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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