the meudon pdr code on mhd simulations f. levrier p. hennebelle, e. falgarone, m. gerin, b. ooghe...
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![Page 1: The Meudon PDR code on MHD simulations F. Levrier P. Hennebelle, E. Falgarone, M. Gerin, B. Ooghe (LERMA - ENS) F. Le Petit (LUTH - Observatoire de Paris)](https://reader036.vdocuments.mx/reader036/viewer/2022062322/56649ed35503460f94be2b08/html5/thumbnails/1.jpg)
The Meudon PDR code on MHD simulations
F. LevrierP. Hennebelle, E. Falgarone, M. Gerin, B. Ooghe
(LERMA - ENS)
F. Le Petit(LUTH - Observatoire de Paris)
J. R. Goicoechea(CAB)
STAR FORMAT meeting, Heidelberg, 4-5 may 2010
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A case study : The [CII] 158 µm line
Fine structure of the ground state of C+Fine structure of the ground state of C+ UV to IR energy transfer via photoelectric effectUV to IR energy transfer via photoelectric effect
UVUV
electronselectrons
dust
IR ContinuumIR Continuum
gasgas
Cooling Cooling lineslines
• Carbon ionization potential : 11.3 eV• One of the dominant cooling lines of interstellar gas• Early stages of star formation • 0.3% of the bolometric FIR emission of the Galaxy (Wright et al. 91)• Seen “everywhere”
SPICA / SAFARI (Joint JAXA / ESA)
Bennett et al. 94 (COBE / FIRAS)
Nakagawa et al. 98 (BICE)
Makiuti et al. 2002 (FILM / IRTS)
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A very crude method
• Sample lines of sight in the MHD simulation cubes
• Extract “clouds” by applying a simple density
threshold
• Use these as input density profiles in the Meudon
PDR code• Derive 158 µm line intensity vs. HI column density
• Estimate Total gas vs HI relationship
• Build line emission map from simulated cube
• Estimate time required to map the sky area
covered
Technical stuff
Scientific stuff
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Compressible MHD turbulence simulationsHennebelle et al. 2008
50 pc
• RAMSES code (Teysier 2002, Fromang et al. 2006)• Adaptive Mesh Refinement with up to 14 levels• Converging flows of warm (10,000 K) atomic gas• Periodic boundary conditions on remaining 4 sides• Includes magnetic field, atomic cooling and self-gravity consistently• Covers scales 0.05 pc - 50 pc• Heavy computation : ~30,000 CPU hours ; 10 to 100 GB
X-Y column density X-Y density cut X-Y temperature cut
cold clumpscold clumps
warm turbulent warm turbulent interclump mediuminterclump medium
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Line of sightLine of sight
Total gas column densityTotal gas column density
Density structures along the line of sight
Total gas density cutTotal gas density cut
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1 2 3
1-3
Applying the PDR code on clumps
UVUV
C+C+ CC COCO C+C+CC
For each “clump” 1 to 3 and full 1-3 region
For each “clump” 1 to 3 and full 1-3 region
UVUV
RAMSES ASCIIEnd
products(plots,...)
IDL
.pfl file
pdr.in file
+{ }F90
{FITS file
XML file
+
PDR
}PDR
Analyzer
Convergence issues in low density regions Heavy computations : a few hours per “clump”
Apply code on overdensities only
Grid computation would be ideal
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Simulation results
1 2 3
1-3
1
2
3
1-3
0
0.5
1.0
1.5
2.0
2.5
3.5
3.0
4.0
4.5
5 6 7
8
Integrated emissivity of the [CII] lineIntegrated emissivity of the [CII] lineHI column densityHI column density
1D geometry unrealistic
3D PDR code badly needed
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Illumination of clouds
2-ray approximation
1 2
18-ray approximation
1 2
3
45
6
7
8
(in each of XY, XZ, YZ planes)
(1D : same as PDR code)
• “Fractal” nature of ISM clouds / Simulated density structures • Each point may be illuminated from many directions• At each point, from each line of sight, compute visual extinction• Minimum value taken to be “actual” extinction
Do this as post-processingUse it for incoming field in PDR code
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Illumination of clouds : resultsExample on a 2D
cut
18-ray approximation
2-ray approximation 8
1.5
•Total extinction•Morphology
Example on a single line of sight
Exctintion up to 20 times lower
Note effect on :
2-ray approximation