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Ultra-Faint Dwarf Galaxies as a Test of Early Enrichment and Metallicity-Dependent Star Formation

Ultra-Faint Dwarf Galaxies as a Test of Early Enrichment and Metallicity-Dependent Star Formation. Konstantinos Tassis , Nickolay Gnedin , Andrey Kravtsov. M * -Z relation: quite flat for , steepen for lower masses, become less steep for dwarf galaxies

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Ultra-Faint Dwarf Galaxies as a Test of Early Enrichment and Metallicity-Dependent Star Formation

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  1. Ultra-Faint Dwarf Galaxies as a Test of Early Enrichment and Metallicity-Dependent Star Formation KonstantinosTassis, NickolayGnedin, AndreyKravtsov

  2. M* -Z relation: quite flat for , steepen for lower masses, become less steep for dwarf galaxies • The role of metal in H2 related star formation rate star→metal/interstellar dust→H2→star formation Dust catalyses H2 formation and shield the dissociation by UV radiation (Gnedin & Kravtsov 2010)

  3. Stars are needed to produce metal, and metal is needed to form star • Pre-enrichment by population III stars Their work: • Metallicity-mediated star formation and metal enrichment history by simple model • Simulation with H2 based star formation rate

  4. Simple Analytic model • H2 related star formation rate with UV fields(Gnedin & Kravtsov 2010) • Close box approximation

  5. , the metallicity remains just above the primodial value Z0 for a long time, keeping galaxies low-metallicity, low stellar mass. • , Z is growing approximately linearly with time, and the gas metallicity reaches yeff in High stellar mass high Z galaxies

  6. Bi-modality in M*-Z relation • Bi-modal distribution of stars in one galaxy, relative paucity of stars with intermediate metallicities

  7. Simulation work • Simulation volume 25.6h-1, dark matter particle mass • The model includes molecular hydrogen formation, UV field, metallicity related cooling, dust… (Gnedin & Kravtsov 2010, 2011) • Initial condition: metal pre-enrichment by Pop III star, to start H2 formation and star formation in the models

  8. Bi-modality distribution for M-Z relation and stars in a single galaxy Z=3

  9. Discrepancy with the observation: no bi-modality distribution Some explanations: • Star formation rate may correlate weakly with H2, no star formation “threshold” at low gas metallicity • The pre-enrichment is not just , some regions may be already polluted by Pop II star below the resolution of simulation, The results are resolution dependent?

  10. Thank you!

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