J/A+A/632/A60 CH 2THz spectra towards 7 molecular clouds (Jacob+, 2019)
Fingerprinting the effects of hyperfine structure on CH and OH far infrared
spectra using Wiener filter deconvolution.
Jacob A.M., Menten K.M., Wiesemeyer H., Lee M-Y., Guesten R., Duran C.A.
<Astron. Astrophys. 632, A60 (2019)>
=2019A&A...632A..60J 2019A&A...632A..60J (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Spectroscopy
Keywords: ISM: abundances - ISM: clouds - ISM: lines and bands -
ISM: molecules - method: data analysis
Abstract:
Despite being a commonly observed feature, the modification of the
velocity structure in spectral line profiles by hyperfine structure
complicates the interpretation of spectroscopic data. This is
particularly true for observations of simple molecules such as CH and
OH toward the inner Galaxy, which show a great deal of velocity
crowding.
In this paper, we investigate the influence of hyperfine splitting on
complex spectral lines, with the aim of evaluating canonical
abundances by decomposing their dependence on hyperfine structures.
This is achieved from first principles through deconvolution.
We present high spectral resolution observations of the rotational
ground state transitions of CH near 2THz seen in absorption toward the
strong FIR-continuum sources AGAL010.62-00.384, AGAL034.258+00.154,
AGAL327.293- 00.579, AGAL330.954-00.182, AGAL332.826-00.549,
AGAL351.581-00.352 and SgrB2(M). These were observed with the GREAT
instrument on board SOFIA. The observed line profiles of CH were
deconvolved from the imprint left by the lines' hyperfine structures
using the Wiener filter deconvolution, an optimised kernel acting on
direct deconvolution.
The quantitative analysis of the deconvolved spectra first entails the
computation of CH column densities. Reliable N(CH) values are of
importance owing to the status of CH as a powerful tracer for H2 in
the diffuse regions of the interstellar medium. The N(OH)/N(CH) column
density ratio is found to vary within an order of magnitude with
values ranging from one to 10, for the individual sources that are
located outside the Galactic centre. Using CH as a surrogate for H2,
we determined the abundance of the OH molecule to be X(OH)=1.09x10-7
with respect to H2. The radial distribution of CH column densities
along the sightlines probed in this study, excluding SgrB2(M),
showcase a dual peaked distribution peaking between 5 and 7 kpc. The
similarity between the correspondingly derived column density profile
of H2 with that of the CO-dark H2 gas traced by the cold neutral
medium component of [CII] 158um emission across the Galactic plane,
further emphasises the use of CH as a tracer for H2.
Description:
The observations were performed on several SOFIA flights in the
observatory's cycle 5 and 6 campaigns on 26 June and 6 July in 2017,
and 20 and 22 June in 2018.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 100 7 List of fits files
fits/* . 7 Individual fits files
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 33 A10 --- Obs.Date Observation date (YYYY-MM-DD)
35- 41 F7.4 km/s dVelo Velocity resolution
43- 45 F3.1 Kibyte size Size of FITS file
47- 66 A20 --- FileName Name of the FITS file in subdirectory fits
68-100 A33 --- Title Title of the FITS file
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Acknowledgements:
Arshia Maria Jacob, ajacob(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 04-Nov-2019