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