Dwarf galaxies Galactic Halo relations

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Dwarf galaxies - Galactic Halo relations
V. Hill, GEPI, l'Observatoire de Paris
The DART-eam E. Tolstoy, B. Letarte, G.
Battaglia, A. Helmi (Kapteyn institute), M. Irwin
(IoA), K. Venn (Victoria), M. Shetrone (Mc Donald
Observatory), P. Jablonka (Genève), P. Francois
(GEPI, Obs Paris), F. Primas, A. Kaufer, T.
Szeifert (ESO), N. Arimoto, S. Sadakane (Japan)
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Merging debris

• Is the outer halo filled with tidal streams from
  disrupted dwarf galaxies that remain coherent in
  phase space?
• (Bullock et al. 2002, Font et al. 2001, 2005,
  Johnston et al. 2002, etc.)
• Are the thick or thin disk the result of merging
  dwarf galaxies?
• (Abadi et al. 2003, Steinmetz et al. 2002,
  Navarro et al. 2004, 2000, Brooks et al. 2005,
  Helmi et al. 2005, etc.)

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Chemical signatures ?
Venn et al. 2004
No stellar population in the Galaxy ? stars in
dSph galaxies.

• halo
• retrograde stars
• thick disk
• thin disk

What kinds of galaxies have been merging?
higher masses? (e.g., Brook et al. 2005 etc.
Robertson et al. 2005) Or did it ALL
happen very early? before significant star
formation in the dwarfs? (e.g., Font et al
2004, etc.) Or ?
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• DART
• Dwarf Galaxy Abundances and Radial Velocities
  Team
• Sculptor, Fornax, Sextans, (Carina)
• FLAMES Programs ( FLAMES GTO Observatoire de
  Paris)
• HR abundances in central regions for detailed
  abundance analysis
• LR abundances over the whole galaxy for a wider
  view of metallicities and kinematics of the
  entire system using only CaT.
• WFI imaging, over entire area of galaxies,
  looking for any sign of large scale spatial
  variations in stellar populations, and to provide
  spectroscopic targets.
• Sculptor Tolstoy et al. 2004 (LR) and Hill et
  al. 2007 in prep
• Fornax Battaglia et al. 2006 (LR) and Letarte
  PhD thesis 2007

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Sculpteur
Fornax
Bersier 2000 field40'x40'
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LR spectroscopy (CaT)
WFI/FLAMES Sculptor dSph
Battaglia et al. 2006
Tolstoy et al. 2004
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Sculptor (308 confirmed members)
Tolstoy et al. 2004 ApJL
Tolstoy et al. 2004
Metallicity distribution variation...
Associated with different kinematics
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Fornax
Battaglia et al. 2006
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Two-populations

• What do two populations mean?
• Star formation history
• initial burst, blowout returned enriched
  to center
• Chemical evolution
• may expect different chemical properties for
  each population (?)
• Consequences
• Comparison with the Galaxy
• what subpopulation have we compared to the halo
  so far?
• Mass determination
• may help alleviating the degeneracy with
  anisotropy (Battaglia thesis 2007, and paper
  subm.)

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HR abundances Hill et al. 2007 in prep.
HR abundances Letarte PhD thesis 2007
Sculpteur
Fornax
(V-I)
(V-I)
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High resolution abundances
HR
HR
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Distinct evolution
LMC Fornax Sculptor

• ?-elements
• Different evolutionary tracks !
• sequence following SFH-timescales (or Luminosity)
• Metal-poor stars agree everywhere

LMC Pompeia, Hill et al. 2007 in press Fornax
Letarte PhD thesis 2007 Sculptor Hill et al. 2008
in prep
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N-captures
LMC Fornax Sculptor

• s-process (low-intermediate mass AGBs- Y,Ba
• Ba/Fe distinct paths.
• AGB lifetimes s-process yields are Z-dependent
  (seeds)
• s- process very efficient in galaxies with
  strong SFR at younger ages (lt5Gyrs) Fnx gt LMC gt
  Scl
• Eu r-process, massive stars (SNII)
• Eu/Fe similar to ???

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s-/r- fractions
LMC Fornax Sculptor

• Y,Ba s-process, low-intermediate mass AGBs
• s-process takes over very strongly in FnxLMC at
  Fe/Hgt-1.0
• Eu r-process, massive stars (SNII)
• Eu/Fe similar to ????????hard to tell because s-
  overtakes r- at metallicities where SNIa
  contribute
• No difference at the lowest metallicities.

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S-process

• Metal-poor AGBs contribute heavier s-process
  elements (favour 2nd and 3rd peak over 1st peak)
• Fornax (and LMC) AGBs were more metal-poor

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Ubiquitous low-Z component

• Various SFH and therefore MDFs, but same low-Z
  tail

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dSph lack the lowest-Z tail ?

• Beers Christlieb 2006

6-8 stars Fe/Hlt-2.5 per galaxy ? expect 2-3
stars Fe/Hlt-3.0
Helmi et al. 2006
Salvadori Ferrara 2006

• Milky-Way -4 desert
• 2 Fe/Hlt-5 stars with very high CNO

Dwarf spheroidals -3 desert
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CaT versus HR metallicities

• rms0.15-0.2dex
• no systematics except -0.2 at the
  high-metallicity end (above Fe/H-1) ?

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• Conclusions prospects
• Large samples of stars in Sculptor and Fornax
  show
• Two distinct old stellar populations, chemically
  and kinematically. Is this a general property ?
  (hard to tell in galaxies which never reached
  metallicities gt-2 or so)
• Metal poor stars abundances are not significantly
  different from those of the metal-poor halo
• Is this always the case (cf Carina) ?
• Is this the case at the very lowest metallicities
  ? Follow-up of all stars with Fe/Hlt-2.7 in
  progress
• dSph seem to lack the most metal-poor stars found
  in the MW halo (lt-3).
• Check with larger statistics
• Check CaT sensitivities at the lowest
  metallicities
• Chemical evolution consistent with SN Ia
  contributions at lower Fe than in halo
• Very high s-process element content of Fornax and
  the LMC (but NOT in Sculptor), traced to a strong
  pollution by metal-poor AGBs.

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Modelling efforts

• Lanfranchini Matteucci 2005 pure chemical
  evolution model (no dynamics, no energetics)
• Fenner et al. 2006 chemical evolution model with
  energetics of feedback well treated
• Marcolini et al. 2007 3D hydro code with basic
  chemistry
• Jablonka et al. (in prep.) Tree-SPH with basic
  chemistry
• Ripamonti et al. (in prep astroph 2007) GADGET

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Fenner et al. 2006
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3D Hydro code(Marcolini et al. 2007)
ISM
Draco
SNII
SNIa
ISM
SNII
SNIa