J/ApJS/219/28 C18O/C17O ratios in the Galactic center (Zhang+, 2015)
Isotopic ratios of 18O/17O in the Galactic central region.
Zhang J.S., Sun L.L., Riquelme D., Henkel C., Lu D.R., Zhang Y., Wang J.Z.,
Wang M., Li J.
<Astrophys. J. Suppl. Ser., 219, 28 (2015)>
=2015ApJS..219...28Z 2015ApJS..219...28Z (SIMBAD/NED BibCode)
ADC_Keywords: Radio lines ; Interstellar medium ; Milky Way
Keywords: Galaxy: center; ISM: abundances; ISM: molecules; radio lines: ISM
Abstract:
The 18O/17O isotopic ratio of oxygen is a crucial measure of the
secular enrichment of the interstellar medium by ejecta from high-mass
versus intermediate-mass stars. So far, however, there is a lack of
data, particularly from the Galactic center (GC) region. Therefore, we
have mapped typical molecular clouds in this region in the J=1-0 lines
of C18O and C17O with the Delingha 13.7m telescope (DLH).
Complementary pointed observations toward selected positions
throughout the GC region were obtained with the IRAM 30m and Mopra 22m
telescopes. C18O/C17O abundance ratios reflecting the 18O/17O
isotope ratios were obtained from integrated intensity ratios of
C18O and C17O. For the first time, C18O/C17O abundance ratios
are determined for Sgr C (V~-58km/s), Sgr D (V∼80km/s), and the
1.3° complex (V∼80km/s). Through our mapping observations,
abundance ratios are also obtained for Sgr A (∼0 and ∼50km/s
component) and Sgr B2 (∼60km/s), which are consistent with the results
from previous single-point observations. Our frequency-corrected
abundance ratios of the GC clouds range from 2.58±0.07 (Sgr D,
V∼80km/s, DLH) to 3.54±0.12 (Sgr A, ∼50km/s). In addition, strong
narrow components (line width less than 5km/s) from the foreground
clouds are detected toward Sgr D (-18km/s), the 1.3° complex
(-18km/s), and M+5.3-0.3 (22km/s), with a larger abundance ratio
around 4.0. Our results show a clear trend of lower C18O/C17O
abundance ratios toward the GC region relative to molecular clouds in
the Galactic disk. Furthermore, even inside the GC region, ratios
appear not to be uniform. The low GC values are consistent with an
inside-out formation scenario for our Galaxy.
Description:
Our mapping observations of the J=1-0 lines of 12CO, 13CO, C18O,
and C17O were carried out with the DLH 13.7m telescope of the Purple
Mountain Observatory (PMO) at Delingha in 2011 January and 2012 May
and November.
The C18O and C17O lines were also observed in single-point mode
toward Sgr B2 with the IRAM 30m telescope in 2011 September, and
toward Sgr C and Sgr D with the Mopra 22m in 2014 June.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 92 12 Measured values of 18O/17O
table3.dat 55 202 Integrated intensities and relative abundance ratios
of the mapped regions
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See also:
J/A+A/559/A47 : Sgr B2(N) and Sgr B2(M) IRAM 30m line survey (Belloche+, 2013)
J/PASJ/62/557 : CO clouds in the Galactic Center from NANTEN (Takeuchi+, 2010)
J/A+A/430/549 : C18O/C17O near rho Oph (Wouterloot+, 2005)
J/ApJS/117/427 : Sgr B2 spectral survey (Nummelin+, 1998)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Reg Region identifier
11 A1 --- Inst Instrument (1)
13- 18 F6.3 deg GLON [-0.6/5.5]? Galactic longitude
20- 25 F6.3 deg GLAT [-0.4/0.07]? Galactic latitude
27 A1 --- u_V18c [~] Uncertainty flag on V18c
28- 30 I3 km/s V18c C18O velocity (or lower range)
32- 33 I2 km/s V18c2 [80]? upper range of V18c
35 A1 --- u_W18c [~] Uncertainty flag on W18c
36- 39 F4.1 km/s W18c Line width of the C18O J=1-0 (or lower range)
41- 42 I2 km/s W18c2 [30/50]? Upper range of W18c
44 A1 --- u_V17c [~] Uncertainty flag on V17c
45- 47 I3 km/s V17c C17O velocity (or lower range)
49- 50 I2 km/s V17c2 [80]? Upper range of V17c
52 A1 --- u_W17c [~] Uncertainty flag on W17c
53- 56 F4.1 km/s W17c Line width of the C17O J=1-0 (or lower range)
58- 59 I2 km/s W17c2 [30/50]? Upper range of W17c
61- 62 I2 --- N [7/58]? Numbers of positions in each map (2)
64- 67 F4.2 --- C18/C17a [2.4/3.7]? Integrated intensity ratio
C18O/C17O (3)
69- 72 F4.2 --- e_C18/C17a [0.1/0.5]? C18/C17a uncertainty
74- 77 F4.2 --- C18/C17m [2.4/4.7]? Mean C18O/C17O ratio (4)
79- 82 F4.2 --- e_C18/C17m [0.07/0.2]? C18/C17m uncertainty
84- 87 F4.2 --- Rcor [2.5/4.9] Frequency-corrected abundance ratios
were deduced from those mean values (5)
89- 92 F4.2 --- e_Rcor [0.08/0.6] Uncertainty on Rcor
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Note (1): Instrument code as follows:
I = IRAM 30m
M = Mopra 22m
Note (2): Numbers of positions in each map, which match our criteria,
i.e., C18O and C17O lines show the same velocity component and
exhibit sufficient (>5σ) S/N.
Note (3): C18/C17a uncertainty the C18O and C17O spectra of each map.
Note (4): deduced from the C18O/C17O ratios of individual positions.
Note (5): Results from our single-point observations with IRAM 30m and
Mopra 22m are also presented.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Reg Region identifier (1)
9- 11 I3 km/s Vel [-18/80]? Approximate component velocity
of the region
13- 17 F5.2 arcmin oGLON Galactic longitude offset (2)
19- 23 F5.2 arcmin oGLAT Galactic latitude offset (2)
25- 29 F5.2 K.km/s C18O [5.8/54.2] Integrated C18O intensity
31- 34 F4.2 K.km/s e_C18O [0.3/3.5] Standard deviation in C18O
36- 40 F5.2 K.km/s C17O [1.1/21.5] Integrated C17O intensity
42- 45 F4.2 K.km/s e_C17O [0.1/1.5] Standard deviation in C17O
47- 50 F4.2 --- Ratio [1.7/5.8] Integrated C18O/C17O intensity
ratio
52- 55 F4.2 --- e_Ratio [0.1/1.6] Standard deviation in Ratio
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Note (1): "1.3 deg" is the 1.3° complex.
Note (2): Relative to (0,0) position of the mapped region where l,b for the
individual regions are:
GLON , GLAT
Sgr A = ~-0.052, ~-0.046;
SgrB2 = ∼ 0.68 , ~-0.06;
SgrC = -0.554, -0.124;
SgrD = 1.131, -0.107;
1.3 deg complex = 1.28 , 0.07.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-Sep-2015