銀河考古学:近傍銀河宇宙から探る銀河形成史

Galactic Archaeology:Deciphering formation histories of galaxies from the local universe

千葉柾司（東北大学）

Masashi Chiba(Tohoku Univ)

1

Milky Way

AndromedaSendai

Local Universe

Our Galaxy

Understanding stellar populations Formation and evolution of the Galaxy

high-z universe(snapshots of various galaxies)

stellar systemin local universe(tracing evolution of a galaxy)

Bekki & Chiba 2001

Galaxy formationand evolution

complementary

gasstars

Galactic astronomy based on resolved stellar system

• Photometry ⇒ magnitude, color (→ color-magnitude diagram : CMD）

• Spectroscopy ⇒ metallicity (→ age), chemical abundance pattern (→ star formation history & chemical evolution), radial velocity

• Astrometry ⇒ proper motion & distance (→ information on 6-dimensional phase space)

Spatial structure, dynamical structure,star formation, and chemical evolution

of the stellar system⇒ galaxy formation and evolution

Old galactic components

inner halo outer halo

globular clusterhalo star

thick disk

Thin disk : age < 10 GyrThick disk, Halo : age > 10 GyrBulge : age ~ 10 Gyr

bulge

CMD of the globular cluster : M3

TO

RGBHBAGB

SG

V

B－V

Formation history of a globular cluster

BS

MS

Fossil records of galaxy formation⇒ Galactic Archaeology

The Sun

9

Cosmic star formation historyMadau & Dickinson (2014)

Star Formation Rate Density evolution Stellar Mass Density evolution

Milky Way & Galactic satellites

10

Local Group

11

HST photometry of LG galaxies

Leo I (dSph)

Stream

Northern Spur

G1 ClumpM32

Andromeda GalaxySubstructure in M31’s halo

(Ferguson et al. 2002)

14

ACS/HST photometry of M31’s halo(using 120 HST orbits!)

V=30mag

V=28mag

Comparison with ΛCDM model

Halo realization 1 16

Halo formation model (Bullock & Johnston 2005)merging tree + semi-analytic galaxy formation

Chapters

1. Kinematics and dynamics of a stellar system2. Stellar populations and chemical evolution3. The nature of Galactic components4. Galactic dark matter5. Formation of the Galaxy6. Formation and evolution of Local Group

galaxies

17

References

• Galactic Dynamics (2008) by Binney & Tremaine (Princeton)

• Nucleosynthesis and Chemical Evolution of Galaxies (1997) by Pagel (Cambridge)

• Evolution of Stars and Stellar Populations (2005) by Salaris & Cassisi (Wiley)

• シリーズ現代の天文学

４：銀河Ｉ, ５：銀河ＩＩ, ７：恒星 (日本評論社)• 銀河考古学（Galactic Archaeology）（2015）

by 千葉 （日本評論社） 18