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)