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Extended Carbon Emission in the Galaxy: Dark Gas along the G328 Sightline

Part of: IAU Issue 315 - From Interstellar Clouds...

Published online by Cambridge University Press:  12 September 2016

M. Burton ,
M. Ashley ,
C. Braiding ,
M. Freeman ,
C. Kulesa ,
M. Wolfire ,
D. Hollenbach ,
G. Rowell  and
J. Lau
M. Burton
Affiliation:
School of Physics, University of New South Wales, Australia
M. Ashley
Affiliation:
School of Physics, University of New South Wales, Australia
C. Braiding
Affiliation:
School of Physics, University of New South Wales, Australia
M. Freeman
Affiliation:
School of Physics, University of New South Wales, Australia
C. Kulesa
Affiliation:
Steward Observatory, University of Arizona, USA
M. Wolfire
Affiliation:
Astronomy Department, University of Maryland, USA
D. Hollenbach
Affiliation:
Carl Sagan Center, SETI Institute, USA
G. Rowell
Affiliation:
School of Chemistry & Physics, University of Adelaide
J. Lau
Affiliation:
School of Chemistry & Physics, University of Adelaide
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Abstract

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We present spectral data cubes of the [CI] 809 GHz, 12CO 115 GHz, 13CO 110 GHz and HI 1.4 GHz line emission from a ~1° region along the l = 328° (G328) sightline in the Galactic Plane. The [CI] data comes from the High Elevation Antarctic Terahertz telescope at Ridge A on the summit of the Antarctic plateau, where the extremely low levels of precipitable water vapour open atmospheric windows for THz observations. The CO data comes from the Southern Galactic Plane Survey being conducted with the Mopra telescope. Emission arises principally from gas in three spiral arm crossings along the sight line. The distribution of the emission in the CO and [CI] lines is found to be similar, with the [CI] slightly more extended, and both are enveloped in extensive HI. Spectral line ratios are similar across the entire extent of the Galaxy. However, towards the edges of the molecular clouds the [CI]/13CO and 12CO/13CO line ratios rise by ~ 50%, and the [CI]/Hi ratio falls by ~ 10%. We attribute this to sightlines passing predominantly through the surfaces of photodissociation regions (PDRs), where the carbon is found mainly as C or C+ rather than CO, while the gas is mostly molecular. This is the signature of dark molecular gas.

Type
Poster Papers
Information
Proceedings of the International Astronomical Union , Volume 11 , Symposium S315: From Interstellar Clouds to Star-Forming Galaxies: Universal Processes? , August 2015 , E10
Copyright
Copyright © International Astronomical Union 2015 

References

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