when meets IR the clouds hiding behind the dust & cosmic rays Isabelle Grenier Jean-Marc Casandjian Régis Terrier AIM, Service d’Astrophysique, CEA Saclay
when meets IRthe clouds hiding behind the dust &
cosmic rays
when meets IRthe clouds hiding behind the dust &
cosmic rays
Isabelle GrenierJean-Marc Casandjian
Régis TerrierAIM, Service d’Astrophysique, CEA Saclay
atomic & molecular gasatomic & molecular gas
• CO survey from
Dame et al. ‘01
• Leiden-Dwingeloo 21 cm line survey at > -30°
• Dickey-Lockman 21 cm at < -30°
100 µm dust emission100 µm dust emission
• IRAS 100 µm calibrated using DIRBE Schlegel ‘98
dust reddening & 94 GHz emissiondust reddening & 94 GHz emission
• IRAS 100µm + DIRBE + DMR + FIRAS
=> Idust at 94GHz for
2.70 B(16.2K)
+ 1.67 B(9.2K)Finkbeiner ‘99
• IRAS 100µm + DIRBE 240µ/100µ => Ndust for
uniform ² B(18.2K)
• Ndust scaled to E(B-V)
from external galaxiesSchlegel ’98
rays above 100 MeV rays above 100 MeV
• Compton-EGRET interstellar radiation
( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( )[ ]∫∫
∫∫′′ρ′+ρ′′ρ
+′′ρ′ρ=π
dsEdE,sE,EqsE,Eq.s,E
dsEdE,Eqss,EE,b,lI
ISRFICgasBe
gasp 0
the local interstellar modelthe local interstellar model
• |b| > 5° or 10° cosmic-ray density ~ uniform at D < 0.5-1 kpc
interstellar fitinterstellar fit
• warm dust • cold dust
HI+CO+EBV
HI+CO+I100µ
HI+CO
EBV
I100µ
1 55
71 298
39713 530
HI+CO+I94GHz
242
458I94GHz
2 ln
(L)
HI+CO+EBV
HI+CO+I100µ
HI+CO
EBV
I100µ
3936
20
116
HI+CO+I94GHz
15
21I94GHz
~
fit improvementsfit improvements
IC emission from the coldest dust <<
WCObNHIa)VB(E −−−
WCObNHIa)GHz(I −−94
WCObNHIa)µ(I −−100
-ray excess
fit improvementfit improvement
H2 / dark / dense HI matriochkasH2 / dark / dense HI matriochkas
l0 = 70°
351
151
−≈
≈
.R
R
.R
R
CO
dark
dark
HI
movies at http://dphs10.saclay.cea.fr/Sap/Actualites/Breves/grenier050217/images/
local gas reserveslocal gas reserves
• opt. thin HI
• qHI ≈ qdark
X > 100 MeV = 1.74 ± 0.04
X > 300 MeV = 1.61 ± 0.03
1020 H2 cm-2 K-1 km-1 s
line-of-sight
average densities
2210 Hdark
denseHIdark
n.n
nn
×≈≈
dark cloudsdark clouds
• low, but enough shielding– using AV /E(B-V) = 3.1
• normal metallicity 1221
12212
1221
102053
102807232
10220176
−−
−−
−−
±=⎥⎦
⎤⎢⎣
⎡−
±=⎥⎦
⎤⎢⎣
⎡−
±=⎥⎦
⎤⎢⎣
⎡−
magcm)..()VB(E
NH
magcm)..()VB(E
)H(N
magcm)..()VB(E
NH
dark
CO
HI
anomalous dustanomalous dust
• anomalous dust emission Bennett ’03, Lagache ‘04
– from spinning dust?
– not local synchrotron variations
Spectral Index (408 MHz, 23 GHz)
-2.3-3.4
94 GHz
cold HI or cold H2 ?cold HI or cold H2 ?
• maybe HI– ndark ≈ nCNM
– Rdark ≈ RdenseHI
– but
• maybe H2
– enough Av
– [NH/E(B-V)] close to the CO one
enough grains to form H2
– cold environment (Tdust ~ 10 K)
– H2 absorption lines without CO
around Cham (Gry ‘02)
=> nHI+2nH2 ~ 50 H cm-3
=> 2N(H2)/NHtot = 50-70%
– H2 absorption lines without CO
in cirrus clouds (Reach ‘94)
any CO detection?any CO detection?
• beam diluted tiny clumps for WCO < 2 K km/s
any CO detection?any CO detection?
• why not? too cold? Tdust ~ 10 K, densities to low?
• only tips of icebergs seen
dark vs. H2 and HI massdark vs. H2 and HI mass
• mass ratios ind. of distance
• Mdark/MCO ↓ with MCO
6:1:6
5:1:5
2:1:2.7 0.6:1:3
0.2:1:0.5
0.7:1:1
0.7:1:3
CO:dark:HI
dark vs. H2 and HI massdark vs. H2 and HI mass
• locally
• Mdark/MCO ↓ with MCO
5040 .denseHIdark
.COdark MMMM ∝∝Mdark ~ 2 105 M
MH2-CO ~ 6 105 MMdenseHI ~ 7 105 MMdark/MCO ~ 30-35 %Mdark/MdesnHI ~ 26-30 %
local ISM biased tolarge H2 clouds
OBass, HII
OBass, HII
little small-star formation
lot of small-star formation
older OBass, HII
CO mass spectrum in the Milky WayCO mass spectrum in the Milky Way
• in the outer galaxy– complete down to 500 M – and up to D < 10 kpc
• in the inner Galaxy & centerhigher masses sampledWilliams & McKee ’97 Miyasaki ‘00
for 103 ≤ MCO ≤ 106M
more if 500 M or flatter Mdk(McO)
dN/dM
M-1.8 ± 0.03
Heyer ‘01
Miyasaki ‘00
6191 ..MdM
dN−≤α≤−∝ α
α -1.6 -1.8 -1.9 -2.0
Mdk/MCO 0.6 0.9 1.1 1.4
X ratioX ratio
• X = N(H2) / W(CO) = qCO/2qHI if nCR(HI)~nCR(H2)
– no virial equilibrium or gas/dust assumption,
– but small bias from structured IC emission ← e- + far-IR field
Cloud RGal (kpc)
X in 1020 mol. cm-2 K-1 km-1 s
Ophiuchus 8.4 1.1 ± 0.2 Local average at |b| > 5°: 1.61 ± 0.04 (>100 MeV)
1.73 ± 0.03 (>300 MeV)
1.8 ± 0.3 (I100µ Dame ’01)
Taurus 8.6 1.08 ± 0.10
Cepheus 8.7 0.92 ± 0.14 Galactic average: 1.9 ± 0.2 (Strong ’96) 1.56 ± 0.05 (Hunter ’97)
Orion 8.9 1.35 ± 0.15
Monoceros 9.2 1.64 ± 0.31 larger X in the outer Galaxy