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Millimeter-wave Observations of Polyatomic Molecules in Diffuse Clouds

Published online by Cambridge University Press:  21 March 2006

Harvey Liszt ,
Robert Lucas  and
Jerome Pety
Harvey Liszt
Affiliation:
National Radio Astronomy Observatory, 520 Edgemont Road Charlottesville, VA 22903, USA
Robert Lucas
Affiliation:
Institut de Radioastronomie Millimétrique, 300 rue de la Piscine F38406 Saint Martin d'Hères, France
Jerome Pety
Affiliation:
Institut de Radioastronomie Millimétrique, 300 rue de la Piscine F38406 Saint Martin d'Hères, France Observatoire de Paris, 61 av. de l'Observatoire, F75014 Paris, France
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Abstract

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Millimeter-wave (mm-wave) absorption profiles toward extragalactic sources consistently find just diffuse (occasionally perhaps translucent) neutral gas—low/moderate density and extinction—along even some very long, dark lines of sight. CO, often heavily fractionated and mimicking the appearance of dark gas in emission, occasionally absent in emission even when present in absorption, is not the dominant form of carbon in these regions (presumably it is C+) yet the abundances of many other molecules resemble those seen in TMC-1. Some species (OH, HCO+, C2H and C3H2) turn on with high abundances just when H2 does; others (HCN, HNC, CN) require slightly higher $N$(H2) and yet others (CS and other sulfur-bearing species,NH3 and H2CO) even higher $N$(H2). The systematics and implications of these recent discoveries are discussed here.

Keywords

astrochemistry — ISM: clouds — ISM: molecules — ISM: structure
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 1 , Symposium S231: Astrochemistry: Recent Successes and Current Challenges , August 2005 , pp. 187 - 196
Copyright
2006 International Astronomical Union