Constraints on small grains from ISO, Spitzer data: Towards predicting the cm-emission of PAHs L. Verstraete N. FlageyIAS, Orsay M. Compiègne

Interstellar Dust Emission BGs : a ~ 0.1  m PAHs: a ~ 0.5 nm VSGs: a~10 nm 3.3    Boulanger 2000

Diffuse medium by Spitzer-IRAC Flagey et al NIR continuum: - Teff ~ 1100 K - Not correlated to PAHs

Dust Emission Mechanism

Interstellar Extinction 220 nm UV visible Lutz et al nm bump--> Graphite n(a) ~ a -  (MRN, Kim & Martin) [C] dust < 200 ppm 9.7 & 18  m bands -->Silicates [Si] dust < 36 ppm

Dust 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 / Désert 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 C33 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

 = 1400n H ~ 10 4 cm -2

[PAH] / 4  ~ 27,000 n H ~ 10 4 cm -2

Submm/cm Emission of PAHs Depends on P(T):C(T)and  FIR -->f(a) ISO spectra PAH band profiles Drude 1.24 C 10 H 8

Diffuse ISM Spitzer IRS new 17.1, 19  m.... Smith et al. 2004

Modest Impact on SEDs + rotating PAHs -- > N. Ysard's talk

Drude C 10 H Influence of FIR cross-section on P(T)

Summary CLOUDY and up: - versatile tool to model dust emission in diffuse ISM, - T-fluctuations well treated Dust model for a variety of regions:  ~ 1 – [C] = 180 ppmn ~ 10 2 – 10 4 cm -3 [Si] = 35 ppm PAHs small: 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

 ~ 10 5  ~ 10 3 Interfaces photodissociées Flux de photons:  ~ Densité du gaz: n H ~ 10 3 – 10 4 cm -3 Spectres ISO-SWS

Lorentz Bound e - ~ x Drude ~ x 2 Gauss

 ~ 1400 n ~ 10 4 cm -3