Complex Molecules, Diffuse Clouds, Radio Frequencies

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Complex Molecules, Diffuse Clouds,Radio
Frequencies

• Harvey Liszt
• NRAO, CHARLOTTESVILLE
• Robert Lucas Jerome Pety
• IRAM, GRENOBLE

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• 13 years of mm-wave absorption line spec-troscopy
  (1992-2005) at IRAMs Plateau de Bure
  Interferometer
• Using 1 Jy compact extragalactic mm-wave
  continuum sources blazars of which there
  about 100 or so

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Like optical work except

• We look all the way out of the Galaxy, sometimes
  over very long sightlines
• Dark sightlines but diffuse clouds
• We resolve the line profiles (R3x106)
• Solves some problems with longer sightlines

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Like optical work except

• We see some same, some different species
• Optical H I, H2, H3 radio H I
• Optical OH, CO radio OH, CO, HCO, HOC
• Optical C2, C3, CN radio CN, HCN, HNC
• Optical CH, CH radio CH, C2H, C3H2
• Optical NH, N2 radio NH3
• Optical CS Radio CS, HCS, H2S, SO
• .. Radio H2CO

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RF Absorption Antecedents ca. 1992

• Dickey et al (1981) observations of OH in
  directions with H I absorption profiles
• Cox et al (1988) observations of C3H2
• Nash (1990) H2CO,NH3 toward B0355508
• Marscher, Bania, Wang (1991) mm-wave 12CO toward
  BL Lac (0.32 mag) at OVRO

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Serendipity, propinquity

• We began to study 13CO absorption at IRAM
• HCO absorption serendipitously seen toward BL
  Lac during calibration at PdB
• BL Lac flares
• We ask for time to observe other species, see
  C2H, HCN, HNC as well as HCO

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Reloaded
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How much HCO is there?

• N(HCO)/EB-V 3x1012 cm-2 mag-1
• N(HCO)/N(H2) 5x10-9 if fH20.2
• Fully ½ of OhishiIrvine (1992) value for TMC-1

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How much was there supposed to be?

• Conventional chemistry in diffuse gas
• C OH CO
• CO H2 HCO H sometimes
• CO H CO H (more)
• CO e C O (less)
• HCO e CO H
• gt HCO/OH 10-3, HCO/H2 10-10

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Diffuse Clouds Themes

• In absorption, otherwise hidden chemistry
  resembling that of dark gas
• In emission, CO both absent and faking the
  appearance of darker gas

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Issues

• Why so much H2 in the diffuse ISM?
• 25 40 of H-nuclei in H2 (?)
• Why such chemistry at low nH, AV ?
• extended CH problem for HCO, HCN, C2H, C3H2,
  H2CO, CS, H2S, usw.
• Where are the diffuse molecules?
• Well-mixed with H I? Separate? GMC? DMC?

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Click the sources
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Cygnus Beyond in E(B-V) CO
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A Bit Further Over Polaris Flare
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B0212735
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A quick breather

• Crater-like galactic geometry, HCO, EB-V
• Full HCO turn-on w/ H2, overabundant
• Free-floating HCO, C2H at EB-V 0.12
• Polyatomic absorption before CO emission
• HCN, SO, NH3, H2CO at EB-V 1/3
• Dark los, not dark gas

• Nil, normal large WCO/H2
• Strong CO emission from gas with CO/C ltlt 1
  (C/CO gtgt 1)
• 13CO fractionated, faking small CO/13CO
• High WCO sightlines lacking dark gas
• Large-scale CO surveys remain to be fleshed out

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And sulfur? CS, SO, H2 S HCS ( vs. HCO, HCN,
usw)click across the title to see some chemistry
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Click here for NH3
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Another breather

• Strong linear relationships in families
• OH HCO
• C2H C3H2
• CN, HCN HNC
• CS HCN, NH3 CS, H2CO
• Nonlinear relationships across families
• C2H, HCN, CS, H2CO, NH3 vs HCO

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Begin to exhale

• OH HCO trace H2 best (for us)
• Some species appear with the thinnest gas though
  not necessarily in fixed proportion
• OH HCO, C2H C3H2 , CO
• Others appear with higher N(HCO)
• CN, HCN, HNC
• CS, SO, H2S, HCS
• H2CO, NH3

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OH? Click title 4x then 2x in each box then on
OH last on diagram
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• But where can I read about all this work ???

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THE END

• Thanks for having me.
• When next you see a large-scale map of CO, think
  of me.
• If you visit the US, DONT EAT THE BEEF, we dont
  do much testing.
• And, please, be kind to radio astronomy