Galactic archaeology

Rodrigo IbataObservatoire de Strasbourg

age in Gyr

mass

fra

ctio

nAbadi, Navarro, Steinmetz & Eke 2003

Fine structure of simulated galaxies

thin

dis

kth

ick

dis

ksp

hero

id

The big questions

● Where are/are there missing satellites?● Are dark matter profiles universal?● What is the fine distribution of dark

matter?● How did the galaxy build up?● What was the role of accretion in the

formation of the halo, disk, bulge?● What was the detailed chemical

enrichment history?

Uniqueness of the MW & Local Group

● Kinematic surveys of 1000s of stars possible

● dynamics of fine structure

● Detailed chemistry● (chemical tagging of stars?)

● Age-dating of stellar populations

Halo structure: streams!

J. Bullock

Halo streams

Majewski et al. 1994

Majewski et al. (2003)

SDSS colour-selected starsNewberg et al. (2001)

also SDSS RRLyraesIvezic et al.

Quest RRLyraesVivas et al.

Substructure in the disk: The Monoceros ring

SDSS: Newberg et al. (2002)

then Yanny et al. (2003), Ibata et al. (2003), Crane et al. (2003), Rocha-Pinto et al. (2004), Frinchaboy et al.

(2004), Peñarrubia et al. (2005)

• 120°<l<240°• |b|<30°, both hemispheres• 15 < DGC < 20 kpc• almost circular orbit• σvr ~ 20-30 km/s• several globular and open clusters coincide with orbit

➙ Accretion stream?

An accretion into the disk?

● Heliocentric distance:

– TRGB: 7.2 ± 0.3 kpc

● 4-10 Gyr population

● σ=12km/s

(Martin et al 2004, 2005,Bellazzini et al. 2005)

Outer galaxy in Red Clump stars

Canis Major

TriAnd

Monoceros Ring

G. Lewis

Blue RGB Red RGB1

25

kp

c

95 kpc

c.f. Andromeda...

Outer disk substructure

Qualitatively consistent with predictions (e.g. Abadi et al. 2003)

Missing satellites?

Klypin et al. (1999)Moore et al. (2000)

Bullock et al. (2000)Somerville (2001)

Stoehr et al. (2002)

Kravtsov et al. (2004)

Moore et al. 2000

New M31 satellites: Metal-poorNeighbors within 8”

And III

Neighbors within 2”

CFHT/MegaCam (Martin et al. 2006 in prep)

Neighbors within 12”Neighbors within 8”

New M31 satellites: Metal-rich

How can we detect completely dark structures?

By the heating of globular cluster streams!

No dark lumps lumpy DM halo

Ibata, Lewis, Irwin, Quinn (2002)

existence proof: Pal5

Pal5 : Odenkirchen et al (2001)Dehnen, simulation

GAIA

● ~1 billion stars surveyed to V~20

● proper motions: 10μas at V=15

● velocities for 108 stars (2-10km/s) to V=17

● ~10% accuracy parallaxes to 10kpc

● However, no chemical “finger-printing”

Chemical tagging...

Venn et al. 2004

Conclusions

● Studies of nearby galaxies are needed to test cosmological predictions on low-mass scales– dark matter distribution (cusps)

– existence of dark satellites

– detailed formation history of galaxies

● GAIA will revolutionise this field, but will lack detailed chemical information, as well as accurate radial velocities

● Chemistry (e.g., from ARGOS or WFMOS surveys) may prove to be key additional info to unravel the mess left after all the merging