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Paper: The Motion and Distribution of Warm Diffuse Gas in the Central Molecular Zone as Revealed by Spectra of H3+
Volume: 528, New Horizons in Galactic Center Astronomy and Beyond
Page: 45
Authors: Geballe, T. R.
Abstract: Spectra of absorption lines of H3+ across the Central Molecular Zone (CMZ) of the Galaxy show that a previously little observed component of the interstellar medium there, warm (T ∼ 200 K) and diffuse (n ∼ 50 cm–3) gas, inhabits a large fraction of the volume of the front half of the CMZ, and that this gas is moving radially outwards from the center. It is likely that gas with similar properties also takes up much of the rear half of the CMZ. The spectra rule out hot X-ray-emitting plasma filling the majority of the volume of the CMZ, are consistent with sub-millimeter and millimeter data indicating that the filling factor of dense (n ≳ 104 cm–3) molecular gas is far less than the originally suggested value of ≳ 0.1, physically link the diffuse expanding gas within the CMZ to the Expanding Molecular Ring (EMR) of gas at the periphery of the CMZ, are inconsistent with orbital motion of the diffuse gas, and imply a high H2 cosmic-ray ionization rate of ∼2 × 10–14 s-1.
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