when  meets IR the 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 DIRBESchlegel ‘98

dust reddening & 94 GHz emission IRAS 100µm + DIRBE + DMR + FIRAS => I dust at 94GHz for 2.70 B (16.2K) B (9.2K) Finkbeiner ‘99 IRAS 100µm + DIRBE 240µ/100µ => N dust for uniform ² B (18.2K) N dust 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 < kpc

interstellar fit warm dust  cold dust  HI+CO+EBV HI+CO+I100µ HI+CO EBV I100µ HI+CO+I94GHz I94GHz 2 ln(L) HI+CO+EBV HI+CO+I100µ HI+CO EBV I100µ HI+CO+I94GHz I94GHz ~ 

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

fit improvement

H 2 / dark / dense HI matriochkas l 0 = 70° movies at

local gas reserves opt. thin HI q HI ≈ q dark X > 100 MeV = 1.74 ± 0.04 X > 300 MeV = 1.61 ± H 2 cm -2 K -1 km -1 s line-of-sight average densities

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

anomalous dust anomalous dust emission Bennett ’03, Lagache ‘04 –from spinning dust? –not local synchrotron variations Spectral Index (408 MHz, 23 GHz)  GHz

cold HI or cold H 2 ? maybe HI –n dark ≈ n CNM –R dark ≈ R denseHI –but maybe H 2 –enough A v –[NH/E(B-V)] close to the CO one enough grains to form H 2 –cold environment (T dust ~ 10 K) –H 2 absorption lines without CO around Cham (Gry ‘02) => n HI +2n H2 ~ 50 H cm -3 => 2N(H 2 )/NH tot = 50-70% –H 2 absorption lines without CO in cirrus clouds (Reach ‘94)

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

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

dark vs. H 2 and HI mass mass ratios ind. of distance M dark /M CO ↓ with M CO 6:1:6 5:1:5 2:1: :1:3 0.2:1: :1:1 0.7:1:3 CO:dark:HI

dark vs. H 2 and HI mass locally M dark /M CO ↓ with M CO M dark ~ M  M H2-CO ~ M  M denseHI ~ M  M dark /M CO ~ % M dark /M desnHI ~ % local ISM biased to large H 2 clouds OBass, HII little small-star formation lot of small-star formation older OBass, HII

CO 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 & center higher masses sampled Williams & McKee ’97 Miyasaki ‘00 for 10 3 ≤ M CO ≤ 10 6 M  more if 500 M  or flatter M dk (M cO) dN/dM  M -1.8 ± 0.03 Heyer ‘01 Miyasaki ‘00  M dk /M CO

X ratio X = N(H 2 ) / W(CO) = q CO /2q HI if n CR (HI)~n CR (H 2 ) –no virial equilibrium or gas/dust assumption, –but small bias from structured IC emission ← e - + far-IR field CloudR Gal (kpc) X in mol. cm -2 K -1 km -1 s Ophiuchus ± 0.2Local average at |b| > 5°: 1.61 ± 0.04 (>100 MeV) 1.73 ± 0.03 (>300 MeV) 1.8 ± 0.3 (I 100µ Dame ’01) Taurus ± 0.10 Cepheus ± 0.14Galactic average: 1.9 ± 0.2 ( Strong ’96) 1.56 ± 0.05 (Hunter ’97) Orion ± 0.15 Monoceros ± 0.31larger X in the outer Galaxy