Dust cycle through the ISM Francois Boulanger Institut d ’Astrophysique Spatiale Global cycle and interstellar processing Evidence for evolution Sub-mm perspective

Dust Cycling in Galaxies Diffuse ISMMolecular Clouds CNM WNM WIM Star Formation SN 10 9 yrs a few 10 7 yrs yrs yrs Massive stars Low mass stars Giants cloud enveloppes dense cores

Dust Evolution: Physical Processes Photo-processing/destruction Amorphization by cosmic rays Grain shattering/sputtering in fast supernovae shocks (WNM, WIM) Grain shattering in turbulent clouds (CNM) Grain coagulation (CNM) Act on time scales shorter than replenishment time by dying stars (a few 10 9 yrs)

Dust Spectral Energy Distribution Comp. Power Mass PAH 18% 6% VSG 15% 6% BG 67% 88%

Dust Evolution: Evidence Variations in PAH abundance in the diffuse ISM and PDRs Enhanced VSG abundance in low density gas: the Spica HII region Cold dust associated with dense molecular gas: lower temperature, larger far-IR emissivity and no small grains => From the diffuse ISM to molecular clouds, PAHs to large grains

Variations in PAH abundance

Dust in the Spica HII region

Dust SED/Composition => Enhanced VSG abundance factor ~ 5 : shock processing ?

L1780 translucent cloud (Av~ 2) Gradual change in grain size distribution Not a systematic edge to center effect

PRONAOS Cut Sub-mm Observations Taurus Filament Av=3.5 mag, D=140 pc

Model with dust evolution Change of dust properties at : - r < 4’ ± 1’ - A v = 2.1 ± 0.5 Small grain abundance : 0.1±0.1 Submm emissivity : T centre = 12.0 K (Stepnik et al. 2002) Similar conclusion reached for translucent molecular cirrus (e.g. Polaris flare: Bernard et al. 1999, A&A 347, 640) J.P. Bernard, Herschel GP KP, Paris, June 16th 04

Av = 0.2 mag Av = 0.8 mag (Bernard et al. 1999, A&A 347, 640) Standard cirrus: 17.5 K,  =2.0 Polaris cirrus: 13.0 K,  =2.2 PRONAOS observations in the Polaris flare

 FIR / A V Ratio Cambresy et al Diffuse ISM Schlegel et al. Cold Dust Polaris

Enhancing the FIR/mm dust emissvity  FIR /N H = M d /N H * 1/  g * => For a fixed dust to gas ratio (M d /N H ), higher values of  FIR /N H for fluffy grains (lower  g ) and/or higher (composite grains?) Dwek 1997 carbon silicates composite

FIR to mm dust emissivity in the diffuse ISM  (250  m)/N HI Boulanger et al. 1996

mm dust emissivityin the diffuse ISM  (1.2mm) / N H = 5.0 +/ cm 2 Error bar = contribution from dust in H2 and HII (WIM) gas Corresponds to a opacity per dust mass :  (1.2mm) = 0.30 cm2/g Comparable to the value in Draine and Lee (1984) model and observations of the Bok globule B68 (Bianchi et al. Assuming a diffuse ISM Av/N H ratio)

FIR to mm emissivity in the diffuse ISM

Structure and temperature effect Agladze et al. (1996) Silicates amorphouscrystalline

Summary Interstellar dust nature and evolution Its role as as a tracer of the > ISM structure (disks, protostellar cores but also HI-H 2 transition in the diffuse ISM and PDRs) > Magnetic Field (polarisation) and an actor of ISM evolution Interstellar dust observations are bringing an original perpspective on the ISM: More talks on Friday morning... Sub-mm wavelengths still at exploration stage => Herschel