paper

Deficit of Far-Infrared [CII] Line Emission toward the Galactic Center

arXiv:astro-ph/9510002 · doi:10.1086/309810

Abstract

We have observed the [CII] 158 micron line emission from the Galactic plane (-10 deg < l < 25 deg, |b| <= 3 deg) with the Balloon-borne Infrared Carbon Explorer (BICE). The observed longitudinal distribution of the [CII] line emission is clearly different from that of the far-infrared continuum emission; the Galactic center is not the dominant peak in the [CII] emission. Indeed, the ratio of the [CII] line emission to far-infrared continuum (I_[CII] / I_FIR) is systematically low within the central several hundred parsecs of the Galaxy. The observational results indicate that the abundance of the C+ ions themselves is low in the Galactic center. We attribute this low abundance mainly to soft UV radiation with fewer C-ionizing photons. This soft radiation field, together with the pervasively high molecular gas density, makes the molecular self-shielding more effective in the Galactic center. The self-shielding further reduces the abundance of C+ ions, and raises the temperature of molecular gas at the C+/C/CO transition zone.

arXiv commentCompressed uuencoded postcript, 15 pages with 2 figures, to appear in the Astrophysical Journal (Letters)

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