Dwarf Spheroidals and Reionization: Is There a Link

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Dwarf Spheroidals and ReionizationIs There a
Link?

• Nick Gnedin

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Co-starring
Massimo Ricotti (UMD)
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Our backyard
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Who Commands Dwarf Galaxies?
Looks familiar?

• Reionization?
• Formation of LG?
• Just a fluke?

Grebel 1998
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Boiling Out?
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Stripping Off?
(Kravtsov, Gnedin O, Klypin 2004)
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Life of a Dwarf Galaxy
True fossil
Polluted fossil
Survivor
Time
z 6 reionization
z 3 Local Group forms
z 0 today
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Observers view
(Grebel 2005)
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Simulations

• dark matter dynamics
• gas dynamics
• star formation
• metal cooling
• exact physics of primeval plasma
• fine print (secondary electrons, Ly-a pumping,
  )
• radiative transfer

the only phenomenology!
Note non-existing things are not included
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Cosmological Parameters 2003
Baryons 4 Dark matter 23 Dark
energy 73
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Resolving All

• Reionized _at_ z9
• Stopped _at_ z8.3

Space
Local Group _at_z0
Simulation
Simulation
Mass
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Fornax twins
Born 2003 CE
Born 13,283,456,789 BCE
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Who Is Who?
Survivors
Virtual dwarfs
Polluted fossils
True fossils
Real dwarfs
Too bright too large to be fossils
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Star Formation
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Metallicity
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Kinematics
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Metallicity Spread I
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Metallicity Spread II
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Dividing the Loot
Survivors
Luminosity
True fossils
Polluted fossils
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Prediction
True fossils (like And I and And II) are
about 1.5 Gyr older than survivors (like WLM or
NGC3109) Horizontal Branch Index can test this!
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Reionizations Iridum Layer HB Index
Mackey Gilmore 2004
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And I vs WLM
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Lilliput Spheroidals?
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Conclusions

• Virtual galaxies formed before reionization
  resemble lowest mass dwarf spheroidals in all
  observable properties is it a coincidence?
• Possible tests

• spatial distribution with the Local Group (need
  to relate z0 and zgt6)
• metallicity spread (but virtual dwarfs have it
  too)
• alpha-to-iron ratio (no signatures of SNIa in
  dSphs Tsujimoto 2005)
• relative ages using the HB index (perhaps, the
  best method)
• existence of lilliput spheroidals.

Sextans
Ursa Major
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The End
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The Brief History of Time
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