J/AJ/169/291 12CO, 13CO, & C18O in Milky Way G24 region clouds (Yang+, 2025)
Distributions and physical properties of molecular clouds in the G24 region of
the Milky Way.
Yang T., Chen Xi, Xu X.-Y., Yang Y., Chen En, Li J., Ju B.-G., Lu D.-R.
<Astron. J., 169, 291 (2025)>
=2025AJ....169..291Y 2025AJ....169..291Y
ADC_Keywords: Molecular clouds; Galactic plane; Spectra, millimetric/submm;
Star Forming Region; Milky Way; Carbon monoxide; Molecular data
Keywords: Interstellar molecules ; CO line emission ; Molecular clouds ;
Star formation
Abstract:
We report the spatial distribution and physical characteristics of
molecular clouds in the G24 region, which is located near the
intersection of the Milky Way's Galactic bar with the Norma arm and
the 3kpc arm. Utilizing molecular line data from the Milky Way Imaging
Scroll Painting project, including 12CO, 13CO and C18O, along
with our own observations of the HCO+ line using the Purple Mountain
Observatory 13.7m telescope, we reveal the complex architecture of
molecular clouds in the G24 region. Seven giant molecular clouds, each
with a mass exceeding 104M☉ and a typical H2 column density
of 1021cm-2, have been identified through observations of CO and
its isotopes. The conversion factor XCO for the G24 region is
estimated to be 8.25x1019cm-2 (K.km/s)-1, aligning with the
typical values observed in other regions. Adopting the GaussClumps
algorithm, we identify a total of 257, 201, and 110 clumps in 12CO,
13CO and C18O within the G24 region, respectively. The derived
physical properties (including effective radius, mass, and virial
parameter) indicate that the majority of these clumps are
gravitationally bound, with a subset possessing the potential to form
massive stars. Examination of gas infall activities within these
clumps further suggests ongoing massive star formation. The complex
physical and kinematic environment, shaped by the G24 region's unique
location within the Milky Way, has limited the clear detection of gas
outflows.
Description:
The observations of CO and its isotopic molecules in the G24 region
were conducted as part of the Milky Way Imaging Scroll Painting
(MWISP) project, organized by the Purple Mountain Observatory (PMO).
The observations utilized the 13.7m telescope located in Delingha,
Qinghai Province, China, at an altitude of 3200m. The survey
simultaneously observed the J=1-0 transition of 12CO and its
isotopes 13CO and C18O. The first phase of the survey, covering an
area with Galactic longitudes l=[-10°,250°] and latitudes
b=[-5.2°,5.2°], ended in 2021 April after a decade-long
observation period. The second phase commenced in 2021 September,
expanding the survey's coverage to latitudes b=[-10°,10°],
with the anticipation that the survey will continue for another 10yr.
The front end uses a 3x3 beam sideband-separating superconducting
spectroscopic array receiver, and the back end comprises 18 fast
Fourier transform spectrometers (FFTSs). The upper sideband was used
to observe 12CO (115.271GHz), while the lower sideband was used to
record both 13CO (110.201GHz) and C18O (109.782GHz). Each FFTS has
a bandwidth of 1 GHz, with a velocity coverage of 2602km/s at
115.271GHz, 2722km/s at 110.201GHz, and 2732km/s at 109.782GHz.
Additionally, each FFTS has 16,384 channels, each of which has a width
of 61KHz and a corresponding velocity resolution of 0.159km/s for
12CO, 0.166km/s for 13CO, and 0.167km/s for C18O.
From 2022 May to June, we used the PMO 13.7m telescope to conduct OTF
mapping observations of the G24 region for the HCO+ (J=1-0; 89.2GHz)
transition. The FFTS, also with 1GHz bandwidth and 16,384 channels,
has a velocity coverage of 3364km/s at 89.2GHz, corresponding to a
velocity resolution of 0.205km/s for HCO+. The observation time is
more than 50hr.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 106 257 The parameters of 12CO clumps
tablea2.dat 108 201 The parameters of 13CO clumps
tablea3.dat 107 110 The parameters of C18O clumps
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See also:
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/A+A/527/A88 : Chemistry in infrared dark clouds (Vasyunina+, 2011)
J/MNRAS/443/1555 : ATLASGAL massive star forming clumps samp. (Urquhart+, 2014)
J/A+A/588/A104 : Molecular clouds and star formation (Gong+, 2016)
J/MNRAS/471/100 : Hi-GAL compact source catalog. -71.0<l<67.0 (Elia+, 2017)
J/ApJ/885/131 : ∼200 high-mass SFR plx & proper motion with VLBI (Reid+, 2019)
J/other/RAA/20.115 : Molecular clumps CO, HCO and HCN data (Yang+, 2020)
J/ApJS/252/20 : CO survey of the CMa OB1 complex (Lin+, 2021)
J/ApJS/254/3 : CO obs. of molecular clouds in the MW midplane (Ma+, 2021)
J/ApJS/268/1 : CO obs. of mol. clouds in the 3rd Gal. quadrant (Dong+, 2023)
J/AJ/167/228 : Physical properties of 221 clumps (Luo+, 2024)
J/AJ/168/52 : Infall motion in mol. clumps. V. HCO+ & HCN obs. (Yu+, 2024)
http://www.radioast.nsdc.cn/mwisp.php : Milky Way Imaging Scroll Painting
project website
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Num [1/257] Clump number (Number)
5- 9 A5 --- MWISP [MWISP] Source name prefix
11- 23 A13 --- Source Source name defined by Galactic
Coordinates (GDD.ddd+D.ddd)
25- 30 F6.2 km/s Vlsr [78.24/121.62] Central velocity
32- 35 F4.2 km/s dv [0.47/7.51] Linewidth (Delta_v)
37- 39 I3 arcsec MajAx [54/279] Major axis (theta_a)
41- 43 I3 arcsec MinAx [71/582] Minor axis (theta_b)
45- 47 I3 arcsec Diam [65/354] Diameter (theta_FWHM)
49- 51 I3 deg PA [-64/174] Position angle
53- 56 F4.2 kpc DistHC [5.01/7.66] Heliocentric distance
(Distance)
58- 61 F4.2 kpc DistGC [3.33/4.13] Galactocentric distance
(RGC)
63- 66 F4.1 K Tex [5.6/23.8] Excitation temperature
68- 71 F4.1 [cm-2] log(NH2) [20.4/21.7] Log of hydrogen column
density
73- 75 F3.1 pc Reff [0.6/6.4] Effective radius
77- 79 F3.1 [Msun] log(M) [1.7/4] Log of mass (log_Mclump)
81- 83 F3.1 [Msun] log(Mvir) [1.7/4.2] Log of virial mass
85- 88 F4.1 --- avir [0.7/12.1] Virial parameter (alpha_vir)
90- 92 F3.1 [Msun/pc2] log(Sig) [0.9/2.3] Log of surface density
(log_Sigma)
94- 96 F3.1 [cm-3] log(nH2) [0.6/3.1] Log of number density of
hydrogen molecules
98- 101 F4.2 km/s dvTh [0.1/0.2] Thermal linewidth (Delta_vth)
103- 106 F4.2 km/s dvNTh [0.45/7.51] Non-thermal linewidth
(Delta_vnth)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Num [1/201] Clump number (Number)
5- 9 A5 --- MWISP [MWISP] Source name prefix
11- 23 A13 --- Source Source name defined by Galactic
Coordinates (GDD.ddd+D.ddd)
25- 30 F6.2 km/s Vlsr [69.99/121.28] Central velocity
32- 35 F4.2 km/s dv [0.68/3.49] Linewidth (Delta_v)
37- 39 I3 arcsec MajAx [52/215] Major axis (theta_a)
41- 43 I3 arcsec MinAx [65/529] Minor axis (theta_b)
45- 47 I3 arcsec Diam [57/261] Diameter (theta_FWHM)
49- 51 I3 deg PA [-94/176] Position angle
53- 56 F4.2 kpc DistHC [5.02/7.49] Heliocentric distance
(Distance)
58- 61 F4.2 kpc DistGC [3.33/4.13] Galactocentric distance
(RGC)
63- 66 F4.1 K Tex [5/36.8] Excitation temperature
68- 71 F4.1 [cm-2] log(NH2) [20.4/22.2] Log of hydrogen column
density
73- 75 F3.1 pc Reff [0.4/5.6] Effective radius
77- 79 F3.1 [Msun] log(M) [1.7/4.3] Log of mass (log_Mclump)
81- 83 F3.1 [Msun] log(Mvir) [2.3/3.8] Log of virial mass
85- 88 F4.1 --- avir [0.1/12.6] Virial parameter (alpha_vir)
90- 92 F3.1 [Msun/pc2] log(Sig) [1/2.8] Log of surface density
(log_Sigma)
94- 96 F3.1 [cm-3] log(nH2) [2.3/4.4] Log of number density of
hydrogen molecules
98- 101 F4.2 km/s dvTh [0.09/0.24] Thermal linewidth
(Delta_vth)
103- 106 F4.2 km/s dvNTh [0.67/3.49] Non-thermal linewidth
(Delta_vnth)
108 A1 --- Flag Potential to form massive stars (*=Yes)
(Potential) (1)
--------------------------------------------------------------------------------
Note (1): Potential as follows:
* = Clumps have the potential to form massive stars (see Section 4.1.5);
8 occurrences
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Num [1/110] Clump number (Number)
5- 9 A5 --- MWISP [MWISP] Source name prefix
11- 23 A13 --- Source Source name defined by Galactic
Coordinates (GDD.ddd+D.ddd)
25- 30 F6.2 km/s Vlsr [79.67/121] Central velocity
32- 35 F4.2 km/s dv [0.34/2.63] Linewidth (Delta_v)
37- 39 I3 arcsec MajAx [51/130] Major axis (theta_a)
41- 43 I3 arcsec MinAx [63/220] Minor axis (theta_b)
45- 47 I3 arcsec Diam [58/134] Diameter (theta_FWHM)
49- 51 I3 deg PA [-44/157] Position angle
53- 56 F4.2 kpc DistHC [5.04/7.36] Heliocentric distance
(Distance)
58- 61 F4.2 kpc DistGC [3.33/4.11] Galactocentric distance
(RGC)
63- 66 F4.1 K Tex [4.8/21.8] Excitation temperature
68- 71 F4.1 [cm-2] log(NH2) [20.6/22.1] Log of hydrogen column
density
73- 75 F3.1 pc Reff [0.4/2.2] Effective radius
77- 79 F3.1 [Msun] log(M) [1.6/3.9] Log of mass (log_Mclump)
81- 83 F3.1 [Msun] log(Mvir) [1.3/3.4] Log of virial mass
85- 87 F3.1 --- avir [0.1/2.3] Virial parameter (alpha_vir)
89- 91 F3.1 [Msun/pc2] log(Sig) [1.4/2.8] Log of surface density
(log_Sigma)
93- 95 F3.1 [cm-3] log(nH2) [2.9/4.6] Log of number density of
hydrogen molecules
97- 100 F4.2 km/s dvTh [0.09/0.18] Thermal linewidth
(Delta_vth)
102- 105 F4.2 km/s dvNTh [0.3/2.63] Non-thermal linewidth
(Delta_vnth)
107 A1 --- Flag Potential to form massive stars (*=Yes)
(Potential) (1)
--------------------------------------------------------------------------------
Note (1): Potential as follows:
* = Clumps have the potential to form massive stars (see Section 4.1.5);
18 occurrences
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 23-Feb-2026