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1Romain TeyssierStars’07
Cosmic Star Formation History:the role of diffuse accretion
Romain TeyssierCEA Saclay
http://www.projet-horizon.fr
2Romain TeyssierStars’07
Physics:• Cooling by H, He + metals and heating by Haardt & Madau UV background• Multiphase ISM as a polytropic equation of state• Star formation as a sub-grid model• Supernova driven winds• AGN driven winds ?• Star bursts ?
Many problems:• Overcooling• Angular momentum• Missing satellites
Numerical issues:• SPH versus AMR• Resolution in mass• Resolution in space and time
Next generation of galaxy formation models: MHD ?
Cosmological simulations of galaxy formation
M82 M81
3Romain TeyssierStars’07
Select star forming regions with: Form stars at the local rate:
with
• t0= 1-10 Gyr (Kennicutt 1998)
• α = 0.2-0.02 (Krumholz & Tan 2007)
• n0= 0.01-0.1 H/cm3 (Martin & Kennicutt 2001)
Numerical implementation :spawn constant mass « star particles» drawnfrom a Poisson random process
Star formation modeling
Caveat: this phenomenological approach is valid only for kpc scales.Discs are very smooth (polytrope) and poorly resolvedNext generation simulations: molecular cooling up to 104 H/cc, sub-cell
model for starbursts, MHD…
4Romain TeyssierStars’07
« Quiescent » supernovae driven winds galactic wind versus galactic fountain
1010 M 1011 M
1010 M halo(various λ and t*)
Dubois & Teyssier, 2007, in press.Wind formation only for Vcirc < 80km/s:
Wind break-outafter 1 to 3 Gyr.
Wind efficiencybelow 10%
5Romain TeyssierStars’07
10000h-1kpc 2500h-1kpc 630h-1kpc 160h-1kpc
Dark matterdensity
Gastemperature
Gasdensity
Stellardensity
LCDM universeLbox=10 Mpc/hFinal redshift z=3
comoving
RAMSES code5123 particles1/2 billions cells256 processors350 hours
6Romain TeyssierStars’07
Ionizing radiation flux from young stars and quasars heats up baryons before they collapse:Pressure support preventing gas from collapsing into low-mass DM halos: M200<MF (Gnedin 2000)Inefficent atomic cooling: T200< Tmin ≈104 K Star forming halos: M200 > Mmin=max(MF,Mcool)
A minimal mass for star forming halos ?
Diffuse gas accretion (M200<Mmin) onto star forming halos (M200>Mmin) :
Press & Schechter (1974) mass function
7Romain TeyssierStars’07
Accretion
Cooling
Star formation
Winds COLD DISCSIGM
HOTGAS
STARS
4 mass transfer branches :- Diffuse accretion into halos- Cooling into discs- Star formation within discs- Winds from star forming discs
Baryons logistics using the halo model4 baryon phases :
- Diffuse IGM (Lyα forest)- Hot gas in hydrostatic halos- Cold gas in rotating discs- Stars
Halo model for baryons: a simple analyticalmodel based on the Extended Press andSchechter halo statistics and various SAM-likeapproximations (Rasera & Teyssier 2006).
8Romain TeyssierStars’07
(for all halos with Vcirc<200 km/s)
Delay the peak Lower the amplitude
Hierarchical model predictions
Wind efficencyStar formation time scale
(t* ≈ t0/3)
9Romain TeyssierStars’07
RAMSES simulations with box size: 10 h-1MpcAnalytical model with finite resolution effectsRasera & Teyssier (2006)
Analytical model and simulations
10Romain TeyssierStars’07
Observations : IR, UV, Radio (compilation by Elbaz 2005)Isocontours for z=0 and z=3 are orthogonal.« Best fit » for t0=8 Gyr and ηw= 1 (Rasera & Teyssier 2006)We need very strong supernovae driven winds !
Star formation history in the universe
11Romain TeyssierStars’07
Heavens et al 2004: stellar population of 100000 galaxies (SDSS) Earlier SFH for larger galaxies : anti-hierarchical ? Fast decline of SFH for large objects at low z⇒ SF shutdown, bimodal accretion, PdV heating, AGN feedback ?
Star formation shut-down above a critical mass ?
Star formation history in individual halos
12Romain TeyssierStars’07
MareNostrum galaxy formation project
GADGET team: G. Yepes, S. Goettlober, M. Hoeft, A. Khalatyan…RAMSES team: R. Teyssier, D. Aubert, E. Audit, J. Devriendt, C. Pichon…with strong support from BSC and IDRIS.
GADGET RAMSES SPH z=5.7 AMR
50 h-1 Mpc box with 10243 particles and 4 billion AMR cells10243 base grid +5 levels of refinement (smallest cell is 2 kpc physical)N body + gas, cooling, star formation, polytrope, supernovae blast waves, metals
13Romain TeyssierStars’07
Bimodality: cold streams or hot shocks?
Birnboim & Dekel (2003)Kravtsov (2003)Keres et al. (2005)Dekel & Birnboim (2006)
SSDS data (from Baldry et al. 2005)
MareNostrum run
Hypothesis: the galaxy star formation historydepends on the geometry of the diffuse accretion.Filaments feed directly fresh gas into the disc.Hot shocks stop cooling and therefore gas accretion.
Shock stability: tcool(ρvir) ~Rvir/Vvir
Filament survival: tcool(ρf) ~Rvir/Vvir
Density enhancement: ρf Tf ~ρvirTvir
14Romain TeyssierStars’07
Accretion-weighted histograms
60% of accretionin cold phase
40% of accretionin hot phase
20% of accretionin cold phase
80% of accretionin hot phase
Ocvirk, Pichon & Teyssier (2008) in preparation
A proxy for detecting hot shocks: accretion-weighted histogram @ 0.2xRvirA proxy for detecting cold streams: accretion-weighted histogram in [0.2-1]xRvirCritical temperature T0=2.5x105 K (as in Keres et al. 2005)
15Romain TeyssierStars’07
Bimodality in smooth accretion flows
Metallicity of the hot phase is thekey parameter !
Transition masses for cold streams
Transition masses for hot shocks
Hypothesis: star formation in a galaxy is related to theproperties of the diffuse (filamentary) gas accretion