Galactic archaeology

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Galactic archaeology

• Rodrigo Ibata
• Observatoire de Strasbourg

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Fine structure of simulated galaxies
Abadi, Navarro, Steinmetz Eke 2003
spheroid
mass fraction
thick disk
thin disk
age in Gyr
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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?

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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

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Halo structure streams!
J. Bullock
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Halo streams
Majewski et al. 1994
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Majewski et al. (2003)
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SDSS colour-selected stars Newberg et al.
(2001) also SDSS RRLyraes Ivezic et al.
Quest RRLyraes Vivas et al.
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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)
120ltllt240 blt30, both hemispheres 15 lt
DGC lt 20 kpc almost circular orbit svr
20-30 km/s several globular and open clusters
coincide with orbit
? Accretion stream?
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An accretion into the disk?
Outer galaxy in Red Clump stars

• Heliocentric distance
• TRGB 7.2 0.3 kpc
• 4-10 Gyr population
• s12km/s

(Martin et al 2004, 2005, Bellazzini et al. 2005)
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G. Lewis
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c.f. Andromeda...
Blue RGB
Red RGB
125 kpc
Qualitatively consistent with predictions (e.g.
Abadi et al. 2003)
95 kpc
Outer disk substructure
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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
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New M31 satellites Metal-poor
CFHT/MegaCam (Martin et al. 2006 in prep)
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New M31 satellites Metal-rich
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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)
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existence proof Pal5
Pal5 Odenkirchen et al (2001)
Dehnen, simulation
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GAIA

• 1 billion stars surveyed to V20
• proper motions 10µas at V15
• velocities for 108 stars (2-10km/s) to V17
• 10 accuracy parallaxes to 10kpc
• However, no chemical finger-printing

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Chemical tagging...
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Venn et al. 2004
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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