Dwarf Spheroidal Galaxies : From observations to models and vice versa Yves Revaz
The good reasons to study dSphs : Test for the LCDM paradigm : small structures are predicted in abundance Galaxy luminosity function Bower et al. 2003
The good reasons to study dSphs : The missing satellite problem LCDM simulations predict the existence of a high number of dwarf galaxies orbiting around Andromeda and the MilkyWay... ...but only a modest population is observed. Via Lactea (Diemand et al. 2007) Simon & Geha 2007
The good reasons to study dSphs : In the hierarchical LCDM paradigm, dSphs are the building blocks of larger objects Dwarf galaxies Spiral galaxies time Elliptical galaxies Galaxy clusters
The good reasons to study dSphs : Much more complex than usually thought Tinguely 1970
Agenda What is a dSph galaxy ? How do we model these objects ? ➢ The driving parameters ➢ Intrinsic or extrinsic evolution ? Can we predict the stellar mass for a given halo mass Some conclusions
What is a dSph galaxy ? Faint stellar system (Mv < -15) Low velocity dispersion (~10 km/s) Evidence for dark matter No clear rotation (dominated by random motions) No ongoing star formation No gas (or at least not detected) [Fe/H] follows luminosity
clustered around spiral galaxies dSphs are interior to transition systems, themselves interior to dIrrs Mateo 2008
diffuse objects core core tidal tidal Fornax Carina Piatek, 2007; 2003
they form a sequence Adapted from Tolstoy, Hill & Tosi 2009
...but are also very different Sculptor Carina Vt=198 ±50 km/s Vt=85 ±39 km/s Vr=79 ±6 km/s Vr=22 ±24 km/s Peri : 68 kpc (33, 83) Peri : 20 kpc (3, 63) Apo :122 kpc (97,133) Apo :102 kpc (102,113) Period : 2.2 Gyr Period : 1.4 Gyr today today Piatek et al. 2006, 2003
disparate, structures, diff. stellar pop as fct of r Sculptor Carina Star Formation Rate Out In Time Time Rizzi et al. 2004 also Tolstoy et al. 2004; Battaglia et al. 2006
What is at the origin of the diversity ? ● 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 ? ➢ Sequence = single framework of formation ?
Current limitations ➢ Too simplistic chemical evolution ➢ Arbitrary fixed SFH ➢ Small number of simulations ➢ Evolution stopped at high z ➢ Confront results only with global relations
Global relations are not all... Objects with very similar : - Lv - [Fe/H] - [M/Lv] ...
... may have completely different stellar and chemical properties ! SFR, M * AGE [Fe/H] [Mg/Fe]
Observations : Where do we stand ? ● Accurate abundances measurement from individual stars for: ➢ Fornax (Letarte et al. 2010) ➢ Sculptor (Hill et al. in prep.) ➢ 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., in prep.) DART Team DART Team
Modelisation Code & physical processes The initial conditions Tests and Robustness
GEAR : a self-consistent Tree/SPH code (Revaz & Jablonka 2012) Skeleton : Gadget-2 (Springel 2005) Gravity : -> treecode (Barnes & Hut 86) NlogN instead of N 2 Hydrodynamics : -> SPH : Smooth Particles Hydrodynamics (Lucy 77, Gingold & Monaghan 77) Hydrodynamics values are obtained by convolution of neighbors particles with a kernel function the resolution follows the mass
GEAR : a self-consistent Tree/SPH code The baryon physics Cooling function (metal dependent) : - above 10 4 K (Sutherland & Dopita 93) - below 10 4 K, H 2 , HD, OI, CII, SiII, FeII (Maio et al. 07) Star formation : classical recipes : Schmidt law (Schmidt 59) (Katz 92) + star formation density (0.1 a/cm 3 ) + starformation temperature (3x10 4 K)
GEAR : a self-consistent Tree/SPH code Chemical evolution SSP scheme : (Poirier 03, PhD thesis) - SNIa, SNII nucleosynthesis + feedback from SN explosions - elements followed : Fe, Mg
Time Kodama & Arimoto 97 Formation time of a stellar particle (SSP) mass fraction IMF : Krupa 01 yields energy Injection into the system : nearest neighbors
SNII : yields of massive stars (Iwamoto et al. 99) Energy : e SN 10 51 ergs/SN (thermal)
SNIa : model from Kobayashi et al. 2000 yields from Tsujimoto et al. 95, updated models Energy : e SN 10 51 ergs/SN (thermal)
Outputs of models and observables stellar particles : ➢ Fe, Mg, Z, age -> Lv (Vasdekis et al. 96) gas particles : ➢ Fe, Mg, Z, density, temperature all particles : ➢ positions, velocities, mass
Initial conditions
Initial conditions - 2 Mpc/h 3 box, dark matter only (WMAP V) more than 150 dSph haloes with - 134'217'728 particles masses between 10 8 > M > 10 9 M sol => resolution of 150 pc/h, 4.5 10 4 M sol /h
Z=6.53 3.72 2.46 1.72 1.46 0.25 0.0
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 coordinate) 98% have an NFW profile, wich central densities varying by a fractor ~3 only (for masses between 10 8 and 10 9 M sol )
Initial conditions : isolated models Models of dSphs in a static Euclidean space, where the expansion of the universe is neglected, ● are justified. The physics of baryons that depends on the density in physical coordinates is correct. The densities of haloes with mass between 10 8 and 10 9 Msol exhibit a small dispersion, a factor ● 3 to 4, which could help understanding the variety in the observed properties of the dSphs 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)
Energy conservation, Robustness & Convergence tests
9.5x10 8 Msol Conservation better than 5% over more than 250 dynamical times !
chemical properties : - metallicity distribution - abundances density profile
Results
Parameters (see also Revaz et al. 2009) More than 400 simulations, Exploring the effect of the parameters
Efficiency of supernova energy : Mass = 4x10 8 M sol e SN = 100% e SN = 1% ➢ If e SN =100% (10 51 ergs per SN) → no Fe/H enhancement (need to be below 10%) ➢ no strong winds : the gas is kept around the system ➢ 10 7 M sol of gas linked to the dSph (see also Marcolini et al. 06, Valcke et al. 08)
Mass or density ? density x 5 : Δ[Fe/H]= 1.0 dex c * =0.05 e SN =0.03 mass x 9 : Δ[Fe/H]= 0.5 dex density • Cooling stronger for larger densities • Mass increases luminosity but has • negligible impact on the chemical • evolution mass
Fornax 7x10 8 M sol Sculptor 5x10 8 M sol Sextans 3x10 8 M sol Carina 1x10 8 M sol
Do we observe a sequence ? Yes The dominant driving parameters are the mass and density ● (compatible with the cosmology) More massive and dense systems, forms stars continuously ● ➢ → high [Fe/H] → high Lv Less massive and less dense sytems forms stars episodically ● ➢ → low [Fe/H] → low Lv But we need outer physical processes to truncate the star formation ➢ to get rid of the remaining gas ➢
Metallicity gradients Sextans (Battaglia et al. 2011) Fornax (Battaglia et al 2006) Sculptor (Tolstoy et al. 2004)
Metallicity gradients metalicity gradients ?
Metallicity gradients : the effect of gas motion High resolution model : M=3.5 10 8 M sol , 4x10 6 of particles ➢ hot gas heated by SNs accumulates at the center ➢ due to strong Archimedes forces this gas is driven outside ➢ high metallic gas is ejected into the IGM (1.5 10 5 M sol )
Metallicity gradients : the effect of gas motion High resolution model : M=9.5 10 8 M sol , 4x10 6 of particles
How galaxies populates their dark matter halo ?
Abundance matching • Millennium Simulation (MS; Springel et al. 2005) • High resolution MS (Boylan-Kolchin et al. 2009) • SDSS/DR7 Assume • main subhaloes and satellite subhaloes have galaxies at their centres, Guo et al. 2010 • the stellar masses of these galaxies are directly related to the maximum dark matter mass ever attained by the subhalo during its evolution. In practice, this mass is usually the mass at z= 0. • one-to-one and monotonic relationship between M halo and M * n(>M halo ) = n(>M * )
Abundance matching : Sawala et al 2011 SDSS+Millenium Guo et al 2010 Extrapolation Sawala et al 2011
Abundance matching Sawala et al 2011 SDSS+Millenium Guo et al 2010 Who is right ? Who is wrong ?
Faber-Jackson / Tully-Fisher relation SDSS+Millenium Guo et al 2010
Faber-Jackson / Tully-Fisher relation SDSS+Millenium Guo et al 2010
Faber-Jackson / Tully-Fisher relation SDSS+Millenium Guo et al 2010
Can we find 10 km/s stellar systems in 10 10 M sol halos ?
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