New Light on Dark Stars: Red Dwarfs, Low-Mass Stars, Brown Dwarfs
Ultra-Faint dwarfs: The Living Fossils of the First Galaxies
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Transcript of Ultra-Faint dwarfs: The Living Fossils of the First Galaxies
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
HOW MANY ULTRA-FAINT DWARFS ? OBSERVATIONS
SDSS coverage
2003 census data:
Classical dSphs = 11
2009 census data:
Classical dSphs = 11Ultra-faint dSphs = 14
Willman+05, Zucker+06a/b, Belokurov+06/07/08
Milky Way satellite galaxies
Kirby+08Kirby+08
DWARF SPHEROIDAL GALAXIES OBSERVATIONS
Ultra faint dSphs: Ltot ≤ 105L Classical dSphs: Ltot > 105L
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.
Kirby+08
N* = 130
25%
SDSSDART
Classical dSphs: Ltot > 105LUltra faint dSphs: Ltot ≤ 105L
N* = 933
N* = 202N* = 364
N* = 513
Battaglia+06; Helmi+06; Starkenburg+10
< 5%
Simple Star Formation History Complex Star Formation Historye.g. Dolphin+02; de Boer+11; Lemasle+12Okamoto+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
SCLSXT
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 Zcr PopIII stars M = 200 M
Z > Zcr PopII/I stars Larson IMF
Mechanical feedback Mej εw Nsn /v2esc
MW
GALACTIC M
EDIU
M
z = 20
Tim
e
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+04Kitayama+00
f* H2
f* (Tvir /104 K)3
Madau, Ferrara & Rees 01; Ricotti & Gnedin 01
H2-cooling haloes
ERM
LRM
Salvadori&Ferrara09/12
dynamicsDiemand+05; Moore+06
Early/late reionization histories Gallerani+06
Dissociating LW background Ahn+09
Mass threshold Machacek+01
ULTRA-FAINT DWARFS
Formation epochs Dwarf 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]
131210 13.28 13.4
L/L
2 4 6 8
0
−1
−3
−4
[Fe/
H]
−2
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
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 H2-cooling haloes turning into stars < 3% of the potentially available baryons.
F = M* / fc Mh
Madau+08
0
−1
−3
−4[F
e/H
]
−2
L/L
2 4 6 8
Frebel+10
What is the origin of extremely metal-poor stars in classical dSphs ?
Salvadori, Ferrara & Schneider 08Lower pre-enrichment
STAR-FORMATION HISTORIES DWARF GALAXIES
Sculptor
CB
Hercules
Hercules
UMi
ComaBerenice Ursa Minor Sculptor
Salvadori et al. in prep
42 120 6 8 10 14redshift
42 120 6 8 10 14redshift
42 120 6 8 10 14redshift
42 120 6 8 10 14redshift
Lookbacktime [Gyr]
1312 13.28 1312 13.28 131210 13.28 131210 13.28
Lookbacktime [Gyr] Lookbacktime [Gyr] Lookbacktime [Gyr]
Merging processes become important
1010
L/L
2 4 6 8
0
−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 andFeltzing 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 consistentwith a Z =0 faint SN of 25M
Kobayashi+11
Tvir < 104K Tvir > 104K
Formation epochs
Mh < 108 M Mh = 108-11 M
M* < 104 M M* = 106-9.5 M
Ψ = (0.1-10)M yr−1Ψ = 0
Gas-rich satellites @ z =2.34 :: NHI ≥ 2 ×1020 cm−2
Salvadori&Ferrara12
Cooke+2011b
Cooke+2011a
Prochaska+2007
DLA candidates
log
N H
I
[Fe/H]
THE MILKY WAY @ z = 2.3 DWARFS-DLAs CONNECTION
Formation epochs DLA candidates
Failed ultra-faint dwarfs
M* = 102-4 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 ≥ Zcr ≈ 10−4Zor [Fe/H] ≈ −5 The PopIII imprint is hidden by these stellar populations
CONCLUSIONS
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.
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 > Zcr .
Accretion Self-enrichment
IMPRINT BY FIRST STARS ? FINAL REMARKS Salvadori, Schneider & Ferrara 2007
Zcr = 10 – 4 Z Zcr = 10 – 6 Z
Zcr = 0
Galactic halo stars: 2nd generation vs all generations
mPopIII = 200 M mPopIII = 200 M mPopIII = (0.1-100) M
Does the unusual chemical compositionof two Hercules stars reflect the
self-enrichment by first stars?
THANKS !