Chemical Signatures from Stars in the Nearby Dwarf Galaxies

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Chemical Signatures from Starsin the Nearby
Dwarf Galaxies
Kim Venn University of Victoria
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DART Dwarf Abundances and Radial velocities Team

• Eline Tolstoy, Vanessa Hill, Mike Irwin,
• Pascale Jablonka, Amina Helmi, Francesca Primas,
• Kim Venn, Matthew Shetrone, Giuseppina
  Battaglia, Bruno Letarte, Andrew
  Cole, Patrick Francois,
• Andreas Kaufer, Thomas Szeifert, Nobuo Arimoto,
• K. Sadakane, Tom Abel

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A View of Merging Dwarf Galaxies
Johnston 2003
Is the outer halo filled with tidal streams from
disrupted dwarf galaxies that remain
coherent in phase space? (Bullock Johnston
2005 Font et al. 2005, etc. also new
results by Juric et al. 2005 from SDSS)
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Another view of merging dwarfs e.g.,
Brook et al. 2005 thick disk formation
Is the thick or thin disk a result of merging
dwarf galaxies? also Abadi et al. 2003,
Steinmetz et al. 2002, Navarro et al. 2004, 2000,
Helmi et al. 2005, Robertson et al.
2005, etc.
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• No stellar population
• in the Galaxy that
• clearly resembles
• stars in dSph galaxies.
• Venn et al. 2004
• Includes kinematically selected,
• 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) building blocks?
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1. LMC has low a/Fe
Pompeia Hill 2006 preliminary
a/Fe
GAL
LMC
Ba/Y
LMC data
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• The Sgr dSph also shows low a/Fe
• and at higher metallicities

Bonifacio et al. 2003 Monaco et al. 2005
GAL
dSph
LMC
Sgr
Ibata et al 1997
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3. dIrrs also show low a/Fe (although dIrr
chemistries from young stars)
dIrr, dSph
dIrrs NGC 6822, WLM, Sextans A, GR 8 Venn et
al. 2001, 2003, 2004 and the MCs.
Hiill et al. 2003, 1995 Luck et al. 1998 Venn
1999
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What kinds of galaxies have been merging?
not simply higher mass survivors e.g., LMC,
Sgr, and dIrrs (though dIrrs and dSphs do
seem to have similar abundance patterns)
Before giving up and relying on building
blocks with no resemblences to survivors How
about looking at more stars per dwarf, and not
this mixture
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Each dwarf seems to be unique CMD SFH, thus
also expect unique chemical evolutions we
really need many stars in each dwarf galaxy.
Venn et al. 2004 Shetrone et al. 2001,2003
Geisler et al. 2005
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Sculptor dwarf spheroidal galaxy
French GTO FLAMES DART large program ? Hill
et al. 2006 (GIR fiber spectra) ? Venn et
al. 2006 (UVES fiber spectra) ? Shetrone et
al 2003 ? Geisler et al 2005 ? Venn et al 2004 ?
Fulbright 2000
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SCL
If Sculptor is similar to a dwarf that merged
into the Galactic halo, then must have been very
early. i.e., before significant SNIa
contributions could work for Scls a/Fe
but what about Ba/Y?
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Sculptor dwarf spheroidal galaxy

HR UVES ? Shetrone ? Geisler ? Venn Med
FLAMES (preliminary!) ? Hill
Ba/Fe shows rise in s-process at low z ? AGB
contributions. Y from GIR spectra uncertain.
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SCL
The a/Fe and Ba/Y ratios in the most-metal
poor stars in Sculptor do resemble the Galactic
halo. all early merging? i.e., before SNIa
yields? do these first generation of stars
in Sculptor resemble those from non-survivors?
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Fornax elemental abundances
FLAMES-GIR spectra show RGBs more metal-rich than
Sculptor, but still show lower a/Fe
ratios. FNX Globular Clusters show Galactic
ratios though! (Letarte et al. 2005)
?

• ? Shetrone 2003
• Letarte 2006
• preliminary!

?
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Carina detailed abundances (preliminary)
Preliminary analysis of UVES fiber spectra of 6
RGBs and MIKE spectra from Magellen of 2 more
RGBs ? compared with the Sculptor results!
(????)
CAR
Flat to -3.0 !?
Well need gt100s of stars if were going to see
the effects of long intervals without SF.
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• Sculptor Fornax
• Different masses, but abundance ratios of
  their most metal-poor stars in agreement with
  the Galactic halo stars.
• Carina ( Draco?)
• Preliminary results suggest low a/Fe
  even in
• the most metal-poor stars, unlike the
  Galaxy.
• Could Sculptor be a fossil from reionization
  epoch?

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• Chemical evolution model for Sculptor
• Fenner, Gibson, Gallino Lugaro
• (2006, astro-ph/0602489)
• Model specifically examines
• Two SFHs
• feedback effects on X/Y
• s- and r-process yields NEW!

Ricotti Gnedin 2005 SF
Dolphin et al. 2005 SF
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• Fenner, Gibson, Gallino Lugaro
• (2006, astro-ph/0602489)
• Their a/Fe ratios
• Preferential losses of SN
• products lowers a/Fe
• (dotted line, no feedback)
• Both SFHs can fit the data
• (dashed line, zlt6 SFH)
• Data (?) from
• Shetrone et al. 2003
• Geisler et al. 2005
• Interesting that a/Fe is degenerate
• between SFH and finessing feedback

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• Fenner, Gibson, Gallino Lugaro
• (2006, astro-ph/0602489)
• Their r- and s-process predictions
• Again, preferential losses of
• SN products lowers ratios
• (dotted line, no feedback)
• But Ba/Fe and Ba/Y show
• the unique nucleosynthetic
• signature of s-process
• AGBs lt 3 M (or gt 600 Myr)
• (dashed line, zlt6 SFH)
• Data (?) from
• Shetrone et al. 2003
• Geisler et al. 2005

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Conclusions

• Each dSph galaxy seems to have had a unique SFH,
  thus chemical
• evolution. Yet, all seem to differ chemically
  from stellar components in the Galaxy.
• Only most metal-poor stars resemble halo (except
  Car? Draco?)
• so maybe all early merging only for stellar
  component and/or
• resemble first generation stars in dwarfs
  (including building blocks).
• SF seems to have continued in Sculptor after
  reionization?
• Simple interpretation of a/Fe suggests not,
  unless finessed by feedback (Fenner et al. 2006
  modelling).
• but Ba/Y requires s-process contributions, which
  cannot be finessed by feedback.
• The AGB stars required have lt 3 M (gt600
  Myr), thus post reionization.

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