constraints on small grains from iso, spitzer data: towards predicting the cm-emission of pahs l....
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Constraints on small grains from ISO, Spitzer data:
Towards predicting the cm-emission of PAHs
L. VerstraeteN. Flagey IAS, OrsayM. Compiègne
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Interstellar Dust EmissionInterstellar Dust Emission
BGs:a ~ 0.1 mPAHs:
a ~ 0.5 nm
VSGs: a~10 nm
3.3
Boulanger 2000
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Diffuse medium by Spitzer-IRAC Diffuse medium by Spitzer-IRAC
Flagey et al. 2005
NIR continuum:
- Teff ~ 1100 K
- Not correlated to PAHs
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Dust Emission MechanismDust Emission Mechanism
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Interstellar ExtinctionInterstellar Extinction
220 nmUV
visible
Lutz et al. 96
220 nm bump -->
Graphite
n(a) ~ a-(MRN, Kim & Martin)
[C]dust
< 200 ppm
•9.7 & 18 m bands
•--> Silicates
•[Si]dust
< 36 ppm
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Dust ModelDust Model
CLOUDY 96.01: since 2003 include grain physics (beside gas)
Easy access to dust optical constants + Mie code (n,k)
Versatile n(a)
Full radiation field (10 cm to X-rays)
Accurate T-fluctuations
Grain charge and gas-grain interactions (drift velocities)
Simple geometry and transfer (forward/backward)
- Full Dust model in ~1' / zone, 6' for Av=1, 15' for Av=5
- Only emergent spectrum
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Main Updates / DMain Updates / Déésert et al. modelsert et al. model
1) T-fluctuations well-treated
2) Realistic opt. properties Graphite and Silicates
(Draine web site)
3) New Standard model for Cirrus: 180 ppm C 33 ppm Si
PAHs: a = 0.4 – 0.6 nm, bands from ISO-SWS
VSGs: graphite a = 1 – 5 nm
BGs: graphite a = 10 – 250 nm, silicates a = 0.35 – 250 nm
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Weingartner & Draine 2001
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= 1400 nH ~ 104 cm-2
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[PAH] / 4
~ 27,000 nH ~ 104 cm-2
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Submm/cm Emission of PAHs Submm/cm Emission of PAHs
Depends on P(T): C(T)and FIR
--> f(a)
ISO spectra
PAH band profiles
Drude
1.24
C10
H8
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Diffuse ISM
Spitzer IRS
new bands @ 17.1, 19 m ....
Smith et al. 2004
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Modest Impact on SEDs
+ rotating PAHs -- > N. Ysard's talk
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DrudeC10
H8
1.24
Influence of FIR cross-section on P(T)Influence of FIR cross-section on P(T)
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SummarySummary
CLOUDY 96.01 and up: - versatile tool to model dust emission in diffuse ISM,- T-fluctuations well treated
Dust model for a variety of regions: ~ 1 – 3 104
[C] = 180 ppm n ~ 102 – 104 cm-3
[Si] = 35 ppm PAHs small: 20 -
50 C
FIR cross-section of PAHs important for:
- vibrational emission
- T-fluctuation --> rotational emission
Next:
- Subtract the PAHs and study the VSG SED (M. Compiegne)
- Take charge into account (small PAHs well studied)
- Add the contribution of spinning PAHs (N. Ysard)
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log N
H (cm-2) = 14, 20, 21, 22
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6.27.7 11.3
~ 105
~ 103
Interfaces photodissociéesInterfaces photodissociées
Flux de photons: ~ 103 - 105
Densité du gaz:
nH ~ 103 – 104 cm-3
Spectres ISO-SWS
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Lorentz
Bound e- ~ x
Drude ~ x2
Gauss
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~ 1400 n ~ 104 cm-3
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