J/A+A/642/A222 CS isotopes towards Galactic centre clouds (Humire+, 2020)
Sulphur and carbon isotopes towards Galactic centre clouds.
Humire P.K., Thiel V., Henkel C., Belloche A., Loison J.-C., Pillai T.,
Riquelme D., Wakelam V., Langer N., Hernandez-Gomez A., Mauersberger R.,
Menten K.M.
<Astron. Astrophys. 642, A222 (2020)>
=2020A&A...642A.222H 2020A&A...642A.222H (SIMBAD/NED BibCode)
ADC_Keywords: Galactic center ; Molecular clouds ; Radio lines ;
Interstellar medium
Keywords: Galaxy: centre - submillimetre: ISM - Galaxy: formation -
Galaxy: evolution - stars: atmospheres - submillimetre: general
Abstract:
Measuring isotopic ratios is a sensitive technique to obtain
information on stellar nucleosynthesis and chemical evolution.
We present measurements of the carbon and sulphur abundances in the
interstellar medium of the central region of our Galaxy. The selected
targets are the +50km/s Cloud and several line-of-sight clouds towards
Sgr B2(N).
Towards the +50km/s Cloud, we observed the J=2-1 rotational
transitions of 12C32S, 12C34S, 13C32S, 12C33S, and
13C34S, and the J=3-2 transitions of 12C32S and 12C34S
with the IRAM-30m telescope, as well as the J=6-5 transitions of
12C34S and 13C32S with the APEX 12m telescope, all in
emission. The J=2-1 rotational transitions of 12C32S,
12C34S, 13C32S, and 13C34S were observed with ALMA in Sgr
B2(N)'s envelope, with those of 12C32S and 12C34S also
observed in the line-of-sight clouds towards Sgr B2(N), all in
absorption.
In the +50km/s Cloud, we derive a 12C/13C isotopic ratio of
22.1+3.3-2.4, that leads, with the measured
13C32S/12C34S line intensity ratio, to a 32S/34S ratio of
16.3+3.0-2.4. We have also derived the 32S/34S isotopic ratio
more directly from the two isotopologues 13C32S and 13C34S,
which leads to an independent 32S/34S estimation of
16.3+2.1-1.7 and 17.9±5.0 for the +50km/s Cloud and Sgr B2(N),
respectively. We also obtain a 34S/33S ratio of 4.3±0.2 in the
+50km/s Cloud.
Previous studies observed a decreasing trend in the 32S/34S
isotopic ratios when approaching the Galactic centre. Our result
indicates a termination of this tendency at least at a galactocentric
distance of 130+60-30pc. This is at variance with findings based
on 12C/13C, 14N/15N and 18O/17O isotope ratios, where the
above-mentioned trend is observed to continue right to the central
molecular zone. This can indicate a drop in the production of massive
stars at the Galactic centre, in the same line as recent metallicity
gradient ([Fe/H]) studies, and opens the work towards a comparison
with Galactic and stellar evolution models.
Description:
Spectra of the above mentioned species are presented. The data were
obtained with the APEX, ALMA and IRAM 30m telescopes. Spectra from
ALMA and IRAM are in ascii format, either in frequency (with an
extension: "_f" in the name) or in velocity. This data is the same
that the one presented in Table 1 of the paper.
All spectra were smoothed to a common resolution of 3km/s.
ALMA data (Sgr B2(N)) is divided by their offset position as described
in Table 4 and labelled in Figure 1 of the paper. The offset positions
with respect to the centre of the observed field
(17:47:19.87, -28:22:16 (J2000)), in units of arcseconds, are:
(1.8, 11.1), (9.3, 1.8), (4.8,9.3) and (6.6, 3.3), corresponding to
K4, K6_shell, K5_shell and K6_shell,a, in Fig. 1, respectively.
Objects:
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RA (2000) DE Designation(s)
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17 45 50.20 -28 59 41.1 50 Cloud = [IKP2016] 50 km s-1 cloud
17 47 19.87 -28 22 16 Sgr B2(N) = NAME Sgr B2 (North)
-------------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 101 38 List of spectra
50cloudf/* . 9 Individual 50 Cloud Frequency/Tmb spectra
50cloudv/* . 9 Individual 50 Cloud velocity/Tmb spectra
sgrb2_n/* . 4 Individual SgrB2 N GILDAS spectra
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 43 A43 --- FileName Name of the spectrum file
45-101 A57 --- Title Title of the file (1)
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Note (1): The +50 km/s Cloud (50 Cloud) could include additional molecular knots
on its positive-longitude side (Ferriere, 2012A&A...540A..50F 2012A&A...540A..50F)
Subdirectory for Sgr B2(N) data indicating position offset with respect to the
central observed position: EQ J2000:17:47:19.87,-28:22:16.
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Byte-by-byte Description of file: 50cloudf/*
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Bytes Format Units Label Explanations
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1- 17 E17.12 MHz Freq Observed frequency
18- 38 E21.16 K Tmb temperature main beam
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Byte-by-byte Description of file: 50cloudv/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 20 F20.15 km/s Vel Observed velocity
22- 41 E20.15 K Tmb Temperature main beam
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Acknowledgements:
Pedro K. Humire, phumire(at)mpifr-bonn.mpg.de
(End) Pedro Humire [SSDOO/ADC], Patricia Vannier [CDS] 02-Sep-2020