Des Galaxies aux planètes : le milieu interstellaire

Comment la simulation numérique aide à

comprendre la formation des étoiles et des disques protoplanétairesPatrick Hennebelle pour le PCMI

Dahbia Talbi, Jean-Hugues Fillion, Valentine Wakelam, Alexandre Faure, Franck Le Petit

Benoit Commerçon, Marc Joos, Anaelle Maury, Jacques Masson

Edouard Audit, Andréa Ciardi, Sébastien Fromang, Romain Teyssier,

Gilles Chabrier, Philippe André

Qu’est-ce que le PCMI ? Quels sont ses objectifs ?

La formation des étoiles et des planètes

L’émergence de la complexité

Un écran à soustraire

Hot Ionised Gas

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n =10−2cm−3,T =106K

Molecular Gas

€

10 −100 pc

n =103cm−3,T =10K

Dense Cores

€

0.1 pc

n =106cm−3

T =10K

Large scale structures

Interstellar CyclePlanets

Warm Ionised GasWarm Neutral Gas

Cold Neutral Gas

€

100 pc, n =102cm−3,T =102K

€

n =1cm−3

T =104K

STARS

€

n >1022cm−3,300000 km

Heavy ElementsKinetic energy

Radiation Cosmic Rays

Accretion discs

ECOLE EVRY SHATZMAN 2012

ees2012.ens.fr

In the Interstellar Medium:

Radiation ≈ Thermal ≈ Kinetic ≈ Cosmic Rays ≈ Magnetic

≈1 eV cm-3

=> Energy equipartition

=> Strong coupling between several physical processes

=> Difficult to simplify and isolate the problems

=> Slow progress

Bournaud et al. 2010

Simulating whole galaxies Simulating parts of galaxies

de Avillez & Breitschwerdt 2005

Performing global Simulations

Performed with RAMSESPRACE+ERC project

Hot Ionised Gas

€

n =10−2cm−3,T =106K

Molecular Gas

€

10 −100 pc

n =103cm−3,T =10K

Dense Cores

€

0.1 pc

n =106cm−3

T =10K

Large scale structures

Interstellar CyclePlanets

Warm Ionised GasWarm Neutral Gas

Cold Neutral Gas

€

100 pc, n =102cm−3,T =102K

€

n =1cm−3

T =104K

STARS

€

n >1022cm−3,300000 km

Heavy ElementsKinetic energy

Radiation Cosmic Rays

Accretion discs

The 2-phase modelThermal equilibrium curve (Field et al. 69, Wolfire et al. 95)

CNM

WNM

Unstable

Field 65: performs linear stability analysis of the radiatively cooling fluid equations. Obtains the isobaric criteria for instability:

€

∂P∂ρ

⎞

⎠ ⎟L= 0

≤ 0

Wolfire et al. 95

20 p

c

Turbulence within a bistable fluid(Koyama & Inutsuka 02,04, Kritsuk & Norman 02, Gazol et al. 02, Audit & Hennebelle 05, Heitsch et al. 05, 06, Vazquez-Semadeni et al. 06)

-Forcing from the boundary

-Statistical stationarity reached

-complex 2-phase structure

-cnm very fragmented

-turbulence in CNM is maintained by interaction with WNM

25002

Audit & Hennebelle 05

3D simulations12003

Intermediate behaviourbetween 2-phase and polytropic flow

50 pc

Formation of a molecular cloud :

-with Cooling -Isothermal

Converging flow

Importance of CoolingFor the Formation of Structures

Gas-phase chemical modeling

Model parameters : -Temperature (K)-Density (cm-3)-Elemental abundances-UV, X-rays, cosmic-rays fields-Chemical networks

Computation of the chemical abundances :

dni/dt = klj nlnj - ni kij nj

Production Destruction

k : reaction rate coefficients

A large community of French chemists and physicists, theoreticians and experimentalists are involved in the determination of accurate k (Bordeaux, Dijon, Montpellier, Paris, Rennes)

A + B → C + D

KIDAKinetic database for Astrochemistry

H=EQCT, RRKM, TST …….

k (T)

CRESU

Astrochemical modelling

Kinetic Data Base (KIDA)

Measurment at low T and P

Hot Ionised Gas

€

n =10−2cm−3,T =106K

Molecular Gas

€

10 −100 pc

n =103cm−3,T =10K

Dense Cores

€

0.1 pc

n =106cm−3

T =10K

Large scale structures

Interstellar CyclePlanets

Warm Ionised GasWarm Neutral Gas

Cold Neutral Gas

€

100 pc, n =102cm−3,T =102K

€

n =1cm−3

T =104K

STARS

€

n >1022cm−3,300000 km

Heavy ElementsKinetic energy

Radiation Cosmic Rays

Accretion discs

Flow of WNM (density 1cc), velocity 20km/s each side, initial magnetic field 5G, gravity included

Internal clump velocity dispersion(density > 2500 cm-3)

€

σ(L) ≈1 kms−1 L /1pc( )0.5

Klessen & Hennebelle (2010)

σR0.5

Falgarone 2000

Compatible with Larson law=>is turbulence within GMC driven from outside ?

Iffrig & Hennebelle in prep 2012

Influence of supernovae explosions within molecular clouds

Hot Ionised Gas

€

n =10−2cm−3,T =106K

Molecular Gas

€

10 −100 pc

n =103cm−3,T =10K

Dense Cores

€

0.1 pc

n =106cm−3

T =10K

Large scale structures

Interstellar CyclePlanets

Warm Ionised GasWarm Neutral Gas

Cold Neutral Gas

€

100 pc, n =102cm−3,T =102K

€

n =1cm−3

T =104K

STARS

€

n >1022cm−3,300000 km

Heavy ElementsKinetic energy

Radiation Cosmic Rays

Accretion discs

The core mass function(Motte et al. 1998, Testi & Sargent 1998, Alves et al. 2007, Johnstone et al. 2002, Enoch et al. 2008, Simpson et al. 2008)

Alves et al. 2007 Konyves, André et al. 2010

Extending Press-Schecter (1974) approach to the supersonic turbulent case

Principles of Press-Schecter analysis

Used in cosmology to predict the mass spectrum of DM haloes: =>very successful

-consider a spectrum of density fluctuations (Gaussian in the cosmological case) characterized by its powerspectrum and smooth it at scale R

-setup a criterion to decide which perturbations have to be considered (collapse time should be smaller than the age of the universe)

-sum over the corresponding fluctuations

In the case of Molecular clouds

(Padoan et al. 1997, Hennebelle & Chabrier 2008, 2009, 2011, Hopkins 2011, 2012)

-assume that the density PDF is log-normal

-the power-spectrum of log is close to Kolmogorov

-consider a uniform density threshold

-consider self-gravitating structures

Comparisons with numerical simulations

No free parameter

Hennebelle & Chabrier 2009Comparison with numerical simulations from Jappsen et al. 2005 with gravity

Schmidt et al. 2010Comparison with high resolution numerical simulations without gravity

Hot Ionised Gas

€

n =10−2cm−3,T =106K

Molecular Gas

€

10 −100 pc

n =103cm−3,T =10K

Dense Cores

€

0.1 pc

n =106cm−3

T =10K

Large scale structures

Interstellar CyclePlanets

Warm Ionised GasWarm Neutral Gas

Cold Neutral Gas

€

100 pc, n =102cm−3,T =102K

€

n =1cm−3

T =104K

STARS

€

n >1022cm−3,300000 km

Heavy ElementsKinetic energy

Radiation Cosmic Rays

Accretion discs

XYhydro

XZhydro

XYMHD=2

XZMHD=2

300 AU

A collapse calculation (zoom onto the central part)(Hennebelle & Fromang 2008, Commerçon et al. 2010, Joos et al. 2012)1 solar mass slowly rotating core

B,

B,

Comparison of the PdBI maps with MHD simulations

Hydrodynamical simulations produce too much extended (+ multiple) structures if compared to the observations.

MHD simulations ?

Taurus PerseusHennebelle & Fromang (2008)Hennebelle & Teyssier (2008) MHD simulations : produce PdB-A synthetic images with typical FWHM ~ 0.2’’ - 0.6’’

Similar to Class 0 PdB-A sources observed !

need B to produce compact, single PdB-A sources.

White dashed : 3sigma level. Thick black : 5sigma level

Maury et al. 2010

Hincelin U., Commerçon B., Wakelam V., Hersant F., Guilloteau S., Aikawa Y. en préparation

Chimie 3D de l’effondrement des cœurs denses - formation des disques protoplanétaires

Chimie gaz-grain NAUTILUSHersant et al. 2009Hincelin et al. 2011

CO(gaz)/H

x(UA)

z(UA)

y(UA)

Effondrement 3D (RMHD)RAMSES

Teyssier 2002Fromang et al.

2006Commerçon et al.

2011T(K)

30

100

300

x(UA)0 50-50 100-100

0

50

-50

100

-100

y(UA)

0

50

-50

100

-100

y(UA)

log n(cm-3)

13

12

11

10

t=4.104ans

Chimie 3D

5PhotodesorptionPhotodesorption UVUV d’un analogue de glace interstellaire :

Première étude expérimentale de la dépendence en longueur d’onde.

δ 5 10-2 molecule/photon

CO

Au, 18 K

Direct excitation of CO

CO desorptionUV photon (170-90 nm)

Fayolle et al. APJ 2011

Photodésorption de CO (15 K)

Expérience Ultra-vide & utilisation du rayonnement synchrotron (SOLEIL)

Compréhension du mécanisme microphysique Taux de photodésorption dans

différents champs de rayonnement

•PDR Data Base (LUTH / MIS) Modèles de nuages interstellaires pour Herschel, IRAM, ALMA, VLT, HST, FUSE, ...• Interprétation «ordre 0» ou préparation d’observations

• densité de colonne de centaines d’espèces chimiques• intensités de raies, spectres• structures des nuages

Bases de données théoriques pour le MIS

Starformat (LERMA / ENS)• Simulations MHD du gaz interstellaire

• Formation des nuages, coeurs denses, ...

• Propriétés de la turbulence• Propriétés des coeurs denses

• distribution masse, vitesse, ...

• Post-traitement fournissent observables

• Développement international

• Application : milieu diffus, régions de formation d’étoiles, milieu intergalactique, ...

Conclusions

La formation des étoiles et des planètes sont des processus intimement liés qui sont :

-multi-échelles-multi-physiques

impliquant la synergie entre :

-observations-théories non-linéaires-simulations numériques-développement et maintien de codes-expériences de laboratoire-bases de données

Des progrès importants ont été réalisés (IMF, SFR, fragmentation). ALMA ouvre de grandes perspectives.

Column density

Density cut Temperature

Magnetic field

Although the cloud appears as a single phase entity in projection, its structure is not very different from the CNM/WNM structure. Clumps are bounded by WNM which provides them a confining pressure.