Warm ISM in the Sgr A Complex. II. The [C/N] abundance ratio traced by
  [CII] 158 um and [NII] 205 um observations toward the Arched Filaments at the
  Galactic center
  Aims. We aim to investigate the I([CII]) versus I([NII]) integrated intensity
behavior in the AF region in order to assess the [CII] emission contribution
from the H II region, which is traced by [NII] line observations, and PDR
components in the high-metallicity environment of the GC. Methods. We used
[CII] 158 um and [NII] 205 um fine-structure line observations of the AF in the
literature to compare their observational integrated intensity distribution to
semi-theoretical predictions for the contribution of H II regions and adjacent
PDRs to the observed [CII] emission. We explored variations in the [C/N]
elemental abundance ratio to explain the overall behavior of the observed
relationship. Based on our models, the H II region and PDR contributions to the
observed [CII] emission is calculated for a few positions within and near to
the AF. Estimates for the [C/N] abundance ratio and [N/H] nitrogen elemental
abundance in the AF can then be derived. Results. The behavior of the I([CII])
versus I([NII]) relationship in the AF can be explained by model results
satisfying 0.84 < [C/N]_AF < 1.41, with model metallicities ranging from 1 Z to
2 Z, hydrogen volume density log n(H) = 3.5, and ionization parameters log U
from -1 to -2. A least-squares fit to the model data points yields log I([CII])
= 1.068log I([NII]) + 0.645 to predict the [CII] emission arising from the H II
regions in the AF. The fraction of the total observed [CII] emission arising
from within PDRs varies between ~ 0.20 and ~ 0.75. Our results yield average
values for the carbon-to-nitrogen ratio and nitrogen elemental abundances of
[C/N]_AF = 1.13 +/- 0.09 and [N/H]_AF = 6.21x10^4 for the AF, respectively.
They are a factor of ~ 0.4 smaller and ~ 7.5 larger than their corresponding
Galactic disk values.
