J/A+A/648/A38 J1717-3342 and J1744-3116 CO spectra (Gerin+, 2021)
CO+ as a probe of the origin of CO in diffuse interstellar clouds.
Gerin M., Liszt H.
<Astron. Astrophys. 648, A38 (2021)>
=2021A&A...648A..38G 2021A&A...648A..38G (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Radio lines ; Carbon monoxide ; Spectroscopy
Keywords: ISM: cloud - ISM: molecules - radio lines: ISM
Abstract:
The chemistry of the diffuse interstellar medium is driven by the
combined influences of cosmic rays, ultraviolet (UV) radiation, and
turbulence. Previously detected at the outer edges of
photodissociation regions (PDRs) and formed from the reaction of C+
and OH, CO+ is the main chemical precursor of HCO+ and CO in a
thermal, cosmic-ray, and UV-driven chemistry.
Our aim was to test whether the thermal cosmic-ray and UV-driven
chemistry is producing CO in diffuse interstellar molecular gas
through the intermediate formation of CO+ We searched for CO+
absorption with the Atacama Large Millimeter Array (ALMA) toward two
quasars with known Galactic foreground absorption from diffuse
interstellar gas, J1717-3342 and J1744-3116, targeting the two
strongest hyperfine components of the J=2-1 transition near 236GHz.
We could not detect CO+ but obtained sensitive upper limits toward
both targets. The derived upper limits on the CO+ column densities
represent about 4% of the HCO+ column densities. The corresponding
upper limit on the CO+ abundance relative to H2 is <1.2x10-10.
The non-detection of CO+ confirms that HCO+ is mainly produced in
the reaction between oxygen and carbon hydrides, CH2+ or CH3+,
induced by suprathermal processes, while CO+ and HOC+ result from
reactions of C+ with OH and H2O. The densities r equired to form
CO molecules at low extinction are consistent with this scheme.
Description:
Absorption spectra obtained with ALMA toward the quasars J1717-3342
and J1744-3116. The spectra are displayed as a function of rest
frequency and provided as FITS files. The spectra have been normalized
by the source continuum flux density. A flat baseline has been
subtracted to put the mean at zero.
The file name indicates the source and the targeted line. For each
source 4 files are provided, corresponding to the transitions
13CO(2-1), C18O(2-1), CO+ 2,3/2-1,1/2 and CO+ 2,5/2-1,3/2.
Objects:
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RA (2000) DE Designation(s)
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17 17 36.03 -33 42 08.8 PMN J1717-3342 = PKS 1714-336
17 44 23.58 -31 16 36.3 QSO J1744-3116 = PKS 1741-312
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 140 8 List of fits spectra
fits/* . 8 Individual fits spectra
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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 "date" Obs.Date Observation date
35- 46 E12.6 m/s bVELO-LSR Lower value of VELO-LSR interval
48- 58 E11.6 m/s BVELO-LSR Upper value of VELO-LSR interval
60- 66 F7.1 m/s dVELO-LSR VELO-LSR resolution
68- 74 F7.3 GHz Obs.Freq Observed frequency
76 I1 Kibyte size Size of FITS file
78-102 A25 --- FileName Name of FITS file, in subdirectory fits
104-140 A37 --- Title Title of the FITS file
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Acknowledgements:
Maryvonne Gerin, maryvonne.gerin(at)obspm.fr
(End) Patricia Vannier [CDS] 15-Feb-2021