1 / 20

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.

toril
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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 !

More Related