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

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

Kirby+08 DWARF SPHEROIDAL GALAXIES OBSERVATIONS Ultra faint dSphs: L tot ≤ 10 5 L  Classical dSphs: L tot > 10 5 L  Gas-free galaxies (only exception LeoT) hosted by small dark matter haloes M < 10 9 M . They all contain an old stellar population and they are metal-poor.

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

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 SCL SXT Ultra-Faint vs classical vs stellar halo Courtesy of Kim Venn * * * Venn+12; see also Simon+10

THE MILKY WAY SYSTEM FORMATION

Radiative feedback: minimum mass for SF Chemical feedback: Z  Z cr PopIII stars M = 200 M  Z > Z cr PopII/I stars Larson IMF Mechanical feedback M ej  ε w N sn /v 2 esc MW GALACTIC MEDIUM z = 20 Time z = 0 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 faint SN m * = 25 M  GAlaxyMErgerTree&Evolution Salvadori,Schneider&Ferrara07 GAMETE Kobayashi+11

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.. Dijkstra+04 Kitayama+00 f * H2  f * (T vir /10 4 K) 3 Madau, Ferrara & Rees 01; Ricotti & Gnedin 01 H 2 -cooling haloes ERM LRM Salvadori&Ferrara09/12 dynamics Diemand+05; Moore+06 Early/late reionization histories Gallerani+06 Dissociating LW background Ahn+09 Mass threshold Machacek+01

ULTRA-FAINT DWARFS

Formation epochsDwarf spheroidal galaxies 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 Salvadori & Ferrara 09/12 Ultra faint dSphs Classical dSphs Lookbacktime [Gyr] L/L  −1 −3 −4 [Fe/H] −2 Ultra-faint dwarfs are the living fossils of star-forming H 2 -cooling minihaloes ( Salvadori&Ferrara09;Bovill&Ricotti09;Muñoz+09 ) which assembled at z > 8.5

METALLICITY DISTRIBUTION FUNCTIONS DWARF GALAXIES Helmi+06 Starkenburg+10 Kirby+08 Sculptor Ultra faint Sculptor Ultra faint dSphs Salvadori & Ferrara 09 The broad MDF of ultra-faint dwarfs reflects the inefficient star-formation of H 2 -cooling haloes turning into stars < 3% of the potentially available baryons. F = M * / f c M h Madau+08 0 −1 −3 −4 [Fe/H] −2 L/L  2468 Frebel+10 What is the origin of extremely metal-poor stars in classical dSphs ? Salvadori, Ferrara & Schneider 08 Lower pre-enrichment

STAR-FORMATION HISTORIES DWARF GALAXIES Sculptor CB Hercules UMi ComaBereniceUrsa MinorSculptor Salvadori et al. in prep redshift redshift redshift redshift Lookbacktime [Gyr] Lookbacktime [Gyr] Merging processes become important 10 L/L  −1 −3 −4 [Fe/H] −2 Log SFR [M  yr −1 ] 0 −1 −2 −3 −4 −5

DWARFS-DLAs CONNECTION

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

T vir < 10 4 KT vir > 10 4 K Formation epochs M h < 10 8 M  M h = M  M * < 10 4 M  M * = M  Ψ = (0.1-10)M  yr −1 Ψ = 0 Gas-rich z =2.34 :: N HI ≥ 2 ×10 20 cm − 2 Salvadori&Ferrara12 Cooke+2011b Cooke+2011a Prochaska+2007 DLA candidates log N HI [Fe/H] THE MILKY z = 2.3 DWARFS-DLAs CONNECTION

Formation epochsDLA candidates Failed ultra-faint dwarfs M * = M  Salvadori&Ferrara12 [O/H] [C/O] Star-less minihaloes CHEMICAL ABUNDANCES DWARFS-DLAs CONNECTION Passive evolution Becker+2012 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 ≥ Z cr ≈ 10 −4 Z   or [Fe/H] ≈ −5 The PopIII imprint is hidden by these stellar populations

CONCLUSIONS

Ultra-Faint dwarfs − Ultra-faint dwarfs are fossil relics of H 2 -cooling minihaloes formed at z > 8.5. − Their broader MDF reflects the inefficient cooling by H 2 molecules. − The rare [Fe/H] < –3 stars in classical dSphs formed in progenitor minihaloes formed at very high redshifts. CONCLUSIONS ULTRA-FAINT DWARF GALAXIES 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 > Z cr.

AccretionSelf-enrichment IMPRINT BY FIRST STARS ? FINAL REMARKS Salvadori, Schneider & Ferrara 2007 Z cr = 10 – 4 Z  Z cr = 10 – 6 Z  Z cr = 0 Galactic halo stars: 2nd generation vs all generations m PopIII = 200 M  m PopIII = ( ) M  Does the unusual chemical composition of two Hercules stars reflect the self-enrichment by first stars?

THANKS !