when  meets IR the clouds hiding behind the dust & cosmic rays

when  meets IRthe clouds hiding behind the dust & cosmic rays Isabelle Grenier Jean-Marc Casandjian Régis Terrier AIM, Service d’Astrophysique, CEA Saclay

atomic & 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 emission • IRAS 100 µm calibrated using DIRBE Schlegel ‘98

dust 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 galaxies Schlegel ’98

 rays above 100 MeV • Compton-EGRET interstellar radiation

the local interstellar model • |b| > 5° or 10° cosmic-ray density ~ uniform at D < 0.5-1 kpc

HI+CO+EBV HI+CO+EBV HI+CO+I94GHz HI+CO+I94GHz 1 557 39 36 1 298 EBV EBV 21 458 I94GHz I94GHz 397 20 HI+CO+I100µ HI+CO+I100µ 15 242 ~  2 ln(L) HI+CO HI+CO 13 530 116 I100µ I100µ interstellar fit • warm dust  • cold dust 

IC emission from the coldest dust << -ray excess fit improvements

fit improvement

H2 / dark / dense HI matriochkas movies at http://dphs10.saclay.cea.fr/Sap/Actualites/Breves/grenier050217/images/ l0 = 70°

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 local gas reserves

dark clouds • low, but enough shielding • using AV /E(B-V) = 3.1 • normal metallicity

Spectral Index (408 MHz, 23 GHz) -3.4 -2.3 b anomalous dust • anomalous dust emission Bennett ’03, Lagache ‘04 • from spinning dust? • not local synchrotron variations 94 GHz

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) cold HI or cold H2 ?

any CO detection? • beam diluted tiny clumps for WCO < 2 K km/s

any CO detection? • why not? too cold? Tdust ~ 10 K, densities to low? • only tips of icebergs seen

CO:dark:HI 0.7:1:1 5:1:5 0.2:1:0.5 6:1:6 0.7:1:3 2:1:2.7 0.6:1:3 dark vs. H2 and HI mass • mass ratios ind. of distance • Mdark/MCO↓ with MCO

OBass, HII little small-star formation OBass, HII older OBass, HII lot of small-star formation dark vs. H2 and HI mass • locally • Mdark/MCO↓ with MCO Mdark ~ 2 105 M MH2-CO ~ 6 105 M MdenseHI ~ 7 105 M Mdark/MCO ~ 30-35 % Mdark/MdesnHI ~ 26-30 % local ISM biased to large H2 clouds

in the outer galaxy complete down to 500 M and up to D < 10 kpc in the inner Galaxy & center higher masses sampled Williams & McKee ’97 Miyasaki ‘00 for 103 ≤ MCO ≤ 106M more if 500 M or flatter Mdk(McO) Miyasaki ‘00 CO mass spectrum in the Milky Way dN/dM  M-1.8 ± 0.03 Heyer ‘01

X 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

when  meets IR the clouds hiding behind the dust & cosmic rays