Ultra-Faint%20dwarfs:

1
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
2
HOW MANY ULTRA-FAINT DWARFS ?
OBSERVATIONS
Willman05, Zucker06a/b, Belokurov06/07/08
Milky Way satellite galaxies
SDSS coverage
3
DWARF SPHEROIDAL GALAXIES
OBSERVATIONS
Gas-free galaxies (only exception LeoT) hosted by
small dark matter haloes M lt 109M?. They all
contain an old stellar population and they are
metal-poor.
Ultra faint dSphs Ltot 105L?
Classical dSphs Ltot gt 105L?

4
METALLICITY DISTRIBUTION FUNCTIONS
OBSERVATIONS
Classical dSphs Ltot gt 105L?
Ultra faint dSphs Ltot 105L?
DART
Battaglia06 Helmi06 Starkenburg10
SDSS
Kirby08
N 933
N 513
N 130
25
N 202
N 364
lt 5
5
CHEMICAL ABUNDANCES
OBSERVATIONS
Shetrone01/03, Koch08a/b, Aoki09, Cohen09,
Feltzing09, Tolstoy, Hill Tosi 09,
Frebel10a/b, Norris10, Simon10, Tafelmeyer10,
Lemasle12, Venn12
Venn12
see also Simon10
Ultra-Faint vs classical vs stellar halo



Courtesy of Kim Venn
6
THE MILKY WAY SYSTEM FORMATION
7
SEMI-ANALYTICAL MODELS
THE MW FORMATION
Tumlinson06/10 Salvadori07/08Komiya09DeLucia
Helmi08Li09Font11
Accounting for the cosmological context and for
the evolution of single proto-galaxies

• Radiative feedback minimum mass for SF

• Chemical feedback

faint SN m 25 M?
Z ? Zcr PopIII stars M 200 M?
Kobayashi11
Z gt Zcr PopII/I stars Larson IMF

• Mechanical feedback Mej ? ew Nsn /v2esc

8
SATELLITES CANDIDATES
THE MW FORMATION
Haiman97/00 Gnedin00Ciardi00
NishiTashino00 Madau01 Machacek01
Ricotti01/02 Dijkstra04 SusaUmemura04
AhnShapiro07Johnson07WiseAbel08Okamoto08..
SalvadoriFerrara09/12
H2-cooling haloes
dynamics Diemand05 Moore06
Dijkstra04
Kitayama00
Early/late reionization histories
Gallerani06 Dissociating LW background
Ahn09 Mass threshold Machacek01
9
ULTRA-FAINT DWARFS
10
THE IRON-LUMINOSITY RELATION
DWARF GALAXIES
Salvadori Ferrara 09/12 Bovill Ricotti
09/11 Muñoz09 Revaz09 Li10 Tumlinson 10
Sawala10 Okamoto10
Formation epochs
Dwarf spheroidal galaxies
Lookbacktime Gyr
Salvadori Ferrara 09/12
13
12
10
13.2
8
13.4
Ultra faint dSphs
Classical dSphs
Ultra-faint dwarfs are the living fossils of
star-forming H2-cooling minihaloes
(SalvadoriFerrara09BovillRicotti09Muñoz09)
which assembled at z gt 8.5
11
METALLICITY DISTRIBUTION FUNCTIONS DWARF
GALAXIES
Salvadori Ferrara 09
F M / fc Mh
Sculptor
Frebel10
Ultra faint
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 lt 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
Sculptor
UMi
Hercules
CB
10
10
Hercules
ComaBerenice
Ursa Minor
Sculptor
Merging processes become important
13
DWARFS-DLAs CONNECTION
14
VERY METAL-POOR DLAs DWARFS-DLAs
CONNECTION
Galactic halo stars vs Damped Lya Absorption
systems
Abundance pattern consistent with a Z 0 faint SN
of 25M?
Bensby and Feltzing 06
Kobayashi11
Fabbian09
Cooke11b
Cooke11a
Q Whats the origin of very metal-poor DLAs and
their connection with dSphs ?
15
THE MILKY WAY _at_ z 2.3
DWARFS-DLAs CONNECTION
SalvadoriFerrara12
Gas-rich satellites _at_ z 2.34 NHI 2 1020
cm-2
Formation epochs
Tvir lt 104K
Tvir gt 104K
16
CHEMICAL ABUNDANCES DWARFS-DLAs
CONNECTION
SalvadoriFerrara12
Failed ultra-faint dwarfs M 102-4 M?
Formation epochs
DLA candidates
Becker2012
C/O
Passive evolution
O/H
Star-less minihaloes
C-enhanced DLAs are associated to star-forming
minihaloes virialized at z gt 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 gt 8.5. - Their broader MDF reflects the
inefficient cooling by H2 molecules. - The rare
Fe/H lt 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 gt Zcr .
19
IMPRINT BY FIRST STARS ?
FINAL REMARKS
Salvadori, Schneider Ferrara 2007
Accretion
Self-enrichment
Does the unusual chemical composition of two
Hercules stars reflect the self-enrichment by
first stars?
20
THANKS !