Mullard Space Science Laboratory

Gaia/JASMINE 時代の銀河系考古学のための数値シミュレーション
Daisuke Kawata(Mullard Space Science Laboratory (MSSL), University College London (UCL))
Junichi Baba (NAOJ), Rob Grand (MPA fellow), Jason Hunt (Flatiron/CCA)
Jo (Ioana) Ciucă (MSSL, UCL→Astro3D fellow @ ANU)

Gaia Revolution!
Gaia: precise position/distance and motion of about 1 billion stars
in the Milky Way!

ESA/Gaia/DPAC
Gaia Early Data Release 3

Galactic archaeology
Motion and stellar populations (mass, temperature,metallicities and age) of stars in the Milky Way

Theoretical models
Numerical simulations+ Ground-based photometric spectroscopic surveys+ Asteroseismology from Kepler, K2, TESS, PLATO

4D2U/Saitoh

Where are we from? How did our Milky Way form?

Galactic archaeology
Motion and stellar populations (mass, temperature,metallicities and age) of stars in the Milky Way

Theoretical models
Numerical simulations+ Ground-based photometric spectroscopic surveys+ Asteroseismology from Kepler, K2, TESS, PLATO

4D2U/Saitoh

Where are we from? How did our Milky Way form?

Counter-rotating (?) low [α/Fe] halo stars
from a SMC-size galaxy last major merger at ~10 Gyr ago?
Gaia Enceladus! (Helmi et al. 2018)
Mainly fromSNe Ia (~Gyr)

0.4

L/Lsun[α/Fe]

disk stars

0.2

O, Mg…
SNeII (~Myr)counterrotating

less boundhalo stars

0-2

E/EsunHelmi et al. (2018, Nature)
See also
Belokurov et al. (2018) for a DR1 feature
known as Gaia Sausage,Brook, Kawata et al. (2003) withHipparcos data.

APOGEE/Gaia

Daisuke Kawata (MSSL, UCL)

-10

[Fe/H]

Credit: ESA, NASA, Koppelman,
Villalobos and Helmi,

Sausage & Mash!
Grand, Kawata et al.
(2020)

z=1.4z=1.3

Gaia Enceladus (akaSausage) was likely to
be a gas-rich merger
and make mash, i.e.
halo and thick disk!

Auriga cosmologicalsimulation (Grand et al. 2017,~30 Milky Way-sized galaxy
simulations with AREPO)

Daisuke Kawata (MSSL, UCL)

z=0.9

z=0

Early gas-rich mergers, turbulent small thick disk ⇒ Later inside-out thin disk formation(Brook, Kawata et al. 2004, Grand, …, Kawata et al. 2018)

Grand et al.
(2018)
Aurigasimulation

z=1.67z=1.04z=0.64z=0.38

Early violent star formation
Later inside-out growth ofDaisuke Kawata (MSSL, UCL)
with mergers.
the thin disk at the later epoch.

Two pathways of thick/thin disk formation (Grand et al. 2018, see also Noguchi 2018)
Auriga simulation: Grand et al. (2018)[α/Fe][α/Fe]

0.2
0.1
0.0-0.5 0.0 0.5[Fe/H]-0.5 0.0 0.5[Fe/H]

Inner disk
compact thick disk → metal rich thin disk
[α/Fe]
0.4-0.5 0.0 0.5-0.5 0.0 0.5[Fe/H][Fe/H]
outer disk
later metal poor disk from the accreted gas+ high [α/Fe] thick disk radial migration from inner disk
Observation:
Hayden et al.
(2015)

High-[α/Fe]
thick
low-[α/Fe]
thin

0.0
-1.0

0.0

-1.0

0.0

-1.0

0.0

-1.0

0.0

-1.0

0.0

[Fe/H]GES merger end of thick disc phase followed by inside-out thin disc formation?
Observational data: Gaia+APOGEE: Ciucă, Kawata et al. (2021)
consistent with simulations in Brook et al. (2004, 2012), Grand et al. (2018, 2020)!
high-αthick

end ofGES
merger?
Gaia+SDSS/APOGEE
spec survey datawith neural network
trained age.
Ciucă et al. (2021)

Well-mixed thick disk

Bridgeouter

Metallicity gradientbuilds up ⟸ inside-outlow-α
thin
inner

younger
wider [Fe/H]

Inner disk
continuous
star formation

Outer low-[Fe/H]
stars forms
after thin disklarge enough Outer

inner

outer

Observation at ~ Rsun

innerage(Gyr)Thick disk formation in action? high-z (z>1) disk are kinematically hot?

Observation

Local HI
ALMA [CII]V/σ

10Rizzo et al. (2020)

0redshift45

KMOS3D (Hα)
Wisnioski et al. (2015)

Need for self-consistent high-resolution simulations with gas and star formation
to resolve the gas-rich mergers at high-z and thick and thin disk chemo-dynamical structures at z=0.

Back to Solar neighbourhood kinematics
revealed by Gaia…

Daisuke Kawata (MSSL, UCL)Rotation

Stellar velocity distribution in the solar neighbourhood
Many velocity ~ km/s scale structures!
Gaia DR2

fasterComa Berenices
HyadesRotation velocity V (km/s)

VU
Sun

SiriusHerculesPleiadesArcturusoutwardinwardslowerGalactocentric radial velocity U (km/s)

Antoja et al. (2018)
Phase spiral

Gaia Collaboration, Katz et al. (2018)

Sagittarius dwarf impacting the Galactic disk?
e.g. Gómez et al. (2013), Laporte et al. (2017, 2018)
Disk response to the perturbation⇒ Galactoseismology ⇒ disk and halo mass.

A. Smith

However, required mass of theperturbed (~5x1010 M⊙), muchheavier than Sgr. (~108 M⊙)(Bland-Hawthorn, TepperGarcía 2019,Bennett & Bovy 2021).
ESA
Daisuke Kawata(MSSL,UCL)(2018)
Antojaet al.

Need a better model?

Bar pattern speed slower than pre-Gaia belief, and even slowing down?

Ωb (km/s/kpc)

404Gaia + APOGEE
Bovy et al. (2019)

8R (kpc)

Vrot (km/s)

Chiba, Friske, Schönrich(2021a,b)

Daisuke Kawata (MSSL, UCL)

Vrad (km/s)

Slow-down bar due todynamical friction?
⇒ Nature of dark matter.
CDM, ULDM, MOND, MOG

Remaining question: The epoch and impact of the bar formation?
Hierarchical clustering at
the early Universe

Baba & Kawata(2020)GALACTICNUCLEUS

The burst of star formation in the cold nuclear disk (NSD)= the formation epoch of the Galactic bar
Bar formation epoch ~ Age of NSD
Impact to radial migration of the Sun?
⇐ JASMINE NIR astrometry mission by ISAS/JAXA, NAOJ
the Gaia-level astrometry for the Galactic centre stars.

JASMINENSD: Link to first galaxies?

Nishiyama et al.

NSD

Nuclear Stellar Disk
(NSD ~109 M⊙)

120’~280 pc
Nuclear Star
Cluster (NSC)JASMINE (precise astrometry for bright stars) &SUBARU ULTIMATE (faint stars populations andmotion with JASMINE reference frame) synergy.
Kikuchihara et al. (2020)

Self-consistent high-resolution simulationsof the Milky Way-like galaxies with different formation histories?
• Questions• Remnant of the first galaxy and ancient mergers?
• Thick disk formation vs. high-z cold gas disk. Thickdisk formed as thick or heated up?
• Galactic bar formation: when and the impact.
• Bar slow down? Disk corrugation?
Galactoseismology, nature of dark matter• How the Sun migrated from the inner disk?
• Need for simulations to resolve• z>6 first galaxy formation• high-z gas-rich mergers, cold and ionized gas disk.
• Chemodynamical-structure from NSD, thick andthin disk and the remnant of the ancient mergers.
• a few km/s scale perturbation.
• ~ a few 10 Myr outputs• Variety of formation and evolution histories

Auriga suit (Grand et al. 2017)