 3 μm.
• Grain growth/destruction can be described as communication
between different size bins.

Hirashita & SA (19)

Full grain size distribution(Asano+13b, 14, McKinnon+18, Hirashita & S. Aoyama 19)• They firstly implemented the evolution offull size distribution into hydro-dynamical
simulations (mesh).

McKinnon et al. (2018)

Calculation cost

• Our model works even in the simulations with 16 grid points.
( Hirashita & S. Aoyama 2019 )• Remark Tcal∝Nbin2• We use 32 grid points for describing grain size distribution.
Extinction curve of a MW-like galaxy

1 year
1 day

isolategalaxyTypicalerror-barHirashita & S. Aoyama (2019)

One zone

Simulation setup• Dust module has been remodeled in Hirashita & S. Aoyama 19.
• The dust module is implemented into GADGET3-Osaka (Shimizu+19).
• We performed a simulations with an isolate spiral galaxy.

Initial condition (AGORA project; Kim+16)MW-like galaxy (Mtot~1012 M☉)• Ngas=105• Ndm=105• mgas= 8.59×104 M☉• mdm =1.25×107 M☉• softening length εgrav=80 pc

Distribution of Gas particles

Time evolutions of dust-to-gas mass ratio• t ≲ 0.3 Gyr, the stellar dust
production (Dtot = finZ).
• t ≳ 1 Gyr, asymptoticallyapproaching to Dtot = Z.
(Same trend of A17)
• S. Aoyama+17 over-predicts
accretion at metallicity Z< 0.1 Z☉.
(Different trend of A17)
a risk in the two-size distribution

Datapoints: Remy-Ruyer et al.(2014)& Zhukovska (2014)

Time evolutions of size distribution of grains

Time evolutions of extinction curves
The median in the diffuse
medium (t = 3 Gyr) broadly
explains the Milky Way
extinction curve (Pei 1992).
It suggests that there are
massive galaxies at z=2(tage≃3Gyr) that havea Milky-Way-like extinction.

Radial dependence of extinction curves

The trend of the radial dependence of extinction curve isthe same as a previous work (Hou et al. 17)
Extinction curve at 3 kpc < R < 5 kpc at 3 Gyr is responsible forobservational one (Pei 1992).

outercentercenterouterComparison with observations:Categorization of galaxies

sSFR

Category

10 Gyr-1 < sSFRIsSFR < 1 Gyr-1

III

1 Gyr-1 < sSFR < 10 Gyr-1 II

Category I
Category II

Category III

Radial profile of the dust-to-gas ratio
We can explain a typicalgalaxy’s behavior.
-> not only dust size but
also dust transport isalso solved similarly as
observational ones.
• R25 : the radius at whichsurface brightness falls to
25 mag arcsec-2• R25≃4 R* (Elmegreen 1998)≃7 kpc (in this simulation)

Datapoints: Mattsson & Andersen (2012)

Radial profile of the dust-to-metal ratio• Broadly consistent
with the observational
data t=1 Gyr.
• Over-prediction
dust-to-metal at large
radii because the• R25 : the radius at which
effect of accretion tosurface brightness falls to larger radii at t= 3Gyr.
-2
25 mag arcsec• R25≃4 R* (Elmegreen 1998)≃7 kpc (in this simulation)

Future prospect: Cosmological simulations

isolategalaxy

One zone

Cosmological
N=2×5123

Cosmological10243

Summary• We have implemented full size distribution into SPH simulations
and investigated spatially resolved evolution.
• We reproduced observational results (extinction curves, radial
distribution of Dtot)• Many of results based on the two-size approximation can be justified
based on full size distribution treatments.
• Extinction curves similar to Milky Way can be found in z≃2 Universe.
• However risks for adopting two-size approx. are also found.