A Report of IAU Symposium 270 “Computatioal Star Formation” M. Yamada 1
Introduction/Contents ✦ Program of the symposium: a wide variety in scales, observations 1) individual star formation (low-/high-mass), clusters 2) feedback, triggered star formation 3) star formation over Galactic/extragalactic/cosmological scales 4) ... and so on (incl. numerical techniques and hardwares) ✦ Highlights (personally biased) 1) CMF/IMF and turbulent fragmentation 2) radiative feedbacks (high-/low-mass) 3) synthetic observations 4) turbulent ISM on (Extra-)Galactic Scales 5) misc. ✦ Keywords radiation - radiative (magneto)-hydrodynamics, synthetic observation ✦ fragmentation - too many fragments? mechanisms? ✦ statistics - can it derive correct information? ✦ 2
I.CFM/IFM & Turbulent Fragmentation 3
CMF & IMF I: Observation CMF/IMF in Pipe Nebula (Alves et al.2007) ✦ Observation of Pipe Nebula ✦ mass function of dense core dense core seems to be identical to IMF mass function with a shift in mass ⇒ “ uniform” star formation efficiency (M * /M core ) indep. of core mass? ✦ theorists‘ job become now: IMF ✦ reproduce functional form for the mass function of synthetic “cores” [mostly in large scale simulation, e.g., whole molecular cloud or greater] - why are CMF and IMF look alike? ✦ search for mechanisms to determine the uniform star formation efficiency (=M * /M core ) [mostly in individual cores studies] 4
CMF & IMF I: Observation (2) ✦ Observation of mass function of dense core: ✦ studies of different kinds of cores (starless, prestellar, etc.) ✦ updates in obs./data-analysis techniques ✦ submm. dust thermal emission (850 μ m) gives a better identification of true starless prestellar cores compared with A V measurement in optical (Andre’s talk) ✦ A v cores seem to be gravitationally unbound, while dust emission cores seem to be bound [true prestellar?] ( → Pavlyuchenkov’s talk?) ✦ deep imaging of Pipe Nebula by Herschel (Alves’ talk) ✦ A V (or N H ) PDF <-> log-normal distribution down to low A V regime, consistent with Wada’s simlation ✦ more than 90% of the mass is in low A V ( Σ =46M sun /pc 2 ) ✦ Observational studies of IMF ✦ many samples - cluster IMF seems largely the Salpeter-Scalo type (Ascenso’ talk) ✦ indep. of metallicity, stellar density, environments... ⇒ IMF may not provide a good constraints to models? ✦ numbers of dense clusters can have very massive star (M*>150M sun ) if universal IMF is assumed, but no such massive star has been discovered ⇒ stars determine 5 their mass locally?
CMF & IMF II: Theory (1) CMF/IMF in Pipe Nebula (Alves et Synthesized “IMF” in 3D ISM simulation (Padoan & Nordlund 2002) dense core mass function IMF ✦ “Turbulent fragmentation”: ✦ sheet-like gas which is compressed by shock waves induced by supersonic turbulent flows ( λ frag ~ λ sheet ~L*( ρ 1 / ρ 0 )~L/ M A ) ✦ results are dependent on Mach numbers, but it succeeded in reproduce observed IMF (fragment mass function+ M * =M frag *f J; [f J is defined as a fraction of gravitationally unstable core mass fraction having ρ ∝ r -2 ]) 6 ✦ Different from classical view: magnetically subcritical/supercritical
CMF & IMF II: Theory (2) synthesized density structure (MHD, A V map of Pipe Nebula (Alves et al. 2007) Padoan et al. 2006) Simulation looks really like to real clouds, but..? 7
CMF & IMF II: Theory (2) synthesized density structure (MHD, A V map of Pipe Nebula (Alves et al. 2007) Padoan et al. 2006) Simulation looks really like to real clouds, but..? ✦ “Turbulent fragmentation”: criticism and problems ✦ mostly isothermal simulation <-> multi-phase ISM in real universe ✦ origin of supersonic turbulence? -> avoids by adding turbulent fields by hand ✦ boundary conditions? <-> no apparent periodicity in real ISM ✦ larger scale simulation so as to set a more realistic boundary? (how?) ✦ what kind of quantities are to be compared with observations? 7
CMF & IMF II: Theory (3) - analysis - Power spectrum (Padoan et al. 2006) 1-st order velocity structure function (Kritsuk et al. 2007) ✦ ISM turbulence simulation anlaysis: criticism and problems ✦ power spectrum? -> P(k) ∝ k -a , a=5/3 (Kolmogorov), a=2(Burgers) ✦ random phase assumption? <-> anisotropic flow (e.g., by magnetic filed) ✦ structure function? S p (l) = <| u(r+l)-u(r) | p > ✦ Statistical analysis sometimes erases important information.. ✦ different models can give the (almost) same power spectrum 8
CMF & IMF III: Theory (4) multi-phase ISM Kritsuk’s talk & Ostriker’s talk 2D MHD sim. of SNR (Inoue et al. 2009) ✦ Thermal instability makes multi-phase ISM w/ turbulent velocity ✦ tiny cold clumps embedded in warm diffuse phase ✦ (basically) solves the dissipation problem ✦ efficient enough? relation to the star formation? ✦ Time-dependent pressure can work as regulation of SFE? (Ostriker’s talk) ✦ SFE up → P ex increases to thermally stable ISM → rapid SF → termination of stellar 9 feedback lowers P ex to thermally unstable phase → cold phase form stars
CMF & IMF III: Theory (5) theory of IMF Hennebelle’s talk ✦ Analytic modeling of IMF w/ Press-Schechter formalism ✦ PDF of over-dense regions: log-normal in non-gravitational turbulent ISM <-> Gaussian in cosmology ✦ assume “star formation” when average density exceeds a threshold (e.g., CO gas) → analytic formula for mass function δ c: free parameter to specify physical process of SF ✦ it has the same shortcomings as PS, but it succeeded in describing synthetic IMF taken from simulation ✦ convenient for examining what process is essential for determining IMF 3 10 Hennebelle & Chabrier (2008)
II. Radiative Feedbacks & Individual SF 11
Low-mass SF I: Observation Evans’ talk ✦ Spitzer c2d project: ✦ age estimates of Class I/0 is longer than previous ones (0.54Myr/0.35Myr) ✦ but it does not solve the “luminosity problem” (L obs <<L acc (theory)~10 -6 M sun /yr) ✦ intermittent accretion?/competitive accretion? ( → McKee’s talk) ✦ Review of disks of YSO (Duchene’s talk) ✦ existence of disk and basic properties are almost independent of the mass of protostar (0.5M sun <M*<5M sun ) or of feedbacks from nearby massive stars ✦ disk mass of class 0 seems to be larger than that of class 1 → opposite sense to the classical picture? ✦ Spitzer 8 μ m obs. of envelopes of Class 0 objects (Tobin’s talk) ✦ found significantly irregular morphology @1,000 AU ✦ velocity sub-structure inside a core : dynamics of the very early phase ✦ origin? → 12
Low-mass SF I: Observation Evans’ talk ✦ Spitzer c2d project: ✦ age estimates of Class I/0 is longer than previous ones (0.54Myr/0.35Myr) ✦ but it does not solve the “luminosity problem” (L obs <<L acc (theory)~10 -6 M sun /yr) ✦ intermittent accretion?/competitive accretion? ( → McKee’s talk) ✦ Review of disks of YSO (Duchene’s talk) ✦ existence of disk and basic properties are almost independent of the mass of protostar (0.5M sun <M*<5M sun ) or of feedbacks from nearby massive stars ✦ disk mass of class 0 seems to be larger than that of class 1 → opposite sense to the classical picture? ✦ Spitzer 8 μ m obs. of envelopes of Class 0 objects (Tobin’s talk) ✦ found significantly irregular morphology @1,000 AU ✦ velocity sub-structure inside a core : dynamics of the very early phase ✦ origin? → 1) dynamically unstable initial condition? 2) mis-alignment of (global) B-field and rotation axis? 12
Low-mass SF I: Observation ↓ contour: τ Evans’ talk ✦ Spitzer c2d project: ✦ age estimates of Class I/0 is longer than previous ones (0.54Myr/0.35Myr) ✦ but it does not solve the “luminosity problem” (L obs <<L acc (theory)~10 -6 M sun /yr) ✦ intermittent accretion?/competitive accretion? ( → McKee’s talk) ✦ Review of disks of YSO (Duchene’s talk) ✦ existence of disk and basic properties are almost independent of the mass of protostar (0.5M sun <M*<5M sun ) or of feedbacks from nearby massive stars ↓ contour: SCUBA ✦ disk mass of class 0 seems to be larger than that of class 1 850µm → opposite sense to the classical picture? ✦ Spitzer 8 μ m obs. of envelopes of Class 0 objects (Tobin’s talk) ✦ found significantly irregular morphology @1,000 AU ✦ velocity sub-structure inside a core : dynamics of the very early phase ✦ origin? → 1) dynamically unstable initial condition? 2) mis-alignment of (global) B-field and rotation axis? Tobin et al. (2010) 12
Low-mass SF II: Theory ✦ “c2d” MHD simulation: longer time calc. w/ a sink particle (Machida’s talk) ✦ circumstellar disk-> originates in the flattened first core ✦ second core(=protostar) is formed in the center of the first core ✦ in the early phase, “proto”circumstellar disk is massive and grav. unstable → formation of first planet? Inutsuka et al. (2010) ✦ “c2d” MHD simulation II (Duffin’s talk) ✦ discovery of warped disk and precession of jet in a single star formation ✦ very new discovery, mechanism unidentified yet ✦ precession may not be an indicator of binary 13
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