J/ApJ/877/154 H2CO TMRT obs. of Galactic molecular clouds (Yan+, 2019)
A systematic TMRT observational study of Galactic 12C/13C ratios from
formaldehyde.
Yan Y.T., Zhang J.S., Henkel C., Mufakharov T., Jia L.W., Tang X.D.,
Wu Y.J., Li J., Zeng Z.A., Wang Y.X., Li Y.Q., Huang J., Jian J.M.
<Astrophys. J., 877, 154 (2019)>
=2019ApJ...877..154Y 2019ApJ...877..154Y
ADC_Keywords: Molecular clouds; Interstellar medium; Radio lines
Keywords: Galaxy: evolution ; HII regions ; ISM: abundances
Abstract:
We present observations of the C-band 110-111 (4.8GHz) and Ku-band
211-212 (14.5GHz) K-doublet lines of H2CO and the C-band
110-111 (4.6GHz) line of H213CO toward a large sample of
Galactic molecular clouds, through the Shanghai Tianma 65m radio
telescope (TMRT). Our sample with 112 sources includes strong H2CO
sources from the TMRT molecular line survey at C-band and other known
H2CO sources. All three lines are detected toward 38 objects
(43 radial velocity components) yielding a detection rate of 34%.
Complementary observations of their continuum emission at both C- and
Ku-bands were performed. Combining spectral line parameters and
continuum data, we calculate the column densities, the optical depths
and the isotope ratio H212CO/H213CO for each source. To
evaluate photon trapping caused by sometimes significant opacities in
the main isotopologue's rotational mm-wave lines connecting our
measured K-doublets, and to obtain 12C/13C abundance ratios, we
used the RADEX non-LTE model accounting for radiative transfer
effects. This implied the use of the new collision rates from
Wiesenfeld & Faure. Also implementing distance values from
trigonometric parallax measurements for our sources, we obtain a
linear fit of 12C/13C=(5.08±1.10)DGC+(11.86±6.60), with a
correlation coefficient of 0.58. DGC refers to Galactocentric
distances. Our 12C/13C ratios agree very well with the ones
deduced from CN and C18O but are lower than those previously
reported on the basis of H2CO, tending to suggest that the bulk of
the H2CO in our sources was formed on dust grain mantles and not in
the gas phase.
Description:
The 110-111 and 211-212 transitions were observed toward our
sources in 2016 March and October as well as in 2017 May and July with
the Shanghai Tianma Radio Telescope (TMRT). We used two cryogenically
cooled receivers covering the frequency ranges of 4.0-8.0GHz (C-band)
and 12.0-18.2GHz (Ku-band). The rest frequencies of the 110-111
transitions of H212CO and H213CO were set to be 4.829660 and
4.593089GHz, respectively.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 74 262 H212CO and H213CO 110-111 observations
of the entire sample
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See also:
VI/51 : Collisional Excitation Rates of Formaldehyde (Green 1991)
J/A+A/361/1079 : HNCO in massive galactic dense cores (Zinchenko, 2000)
J/ApJS/138/63 : H2CO and Hα observations of UC HII (Araya+, 2002)
J/ApJ/587/714 : H2CO and Hα observations of UC HII (Watson+, 2003)
J/ApJS/154/553 : Inner galaxy massive star formation regions (Sewilo+, 2004)
J/ApJ/699/1153 : Distances to GRS molecular clouds (Roman-Duval+, 2009)
J/A+A/493/687 : Rotational excitation of formaldehyde by H2 (Faure+, 2009)
J/ApJ/723/915 : Aquila star-forming region with BLAST (Rivera-Ingraham+, 2010)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/A+A/598/A30 : Massive star forming molecular clumps Tkin (Tang+, 2017)
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Source Name
15- 15 A1 --- f_Name Flag on Name (1)
17- 18 I2 h RAh Hour of Right Ascension (J2000)
20- 21 I2 min RAm Minute of Right Ascension (J2000)
23- 27 F5.2 s RAs Second of Right Ascension (J2000)
29- 29 A1 --- DE- Sign of the Declination (J2000)
30- 31 I2 deg DEd Degree of Declination (J2000)
33- 34 I2 arcmin DEm Arcminute of Declination (J2000)
36- 40 F5.2 arcsec DEs Arcsecond of Declination (J2000)
42- 56 A15 --- Line Molecular species (2)
58- 62 F5.1 min Texp [2/438] Integration time, minutes (3)
64- 68 F5.1 mK rms [4.3/186] RMS noise obtained from Gaussian fitting
70- 74 F5.3 km/s DV [0.059/0.84] Corresponding channel width
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Note (1): Source flags as follows:
a = The sources only detected in the 110-111 lines of H212CO;
b = The sources not detected in both the 110-111 lines of H212CO
and H213CO.
Note (2): (C) and (Ku) indicate the C- (4-8GHz) and Ku-band (12-18.2GHz),
respectively.
Note (3): The integration time is ON-source + OFF-source.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 24-Nov-2020