Differences
This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revision | ||
|
ohp_meeting_september_2018 [2018/09/22 22:07] admin-mist |
ohp_meeting_september_2018 [2018/09/22 22:17] (current) admin-mist |
||
|---|---|---|---|
| Line 1: | Line 1: | ||
| + | ==== Presentations ==== | ||
| + | |||
| + | {{ :ohp_lehmann.pdf |Andrew}} | ||
| + | {{ :ohp-lesaffre.pdf |Pierre L}} | ||
| + | {{ :mist-ohp.pdf |François L}} | ||
| + | |||
| + | ==== Notes taken by FL ==== | ||
| + | |||
| **EDITH FALGARONE | **EDITH FALGARONE | ||
| ** | ** | ||
| Line 115: | Line 123: | ||
| * Maps of centroid velocity increment extrema highly non-Gaussian (filamentary) | * Maps of centroid velocity increment extrema highly non-Gaussian (filamentary) | ||
| - | {{ ::a45bd86b38b18112daee0f079839d325.jpg?400 |}} | + | {{ ::a45bd86b38b18112daee0f079839d325.jpg?600 |}} |
| **ERWAN ALLYS | **ERWAN ALLYS | ||
| Line 123: | Line 131: | ||
| * A second reduction is related to physics (isotropy, rotations) : ended up with about 70 coefficients | * A second reduction is related to physics (isotropy, rotations) : ended up with about 70 coefficients | ||
| * Power spectrum does not care whether a scale appears in conjunction with another or not. | * Power spectrum does not care whether a scale appears in conjunction with another or not. | ||
| + | |||
| + | **ELENA BELLOMI | ||
| + | ** | ||
| + | * Dynamical evolution of matter in the ISM is accompanied by a chemical evolution, and chemistry has in turn an impact on the dynamics (cooling) | ||
| + | * Interest in the diffuse ISM : partly ionized, partly molecular, turbulent | ||
| + | * Equipartition of energies | ||
| + | * Theoretical approaches : dynamical simulations / PDR models and TDR models for chemical evolution. Scales to model : from large scales 50-100 pc to dissipation scales (not resolvable) | ||
| + | * Numerical simulations : dissipation is numerical | ||
| + | * Astrochemical models | ||
| + | * Out-of-equilibrium chemically or thermally. Timescales for equilibria can be very different. Usually assuming chemical steady-state, driven by kinetics, not by thermodynamics. | ||
| + | * Focus on H2 chemistry : formation time is particularly long, influence on dynamics through heating (exothermic formation) and cooling (lines, also from C+, O, Lyman alpha) | ||
| + | * Photodissociation of H2 0.4 eV | ||
| + | * Heating and cooling curve : net loss L=n^2\lambda(T)-n\Gamma —> thermal instability curve, depending on mostly G0 and abundances of PAHs | ||
| + | * Simulations : perdiodic boundary conditions, isotropic turbulent forcing in Fourier space, no thermal conduction, no gravity. H2 formation and destruction computed on the fly. | ||
| + | * Two fluids (H and H2) plus a prescription for C+, O, for cooling. | ||
| + | * H2 treated out of equilibrium because timescale for reaching steady-state for H2 is long and determines the timescales for other species. | ||
| + | * Large fraction of the gas is out of equilibrium thermally | ||
| + | * N(H2) vs N_H shows bimodal distribution : transition H -> H2 with self-shielding of H2 leas to phase transition | ||
| + | * Different setups in density, G0, forcing amplitude, B field, resolution and box size. | ||
| + | * Separation of voxels in <300K, 300K-3000K,>3000K | ||
| + | * Influence of initial density : the larger, the more CNM in the « final » state. | ||
| + | * G0 increase leads to decrease of f(H2) by increased photodissociation | ||
| + | * Turbulence increase pushes more gas away from the thermal equilibrium curve. | ||
| + | * Increase of B prevents the formation of dense structures. | ||
| + | |||
| + | |||
| + | ==== Afterthoughts by BG ==== | ||
| + | |||
| + | Starting with the idea that the ISM is a multiphase turbulent medium, several observations | ||
| + | may help us to understand | ||
| + | * Pierre's shear | ||
| + | * Edith's starburst | ||
| + | |||
| + | |||
| + | |||
| + | I'm no observer so I'll just throw ideas even if they are ridiculous or not completely correct | ||
| + | |||
| + | • To trace the multiphase ISM | ||
| + | - - HI maps (mass of WNM+CNM) | ||
| + | - - ArH+ (tracer of purely atomic gas -> even better tracer than HI) | ||
| + | - - CII and OI fine structure (set the global thermal balance of CNM -> mass of CNM) | ||
| + | - - CII and OI metastable lines (trace the mass of WNM) | ||
| + | - - CI fine structure lines | ||
| + | - -> gives a measure of the gas thermal pressure | ||
| + | - -> may give the mass of unstable gas | ||
| + | - -> its relation with CO gives strong constrain on chemical models | ||
| + | - - CS, C2H, OH, and H2O (tracers of PDR in diffuse ISM) | ||
| + | - - HF (tracer of H2) | ||
| + | - - CH (tracer of PDR, except maybe at small column densities) | ||
| + | - - OH+ and H2O+ (tracers of CR ionization and molecular fraction) | ||
| + | |||
| + | |||
| + | • To trace the dissipation of turbulent energy at small scales and / or the turbulent mixing of phases at all scales | ||
| + | - - CH+ and SH+ | ||
| + | - - excited H2 | ||
| + | - - HCO+ and CO | ||
| + | - - CH (anomaly with PDR predictions at small column densities) | ||
| + | - - SH (not sure) | ||
| + | |||
| + | |||
| + | • For the DENSE GAS in starburst galaxies, we could try | ||
| + | - - SH+ | ||
| + | - - the rotational diagram of CH+ (as high as possible) -> this would be new by the way | ||
| + | - - CO, OH or H2O which behave oppositely to CH+ in irradiated shocks. | ||