dwarf spheroidal galaxies : a landmark for galaxy formation · dwarf spheroidal galaxies : a...
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Dwarf Spheroidal galaxies : a landmark for galaxy formation
Pascale Jablonka
Ecole Polytechnique Fédérale de Lausanne (EPFL)&
Observatoire de Paris
with special thanks to
Yves Revaz and Matthew Nichols
Sculptor Carina
Time Time
Star
For
mat
ion
Rat
e
Rizzi et al. 2004
Out
In
also Tolstoy et al. 2004; Battaglia et al. 2006
a variety of star formation histories
Sculptor Frebel et al. 2010 Tafelmeyer et al. 2010
Hill et al, in prep
Fornax Tafelmeyer et al. 2010 Letarte et al. 2010
UMaII, ComberI: Frebel et al 2009 Draco: Shetrone et al. 2001; Fulbright et al. 2004; Cohen & Huang 2009 Boötes: Norris et al. 2010 Umi: Shetrone et al. 2001 Hercules: Koch et al. 2008 Leo IV: Simon et al. 2010 SegueI: Norris et al. 2010
Sextans: Shetrone et al., 2001
Aoki et al. ,2009 Jablonka et al., in prep. Carina: Koch et al. , 2008
Lesmale et al. , 2011 Venn et al., 2012
translated in different chemical patterns ..
modeling
• Is the environment the driving parameter ? chance encounters produce a variety of properties
• Can we think otherwise ?
★ How much of the variety is intrinsic ★ When and how is interaction required
GEAR (Revaz & Jablonka 2012)
•Fully self-consistent tree-sph code•High spatial resolution•Detailed chemical diagnostics•Evolution over a full Hubble time
How isolated can
a dwarf galaxy be ?
dark matter
23 Mpc3/h3 pure DM simulation5123=134’217’728 particles Resolution 150 pc/h, 4.5 103M⊙
Revaz & Jablonka 2012
Out of 1500 systems with more than 1000 particles, 144 Local-Group dSph-like haloes with masses between 108 and 109 M⊙
Revaz & Jablonka 2012
Z=6.53 3.72 2.46 1.72 1.46 0.25 0.0
• 50% of the haloes have their density profiles already in place at z=6 (in physical coordinates)
• 98% have an NFW profile, which central densities varying by factor ~ 3 only from 108 to109 M⊙
Core profile supported by the observations (Blais-Ouellette et al. 2001; de Blok & Bosma 2002; Swaters et al. 2003; Gentile et al. 2004, 2005; Spekkens et al. 2005; de Blok 2005; de Blok et al. 2008; Spano et al. 2008)
Yes part of the diversity can be intrinsic
M/LV
LV
Fe/H
LV
Fornax
Sculptor
Sextans
Carina
SNeII
SNeIa
tcool
DART
Inputs Outputs
mass density gas stars DM
massvelocity
stars DM
Sequence ofmass
density
SNe
Evidence for
interaction
trun-cation
216
Gravitational interaction with the Milky Way : what
impact on the SFH and chemical evolution of the
dSphs ?
Possible orbits: perigalacticons of ~40-80 kpc and apogalacticons of ~100-250 kpc
Example of a Sextans-like galaxyPerigalacticon = 63 kpcApogalacticon = 150 kpcEvolution in isolation = 2.6 Gyr3 orbits in 14 Gyr
Flattening of the density profiles ..
... helping gas removal by SNe explosions
Isolated Two One Three
[Fe/H]
N
[Fe/H]
[Mg/Fe]
Metallicity distribution and abundance ratios
Isolated Two One Three
[Fe/H]
N
[Fe/H]
[Mg/Fe]
Metallicity distribution and abundance ratios
Isolated Two One Three
[Fe/H]
N
[Fe/H]
[Mg/Fe]
Metallicity distribution and abundance ratios
Isolated Two One Three
[Fe/H]
N
[Fe/H]
[Mg/Fe]
Metallicity distribution and abundance ratios
[Mg/Fe]
Successful orbits
No interaction induced burst
- - : start
.... : perigalacticon
• Diversity can be intrinsic
• No way to stop star formation in isolation
• Gravitational tides can stop the star formation • It does it before removing the gas
• No induced gravitationally induced bursts
• Chemical properties provide new contraints to the orbital paths Sextans, 2 orbits with large perigalacticons (> 65 kpc) Carina, 1 orbit with moderate perigalacticon (~ 50 kpc)