Constraints on small grains from ISO, Spitzer data:

Towards predicting the cm-emission of PAHs

L. VerstraeteN. Flagey IAS, OrsayM. Compiègne

Interstellar Dust EmissionInterstellar Dust Emission

BGs:a ~ 0.1 mPAHs:

a ~ 0.5 nm

VSGs: a~10 nm

3.3

Boulanger 2000

Diffuse medium by Spitzer-IRAC Diffuse medium by Spitzer-IRAC

Flagey et al. 2005

NIR continuum:

- Teff ~ 1100 K

- Not correlated to PAHs

Dust Emission MechanismDust Emission Mechanism

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

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

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

Weingartner & Draine 2001

= 1400 nH ~ 104 cm-2

[PAH] / 4

~ 27,000 nH ~ 104 cm-2

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

Diffuse ISM

Spitzer IRS

new bands @ 17.1, 19 m ....

Smith et al. 2004

Modest Impact on SEDs

+ rotating PAHs -- > N. Ysard's talk

DrudeC10

H8

1.24

Influence of FIR cross-section on P(T)Influence of FIR cross-section on P(T)

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)

log N

H (cm-2) = 14, 20, 21, 22

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

Lorentz

Bound e- ~ x

Drude ~ x2

Gauss

~ 1400 n ~ 104 cm-3