J/A+A/610/A10 Sgr B2 los molecular absorption line spectra (Corby+, 2018)
The molecular chemistry of diffuse and translucent clouds in the line-of-sight
to Sgr B2: Absorption by simple organic and inorganic molecules in the GBT
PRIMOS survey.
Corby J.F., McGuire B.A., Herbst E., Remijan A.J.
<Astron. Astrophys. 610, A10 (2018)>
=2018A&A...610A..10C 2018A&A...610A..10C (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Interstellar medium ; Spectroscopy
Keywords: astrochemistry - radio lines: ISM - ISM: abundances -
molecular processes - ISM: structure - Galaxy: center
Abstract:
The 1-50 GHz PRebiotic Interstellar MOlecular Survey (PRIMOS) contains
>50 molecular absorption lines observed in clouds located in the
line-of-sight to Sgr B2(N). The line-of- sight material is associated
with diffuse and translucent clouds located in the Galactic Center,
Bar, and spiral arms in the disk. We measure the column densities and
estimate abundances, relative to H2, of 11 molecules and additional
isotopologues observed in this material. We use absorption by
optically thin transitions of c-C3H2 to estimate the molecular
hydrogen columns, and argue that this method is preferable to more
commonly used methods. We discuss the kinematic structure and
abundance patterns of small molecules including the sulfur-bearing
species CS, SO, CCS, H2CS, and HCS+; oxygen-bearing molecules OH,
SiO, and H2CO; and simple hydrocarbon molecules c-C3H2, l-C3H,
and l-C3H+. Finally, we discuss the implications of the observed
chemistry for the structure of the gas and dust in the ISM.
Highlighted results include the following. First, whereas gas in the
disk has a molecular hydrogen fraction of 0.65, clouds on the outer
edge of the Galactic Bar and in or near the Galactic Center have
molecular fractions of 0.85 and >0.9, respectively. Second, we observe
trends in isotope ratios with Galactocentric distance; while carbon
and silicon show enhancement of the rare isotopes at low
Galactocentric distances, sulfur exhibits no trend with Galactocentric
distance. We also determine that the ratio of c-C3H2/c-H13CCCH
provides a good estimate of the 12C/13C ratio, whereas
H2CO/H2(13C)O exhibits fractionation. Third, we report the
presence of l-C3H+ in diffuse clouds for the first time. Finally,
we suggest that CS has an enhanced abundance within higher density
clumps of material in the disk, and therefore may be diagnostic of
cloud conditions. If this holds, the diffuse clouds in the Galactic
disk contain multiple embedded hyperdensities in a clumpy structure,
and the density profile is not a simple function of AV.
Description:
Spectra covering transitions of c-C3H2, c-H13CCCH, CS, C34S,
SO, CCS, H2CS, HCS+, OH, SiO, 29SiO, H2CO, H2(13C)O,
l-C3H, and l-C3H+ with line-of-sight absorption observed in the
1-50 GHz data from the PRebiotic Interstellar MOlecular Survey
(PRIMOS) taken with the Robert C. Byrd Green Bank Telescope (GBT).
Data were observed between 2001 and 2014, with the majority of the
data obtained in 2007 in GBT Key Science project ID GBT07A-051.
Spectra have been baseline-subtracted using best fit polynomials as
described in the paper, and normalized by the continuum, so that the
y-axis represents (T/TC-1). Data are provided in the FITS format;
each FITS file contains all lines of a single molecule that are
observed to have foreground absorption. Please refer to Table 1 of the
paper to obtain molecular transition rest frequencies, energies, GBT
beam sizes, and transition quantum numbers.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
17 47 20.4 -28 22 12 Sgr B2 = NAME SGR B2
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
spectra.dat 83 26 list of spectra
fits/* . 15 Individual fits files
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See also:
J/MNRAS/452/3969 : ATCA Survey of Sagittarius B2 at 7mm (Corby+, 2015)
J/A+A/559/A47 : Sgr B2(N) and Sgr B2(M) IRAM 30m line survey
(Belloche+, 2013)
Byte-by-byte Description of file: spectra.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 8 F8.4 deg RAdeg Right Ascension of center (J2000)
10- 17 F8.4 deg DEdeg Declination of center (J2000)
19 I1 --- Nrec [1/4] Number of records in the fits file
21- 24 I4 --- Nline Number of lines
26- 43 A18 --- FileName Name of FITS file, in subdirectory fits
45-110 A66 --- Title Descriptor of file contents
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Acknowledgements:
Joanna Corby, jfc2113(at)gmail.com
Anthony Remijan, aremijan(at)nrao.edu
National Radio Astronomy Observatory
Funding through University of Virginia, Eric Herbst
References:
Thiel et al., 2017A&A...605L...6T 2017A&A...605L...6T, Complex organic molecules in diffuse
clouds along the line of sight to Sagittarius B2.
(End) Patricia Vannier [CDS] 15-Dec-2017