Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoelectric Heating and [CII] Cooling of High Galactic Latitude
  Translucent Clouds   The (2P3/2 -> 2P1/2) transition of singly--ionized carbon, [CII], is the
primary coolant of diffuse interstellar gas. We describe observations of [CII]
emission towards nine high Galactic latitude translucent molecular clouds, made
with the long wavelength spectrometer on board the Infrared Space Observatory.
To understand the role of dust grains in processing the interstellar radiation
field (ISRF) and heating the gas, we compare the [CII] integrated intensity
with the far-infrared (FIR) integrated surface brightness for the 101 sampled
lines of sight. We find that [CII] is linearly correlated with FIR, and the
average ratio is equal to that measured with the COBE satellite for all
high-latitude Milky Way gas. There is a significant decrease that was not
detected with COBE in [CII] emissivity at high values of FIR. Our sample splits
naturally into two populations depending on the 60um/100um surface brightness
ratio, or color: ``warm'' positions and ``cold'' positions. A transition from
sources with warm to those with cold 60/100 colors coincides approximately with
the transition from constant to decreasing [CII] emissivity. We model the [CII]
and far-infrared emission under conditions of thermal equilibrium, using the
simplifying assumptions that, in all regions heated by the ISRF, the most
important source of gas heating is the photoelectric effect on grains and the
most important source of gas cooling is [CII] emission. The model matches the
data well. There are no statistically significant differences in the derived
values of the ISRF intensity and the photoelectric heating efficiency for warm
and cold sources. The observed variations in the [CII] emissivity and the
60/100 colors can be understood entirely in terms of the attenuation and
softening of the ISRF by translucent clouds, not changes in dust properties.

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The categories of this paper are: adap-org
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The categories of this paper are: math
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The categories of this paper are: cmp-lg
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
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The categories of this paper are: stat
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The categories of this paper are: cs
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The categories of this paper are: nlin
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The categories of this paper are: gr-qc
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-ex