Detection of H_3+ in the Diffuse Interstellar Medium: The Galactic Center and Cygnus OB2 No. 12
T. R. Geballe(1), B. J. McCall(2), K. H. Hinkle(3,5), & T. Oka(4)
(1) Joint Astronomy Centre, Hilo, HI 96720
(2) Department of Astronomy and Astrophysics, Department of Chemistry, and the Enrico Fermi Institute, University of Chicago, Chicago, IL 60637
(3) National Optical Astronomy Observatories(1), Tucson, AZ 85726
(4) Department of Astronomy and Astrophysics, Department of Chemistry, and the Enrico Fermi Institute, University of Chicago, Chicago, IL 60637
(5) Operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation
Paper: accepted by ApJ
Abstract:
Absorption lines of H_3+ have been detected in the spectra of two
infrared sources in the galactic center and also towards the heavily
reddened star Cygnus OB2 No. 12, whose line of sight is believed to
include only diffuse interstellar gas. The absorptions toward the galactic
center sources (IRS3 and GCS3-2) probably are due to H_3+ both in
diffuse gas and in molecular clouds. The ratios of H_3+ line equivalent
width to extinction toward these three sources are much greater than those
toward dense clouds where H_3+ has been detected previously. Analysis of
the spectra coupled with a simple model for the abundance of H_3+ in the
diffuse interstellar medium implies that the observed H_3+ is present at
low densities along long pathlengths. These are the first detections of
H_3+ in the diffuse interstellar medium.
Preprints available from the authors at t.geballe@jach.hawaii.edu
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