Chap.6 Formation and evolution ofLocal Group galaxies• Properties of Local Group galaxies• New aspects of Magellanic Clouds• Formation of satellite galaxies• New insights into the missing satellites problem• Formation of the Andromeda galaxy1

6.1 Properties of Local Group galaxies
Milky Way and satellite galaxies2Local Group

3

MW

M31

isolated4

Dwarf galaxies

Leo I

Carinaeffective radiusdwarf spheroidal galaxies（dSphs 矮小楕円体銀河）-18mag5Structures of various types of galaxies(Tolstoy+09, ARAA, 47, 371)

Half-light radiusV-band surface brightness

Classical dwarf satellites M_V < -8 mag
Ultra Faint Dwarfs (UFDs) M_V > -8 mag

dwarf galaxies:Mv > -17 and more spatially extended
than globular clusters
with gas: dIrr, without gas: dSph

66.2 New aspects of Magellanic Clouds

50kpc
LMC(previously thought)

M~2x1010Msun

62kpc
SMC

M~2x109Msun

Most likely orbit of LMC/SMC
to reproduce Magellanic Stream(Diaz & Bekki 2012)
At least 2 pericentric passages
over the past 4Gyrs

Magellanic Stream (HI)LMC/SMC’s orbit
Recent severalworks (Gaia, HST)
suggestthe first infall ofLMC/SMC

traditional model

The case ofFirst Infall
Besla+ 2010

Likely orbits of LMC/SMC + satellites
using Gaia DR2: Patel et al. (2020)

Misaligned Orphan Stream~effect of the very massive LMC?~
Erkal et al. 2019 (using Gaia DR2 PMs)
Points:RR Lyraealong OS11

“Field of Streams” and new satellites
in SDSS data (Belokurov et al. 2006)12

Misaligned Orphan Stream~effect of the very massive LMC?~
Erkal et al. 2019 (using Gaia DR2 PMs)Best fit MLMC
~ 1.38x1011 Msun
An order of magnitude
more massive thanpreviously thought!

13

Wake effect of the massive LMC
on MW’s dark halo?
If MLMC ~ 1011 Msun
following recent results with Gaia
LMCEffects on dark matter distribution in MW(Garavito-Camargo et al. 2019)Garavito-Camargo et al. 2021

6.3 Formation of satellite galaxies

HST photometry of satellite galaxies

16Leo I @ D=260kpc

Low SFR
lasting over ~10Gyr
Metallicity & Age
are degenerated
Spectroscopy
17Fornax @ D=138 kpc
Buonanno+ 1999
(from HST image)de Boer+2012(from CTIO image)[Fe/H]=-0.7

18HST/WFPC2 results(Weisz et al. 2014)

Varieties in SF histories

19

Long-term orbital motions of Galactic satellites
in the growing mass of the Galactic halo
(Miyoshi & Chiba 2020)
Classical dSphs (MV < -8)

Orbits using Gaia DR2
Draco

Look back time

UFDs (MV > -8)

FornaxComparison
between a
fixed andevolving MW
potential(different att > 4 Gyr)

Look back timeLong-term orbital motions of Galactic satellites
in the growing mass of the Galactic halo
(Miyoshi & Chiba 2020)
Virial radiusClassical dwarfs(MV < -8)

Ultra-faint dwarfs(UFDs)(MV > -8)

DracoFornax

Miyoshi & Chiba 2020

Starformation
history

Orbitalevolution

Virial radius of
the MW’s halo

Leo IStar
formation
history

Orbitalevolution

Ursa MinorFirst infall timecrossing virial radius= time of SF peak(Star formation
trigged by tidal effect+ ram-pressure)UFDs
Miyoshi & Chiba 2020

Star
formation
history

Orbitalevolution

Virial radius of
the MW’s halo

- 1st SF ended before the 1st infall and 2nd/3rd SF can be related to the infall- What is the relation with r-process element production?

Satellites’ orbits vs. SF histories~ evidence for environmental effects ~Miyoshi & Chiba 2020

Fraction of stars
formed afterSF peakSF is suppressed morefor smaller pericentric
radius at fist passage

Pericenter at first passage (kpc)

Metallicity vs. luminosity relation

UFDs appear to show different metallicities

25[/Fe] ratios in several classical dSphs(Tolstoy+ 2009)26

List of known UFD galaxies

27

HST results by Brown+2012
UFDs are very old systems (as old as M92)

Synchronization of SF truncation within ~1 Gyr ?

Kirby+ 08
Assembly of the stars inultra-faint dwarf galaxies
reproduces the MW halo

Tolstoy +08
UFDs show similarabundance pattern tothe metal-poor MW halo29

R-process enrichment in UFDs
Reticulum II: Ji et al. (2016)

Solar r-process
Solar s-process

An event of NS mergers is suggested.

30

NS mergers and chemical evolution
Wanajo, Hirai, Prantzos (2021)

Chemical evolution of halo building blocks
Delay time distribution

31

Cosmological zoom-in simulation for galaxy formationand origin of r-process enhanced stars
Hirai, Bees, Chiba, et al. (2022)
UFD galaxy
as a site ofr-processenrichment[Eu/Fe]>0.7: r-II
Created at t < 4 Gyr6.4 Formation of the Andromeda galaxy

Andromeda Halo
(Ferguson et al. 2002)

Northern Spur

N205

M32

G1 Clump
Stream33

Stellar halos in M31/M33
Northern Spur

M31

North Western Stream

G1 Clump
Giant Southern Stream

M33
Martin et al. 2013

Structure of the M31 halo
(Tanaka, Chiba et al. 2010)
Stream field
Stream F
80kpc

NW

Stream E

Stream D
Stream C streamSE

50kpc
27kpc
50kpc
80kpc

RGB stars with
I0<24, V0<24.8-1.71<[Fe/H]<-0.71

Tip of RGB

AGB bump
Red clump(Photometric) metallicity distribution ofGiant Southern Stream36

Progenitor: disk galaxy
with metallicity gradient

Numerical simulation of GSS
Hotta, Mori, Otaki, & Kirihara in prep

GSS (receding from us)

Metal-poor( Fe/H < −1.0)

Rich( Fe/H ＞ − 1.0)

New stream

This metal poor, faint, and positive velocity stream
at the eastern side of GSS is missing in DESI map.
37

Los velocities (wrt. M31)

Dey et al. (2023) with DESI
Machine-learning selection ofvery red, metal-rich, bright RGBs
2 < (g-i) < 4, z < 21.5 mag

Complicated selection function
Biased for very metal-rich stars( -0.5 < [Fe/H] < +0.5)

Los velocities (wrt. M31)

GSS

Phase-space diagram

Metal-poor substructures
are entirely disappeared!

GSS
approaching to usImportant features in CM diagram• RGB bump (RGBb)– Evolutionary pause when the H-burning
shell crosses a discontinuity left by theconvective envelope• Tip of RGB (TRGB)– He-burning ignition through the He flash– Nearly constant I-band mag ⇒ standardcandle– 843±48kpc, 855±48kpc ＞ D=770kpc• Red Clump (RC)– Clustered feature of red HB (He coreburning) stars being metal-rich / young age• AGB bump (AGBb)

Luminosities of RGBb, RC,– Clustered feature of AGB stars at thebeginning of He shell-burning evolution & AGBb depend on age.

⇒ age distribution

39

Alves & Sarajedini 1999
AGBb
RGBb
HB

FainterforZ↑M↓

Age indicator40Age calibration for giant stream

Mean Age ～ 7.1 Gyr
Tanaka+2010

41

North Western Stream
North Western Stream

Subaru/HSC data

Komiyama, Chiba et al.2018

MW disk
MW halo streami

M31’s Red Clumpg-i

Komiyama et sl.2018

North Western Stream

NB515-g

NB-selected RGBs

RGBs

g-i

Red Clump stars

Formation of the NW stream• Progenitor of the NW stream– Satellite withYohei Miki(U. Tokyo)• Interaction with a subhalo– Mass:– Test orbit: 2 circular orbits with(orbit 0, orbit 1)• LOS velocity fields after 300 Myr• Effect of a subhalo mass,

True size of Andromeda
M31（アンドロメダ銀河）の真の大きさ
M31

M31ハロー

M31ハロー
M31

Future Prospects

Major telescopes/instruments
SubaruHSC
PFS：2024Ultimate:

Vera C.
Rubin(LSST)
2023-

TMT

ALMA

Gaia

JASMINENIR astrometry
Late 2020

WFOS
HROS
NIRES
2028?

JWST
NIRCamNIRSpec
MIRI
2022-

EuclidYJH
2023-

Nancy Grace
Roman Space
Telescope(WFIRST)
2026-

Subaru/PFS(Prime Focus Spectrograph)
FOV: 1.3 deg in diameter2400 fiber positioners
λ: 380~1,300 nm(3 channels: Blue, Red, IR)
R: ~3,000 (LR), 5,000 (MR)
Scientific run: 2024 ~International collaboration:
IPMU (U. of Tokyo) & NAOJ/Subaru+ Caltech/JPL, Princeton, JHU, LAM,Taiwan, UK, Brazil, China

Science in 3 main areas- Cosmology, Distant Galaxies, Galactic Archaeology

TMT(Thirty Meter Telescope)
WFOS, IRIS, IRMS,HROS, NIRES etc.
R~5,000 for mV<26 mag
R~50,000 for mV<21 mag
First light: 2028~?

Goal: ultimate understanding of galaxy formation
based on resolved stars in the local universe

M31/M33’s halo survey with PFS
MWdisk

M31
RGB

MW
halo

WFOS

200～400 RGBs/field with PFS

MWdwarfs

TMT/WFOSM31 has the [α/Fe] bimodality ?
PNe: O/Ar ratio measurements (Arnaboldi et al. 2022)

34% of Ar comes from SNe Ia[ɑ/Fe] in stars
JWST/NIRSpec(Nidever et al.)to scale⇒ nobimodality (?)

Milky Way disks
JWSTM31 has the [α/Fe] bimodality ?
O/Ar ratio from PNe(Arnaboldi et al. 2022)

34% of Ar comes from SNe Ia[ɑ/Fe] in stars
JWST/NIRSpec(Nidever et al.)to scaleJWST

Our PFS survey will cover larger disk areas toclarify this bimodality for understanding disk
formation process

Nearby groupof galaxies

6 Mpc
N5128 Group
Canes I Group

Sculptor GroupLocal Group

M81 Group
Mafferi GroupStellar halos from numerical simulation～reflecting different merging histories～

Cooper et al. 2010

NGC 55 @ Sculptor group D=2.1Mpc(Tanaka, Chiba, Komiyama, Guhathakurta & Kalirai 2011)[Fe/H]

Taken from Subaru/S-Cam image

M31
Thick disk
NGC55
HaloZ (kpc)

Deep imaging w. Subaru + medium
resolution spectra with TMT/WFOS⇒ stellar age, abundance and velocity

M81 @ M81 group D=3.6Mpc(Subaru/SuprimeCam: Barker+ 2009)M81 @ M81 group D=3.6Mpc(Okamoto et al. 2015)

HSC image

Deep imaging w. HSC + medium resolution spectra with TMT/WFOS⇒ stellar age, abundance and velocity

Nearby elliptical galaxies
NGC5128 (Cen A)

DEC=-43
D=3.6Mpc

Peng+ 2002 (Blanco T.)

Harris+ 1999 (HST)

Deep imaging + medium
resolution spectra with TMT/WFOS⇒ stellar age, abundance and velocity

Conclusions
SubaruHSC
PFS：2024Ultimate:

Vera C.
Rubin(LSST)
2023-

TMT

ALMA

Gaia

WFOS
HROS
NIRES
2028?

JWST
NIRCamNIRSpec
MIRI
2023-

JASMINENIR astrometry
Late 2020

Very promising future prospects!

EuclidYJH
2023-

Nancy Grace
Roman Space
Telescope(WFIRST)2026-