Dust cycle through the ISM

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
Molecular Clouds
a few 107 yrs

• 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

gt 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
gt 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
Av3.5 mag, D140 pc
11
Model with dust evolution

• Change of dust properties at
• - r lt 4 1
• - Av 2.1 0.5
• Small grainabundance
• 0.10.1
• Submmemissivity
• 3.4 0.3-0.7
• Tcentre 12.0 K

(Stepnik et al. 2002)
Similar conclusion reached for translucent
molecular cirrus(e.g. Polaris flare Bernard et
al. 1999, AA 347, 640)
J.P. Bernard, Herschel GP KP, Paris, June 16th 04
12
PRONAOS observations in the Polaris flare
Av 0.8 mag
Av 0.2 mag
(Bernard et al. 1999, AA 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 lt3Qext/4agt gt For a
fixed dust to gas ratio (Md/NH ), higher values
of tFIR/NH for fluffy grains (lower rg ) and/or
higher lt Qext/agt (composite grains?)
carbon
silicates
composite
Dwek 1997
15
FIR to mm dust emissivity in the diffuse ISM
ltNHIgt
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 gt
Herschel
More talks on Friday morning ...