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Ultra-Faint dwarfs: The Living Fossils of the First Galaxies

Ultra-Faint dwarfs: The Living Fossils of the First Galaxies. Stefania Salvadori NOVA fellow. A. Ferrara (SNS-PISA). R. Schneider (INAF-IT). First Stars IV – From Hayashi to the Future – Kyoto, Japan 23 May 2012.

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Ultra-Faint dwarfs: The Living Fossils of the First Galaxies

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  1. Ultra-Faint dwarfs: The Living Fossils of the First Galaxies Stefania Salvadori NOVA fellow A. Ferrara (SNS-PISA) R. Schneider (INAF-IT) First Stars IV – From Hayashi to the Future – Kyoto, Japan 23 May 2012

  2. HOW MANY ULTRA-FAINT DWARFS ? OBSERVATIONS Willman+05, Zucker+06a/b, Belokurov+06/07/08 Milky Way satellite galaxies 2003 census data: Classical dSphs = 11 SDSS coverage 2009 census data: Classical dSphs = 11 Ultra-faint dSphs = 14

  3. Kirby+08 Kirby+08 DWARF SPHEROIDAL GALAXIES OBSERVATIONS Gas-free galaxies (only exception LeoT) hosted by small dark matter haloes M < 109M. They all contain an old stellar population and they are metal-poor. Ultra faint dSphs: Ltot≤ 105L Classical dSphs: Ltot > 105L

  4. METALLICITY DISTRIBUTION FUNCTIONS OBSERVATIONS Ultra faint dSphs: Ltot≤ 105L Classical dSphs: Ltot > 105L DART Battaglia+06; Helmi+06; Starkenburg+10 SDSS Kirby+08 N* = 513 N* = 933 N* = 130 25% N* = 364 N* = 202 < 5% Simple Star Formation History Complex Star Formation History Okamoto+in prep. Geha+in prep. e.g. Dolphin+02; de Boer+11; Lemasle+12

  5. CHEMICAL ABUNDANCES OBSERVATIONS Shetrone+01/03, Koch+08a/b, Aoki+09, Cohen+09, Feltzing+09, Tolstoy, Hill & Tosi 09, Frebel+10a/b, Norris+10, Simon+10, Tafelmeyer+10, Lemasle+12, Venn+12 Venn+12 ; see also Simon+10 Ultra-Faint vs classical vs stellar halo * * SCL SXT * Courtesy of Kim Venn

  6. THE MILKY WAY SYSTEM FORMATION

  7. SEMI-ANALYTICAL MODELS THE MW FORMATION Tumlinson06/10; Salvadori+07/08;Komiya+09;DeLucia&Helmi08;Li+09;Font+11 Accounting for the cosmological context and for the evolution of single proto-galaxies GAlaxyMErgerTree&Evolution GAMETE Salvadori,Schneider&Ferrara07 z = 20 • Radiative feedback: minimum mass for SF • Chemical feedback: GALACTIC MEDIUM Time faint SN m* = 25 M Z  ZcrPopIII stars M = 200 M Kobayashi+11 MW Z > ZcrPopII/I stars Larson IMF • Mechanical feedback Mej  εw Nsn /v2esc z = 0

  8. SATELLITES CANDIDATES THE MW FORMATION Haiman+97/00; Gnedin00;Ciardi+00; Nishi&Tashino00; Madau+01; Machacek+01; Ricotti+01/02; Dijkstra+04; Susa&Umemura04; Ahn&Shapiro07;Johnson+07;Wise&Abel08;Okamoto+08.. Salvadori&Ferrara09/12 ERM LRM H2-cooling haloes dynamics Diemand+05; Moore+06 f* H2 f* (Tvir /104K)3 Madau, Ferrara & Rees 01; Ricotti & Gnedin 01 Dijkstra+04 Kitayama+00 Early/late reionization histories Gallerani+06 Dissociating LW background Ahn+09 Mass threshold Machacek+01

  9. ULTRA-FAINT DWARFS

  10. THE IRON-LUMINOSITY RELATION DWARF GALAXIES Salvadori & Ferrara 09/12; Bovill & Ricotti 09/11; Muñoz+09; Revaz+09; Li+10; Tumlinson 10; Sawala+10; Okamoto+10 Formation epochs Dwarf spheroidal galaxies Lookbacktime [Gyr] Salvadori & Ferrara 09/12 8 10 12 13 13.2 13.4 0 Ultra faint dSphs −1 [Fe/H] −2 −3 Classical dSphs −4 2 4 6 8 L/L Ultra-faint dwarfs are the living fossils of star-forming H2-cooling minihaloes (Salvadori&Ferrara09;Bovill&Ricotti09;Muñoz+09) which assembled at z > 8.5

  11. METALLICITY DISTRIBUTION FUNCTIONS DWARF GALAXIES Salvadori & Ferrara 09 F = M* / fc Mh Sculptor Ultra faint dSphs Frebel+10 0 Helmi+06 Starkenburg+10 −1 Ultra faint [Fe/H] −2 Madau+08 Sculptor −3 Kirby+08 −4 2 4 6 8 L/L Lower pre-enrichment Salvadori, Ferrara & Schneider 08 The broad MDF of ultra-faint dwarfs reflects the inefficient star-formation of H2-cooling haloes turning into stars < 3% of the potentially available baryons. What is the origin of extremely metal-poor stars in classical dSphs ?

  12. STAR-FORMATION HISTORIES DWARF GALAXIES Salvadori et al. in prep 0 −1 Sculptor UMi Hercules CB [Fe/H] −2 −3 Lookbacktime [Gyr] Lookbacktime [Gyr] Lookbacktime [Gyr] Lookbacktime [Gyr] 8 8 0 0 0 0 8 10 10 8 2 2 2 2 4 4 4 4 12 12 12 12 13 13 13 13 12 12 12 12 10 13.2 13.2 13.2 13.2 10 0 −4 ComaBerenice Hercules Ursa Minor Sculptor −1 2 4 6 8 L/L −2 Merging processes become important Log SFR [M yr−1] −3 −4 −5 14 14 14 14 6 6 6 6 8 8 8 8 10 10 10 10 redshift redshift redshift redshift

  13. DWARFS-DLAs CONNECTION

  14. VERY METAL-POOR DLAs DWARFS-DLAs CONNECTION Galactic halo stars vs Damped Lyα Absorption systems Abundance pattern consistent with a Z =0 faint SN of 25M Bensby and Feltzing 06 Kobayashi+11 Fabbian+09 Cooke+11b Cooke+11a Q: What’s the origin of very metal-poor DLAs and their connection with dSphs ?

  15. THE MILKY WAY @ z = 2.3 DWARFS-DLAs CONNECTION Salvadori&Ferrara12 Gas-rich satellites @ z =2.34 :: NHI ≥ 2 ×1020 cm−2 Formation epochs DLA candidates Tvir < 104K Tvir > 104K Cooke+2011b Cooke+2011a Prochaska+2007 log N HI [Fe/H] Mh < 108 M Mh = 108-11 M M* < 104 M M* = 106-9.5 M Ψ = 0 Ψ = (0.1-10)M yr−1

  16. CHEMICAL ABUNDANCES DWARFS-DLAs CONNECTION Salvadori&Ferrara12 Failed ultra-faint dwarfs M* = 102-4 M Formation epochs DLA candidates Becker+2012 [C/O] Passive evolution [O/H] Star-less minihaloes C-enhanced DLAs are associated to star-forming minihaloes virialized at z > 8 in metal-free and neutral regions of the MW environment PopII stars may start to form as soon as Z ≥ Zcr ≈ 10−4Zor [Fe/H] ≈ −5 The PopIII imprint is hidden by these stellar populations

  17. CONCLUSIONS

  18. CONCLUSIONS ULTRA-FAINT DWARF GALAXIES Ultra-Faint dwarfs − Ultra-faint dwarfs are fossil relics of H2-cooling minihaloes formed at z > 8.5. − Their broader MDF reflects the inefficient cooling by H2 molecules. − The rare [Fe/H] < –3 stars in classical dSphs formed in progenitor minihaloes formed at very high redshifts. Failed Ultra-Faint dwarfs − Very metal-poor DLAs are star-less minihaloes imprinted by SNII. − C-enhanced DLAs are the gas-rich counterpart of Ultra-faint dwarfs. − They host PopIII stars but their chemical imprints are hidden by normal, low-metallicity PopII stars, which start to form as soon as Z > Zcr.

  19. IMPRINT BY FIRST STARS ? FINAL REMARKS Zcr = 10 – 4 Z Zcr = 10 – 6 Z Zcr = 0 Salvadori, Schneider & Ferrara 2007 Galactic halo stars: 2nd generationvsall generations mPopIII = 200 M mPopIII = 200 M mPopIII = (0.1-100) M Accretion Self-enrichment Does the unusual chemical composition of two Hercules stars reflect the self-enrichment by first stars?

  20. THANKS !

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