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Dwarf Spheroidals and Reionization: Is There a Link?

This study investigates the link between dwarf spheroidal galaxies and the epoch of reionization. Dwarf galaxies, essential to understanding the evolution of the Local Group, reveal insights into star formation, metallicity, and their formation epochs. We analyze the characteristics of "true fossils" and "polluted fossils," discussing the role of these galaxies in the cosmic timeline. Our findings suggest that the low-mass dwarf spheroidals formed before reionization share observable properties with those established at later epochs, raising questions about their survival and distribution in the universe.

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Dwarf Spheroidals and Reionization: Is There a Link?

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  1. Dwarf Spheroidals and Reionization:Is There a Link? Nick Gnedin

  2. Co-starring: Massimo Ricotti (UMD)

  3. Our backyard

  4. Who Commands Dwarf Galaxies? Looks familiar? • Reionization? • Formation of LG? • Just a fluke? Grebel 1998

  5. Life of a Dwarf Galaxy “True fossil” “Polluted fossil” “Survivor” z ~ 6 reionization z ~ 3 Local Group forms z = 0 today Time

  6. Observer’s view (Grebel 2005)

  7. 1 chimp 25 pc @z=8 900 M8 Resolving All • Reionized @ z=9 • Stopped @ z=8.3 Space Simulation Simulation Local Group @z=0 Mass

  8. Fornax twins Born: 2003 CE Born: 13,283,456,789 BCE

  9. Who Is Who? Survivors Polluted fossils Virtual dwarfs True fossils Real dwarfs Too bright & too large to be fossils

  10. Star Formation

  11. Metallicity

  12. Kinematics

  13. Metallicity Spread I

  14. Metallicity Spread II

  15. IC 10 IC 1613 IC 5152 LMC M32 NGC 55 NGC 147 NGC 185 NGC 205 NGC 3109 NGC 6822 Sextans A Sextans B SMC WLM Carina DDO 210 GR8 Fornax Leo A Leo I Leo II LGC 3 Pegasus Sagittarius And I And II And III And V And VI Antlia Cetus Draco KKR 25 Phoenix Sculptor Sextans Tucana Ursa Minor Dividing the Loot Survivors Luminosity True fossils Polluted fossils

  16. 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!

  17. Const survival probability Best fit Lilliput Spheroidals?

  18. 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 z=0 and z>6) • 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

  19. The End

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