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Dust cycle through the ISM

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 ISM. a few 10 7 yrs. Molecular Clouds. CNM WNM WIM. cloud enveloppes

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Dust cycle through the ISM

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

  2. Dust Cycling in Galaxies Diffuse ISM a few 107 yrs Molecular Clouds • CNM • WNM • WIM • cloud enveloppes • dense cores Low mass stars Giants Star Formation 3 109 yrs 109 yrs SN 3 106 yrs Massive stars

  3. 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 109 yrs)

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

  5. 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

  6. Variations in PAH abundance

  7. Dust in the Spica HII region

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

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

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

  11. Model with dust evolution (Stepnik et al. 2002) Change of dust properties at : - r < 4’ ± 1’ - Av = 2.1 ± 0.5 • Small grainabundance : 0.1±0.1 • Submmemissivity : 3.4+0.3-0.7 • Tcentre = 12.0 K 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

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

  13. tFIR / AV Ratio Cold Dust Polaris Diffuse ISM Schlegel et al. Cambresy et al. 2002

  14. Enhancing the FIR/mm dust emissvity tFIR/NH = Md/NH * 1/rg * <3*Qext/4a> => For a fixed dust to gas ratio (Md/NH ), higher values of tFIR/NH for fluffy grains (lower rg ) and/or higher < Qext/a> (composite grains?) carbon silicates composite Dwek 1997

  15. FIR to mm dust emissivity in the diffuse ISM <NHI> t(250mm)/NHI t(250mm)/NHI Boulanger et al. 1996

  16. mm dust emissivityin the diffuse ISM • t (1.2mm) / NH = 5.0 +/- 0.9 10-27 cm2 • Error bar = contribution from dust in H2 and HII (WIM) gas • Corresponds to a opacity per dust mass : k (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/NH ratio)

  17. FIR to mm emissivity in the diffuse ISM

  18. Structure and temperature effect Silicates amorphous crystalline Agladze et al. (1996)

  19. Summary Interstellar dust observations are bringing an original perpspective on the ISM: • Interstellar dust nature and evolution • Its role as as a tracer of the • ISM structure (disks, protostellar cores but also HI-H2 transition in the diffuse ISM and PDRs) • Magnetic Field (polarisation) • and an actor of ISM evolution Sub-mm wavelengths still at exploration stage => Herschel More talks on Friday morning ...

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