molecular tracers of turbulent shocks in molecular clouds
DESCRIPTION
Molecular Tracers of Turbulent Shocks in Molecular Clouds. Andy Pon, Doug Johnstone , Michael J. Kaufman. ApJ , submitted May 2011 . 12 CO J = 1-0. Observed (FWHM = 1.9 km / s ). Thermal broadening alone (FWHM = 0.2 km / s ). Ridge et al. (2006). - PowerPoint PPT PresentationTRANSCRIPT
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Molecular Tracers of Turbulent Shocks in Molecular
Clouds
Andy Pon, Doug Johnstone,Michael J. Kaufman
ApJ, submitted May 2011
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Ridge et al. (2006)
Observed(FWHM = 1.9 km / s)
Thermal broadening alone(FWHM = 0.2 km / s)
12CO J = 1-0
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Sound Crossing Times (t / ts)
Turb
ulen
t Ene
rgy
(E/ρ
L3 C
s2 )
Stone et al. (1998)
Turbulent Energy Decay in a Hydro Simulation
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B = 14 μG
B = 1.4 μG
B = 4.4 μG
B = 0 μG
Stone et al. (1998)
Turb
ulen
t Ene
rgy
(E/ρ
L3 C
s2 )
Sound Crossing Times (t / ts)
Turbulent Energy Decay in MHD Simulations
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Shock Model Setup Magnetohydrodynamic (MHD) C-shock code from
Kaufman & Neufeld (1996) Density of either 102.5, 103 or 103.5 cm-3
Shock velocities of 2 or 3 km / s Initial magnetic field strengths, perpendicular to
the shock direction, of B = b n(H)0.5 μG, where b = 0.1 or 0.3. This gives B from 3 μG to 24 μG.
Mach numbers from 10 to 20 and Alfvénic Mach numbers ranging from 5 to 15
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n = 102.5 cm-3 n = 103 cm-3 n = 103.5 cm-3
v = 3 km s-1
b = 0.3
v = 2 km s-1
b = 0.1
v = 3 km s-1
b = 0.1
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Energy Dissipation Mechanisms
CO Rotational Transitions (68%)
Magnetic Field (16%)
H2 Rotational Transitions (14%)H2 Rotational Transitions (14%)
S(0) at 28 μm and
S(1) at 17 μm
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Molecular Cloud Dissipation Rate The turbulent energy density is:
E = 3/2 ρv2
If the dissipation timescale is roughly the crossing time:
ΔE / tc = 3/2 ρv2 * v / (2R)
There is an empirical relationship between the velocity dispersion and the radius of a molecular cloud.
For a spherical cloud:
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Photodissociation Region (PDR) Model
PDR model from Kaufman et al. (1999) Density of 1000 cm-3 Interstellar radiation field of 3 Habing Microturbulent Doppler line width of 1.5 km / s Extends to an AV of approximately 10
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5-4
6-5
7-6 8-7
Zeus-2 Bands
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n = 102.5 cm-3 n = 103 cm-3 n = 103.5 cm-3
v = 3 km s-1
b = 0.3
v = 2 km s-1
b = 0.1
v = 3 km s-1
b = 0.1
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Summary (see ApJ, submitted May 2011 for more detail)
Magnetic field compression removes a significant (15-45%) fraction of a shock’s energy
H2 rotational lines trace shocks with Alfvénic Mach numbers > 15
CO rotational transitions dissipate the majority of the energy
Low J lines are dominated by PDR emission Mid to high lines trace shock emission!