J/AJ/170/239 MWISP molecular clouds parameters from 12CO emission (Zhou+, 2025)
Molecular gas distribution toward the inner and outer Galaxy revealed by MWISP-
The galactic longitude 45°-60° and 120°-130°.
Zhou X., Yang Ji, Sun Y., Yan Q.-Z., Yuan L., Su Y., Chen X., Zhang S.
<Astron. J., 170, 239 (2025)>
=2025AJ....170..239Z 2025AJ....170..239Z
ADC_Keywords: Molecular clouds; Interstellar medium; Radio lines; Milky Way;
Millimetric/submm sources; Carbon monoxide; Space velocities;
Velocity dispersion; Spectra, radio
Keywords: Interstellar medium ; Molecular clouds ; Galaxy structure ;
Radio astronomy
Abstract:
Molecular clouds (MCs) are cradles of star and planet formation,
thereby playing an important role in the evolution of galaxies. Based
on the unbiased Milky Way Imaging Scroll Painting survey data of 12CO,
13CO, and C18O (J=1-0) line emission in two regions toward the
inner and outer Galaxy, i.e., the G50 (44.75°≤l≤60.25°) and
G120 (119.75°≤l≤130.25°) regions, the distribution of
molecular gas is studied. Both regions have Galactic latitudes of
|b|≤5.25°. A catalog containing 24,724 MCs is constructed from
the data. In our proximity, several molecular structures with large
angular scales and small velocity dispersions are discovered,
resembling curtains of mist. Beyond the nearby molecular gas, a clear
aggregation of MCs along coherent structures in the Galactic plane is
visible, sketching spiral arm structures. Nevertheless, the
aggregation of MCs is also detected in the inter-arm region between
the Perseus and Outer arms in the G50 region. The Galactic molecular
disk in this inter-arm region is found to be thinner than that in the
adjacent spiral arm region. In addition, the thickness of the Galactic
molecular disk examined here is found to be correlated with the warp
of it, indicating their homologous origins. The molecular disk has a
typical thickness of ∼220pc in the inner Galaxy. Moreover, the
dispersion of the MC systemic velocity decreases with increasing
galactocentric radius, resulting in lower kinematic distance
uncertainties at larger radii. However, the Perseus arm segment in the
G120 region exhibits a relatively large cloud-to-cloud velocity
dispersion and split components in its MC velocity distribution.
Description:
The CO line emission was observed using the Purple Mountain
Observatory (PMO) 13.7m millimeter-wavelength telescope located in
Delingha, China, as part of the Milky Way Imaging Scroll Painting
(MWISP) project (see Su+, 2019ApJS..240....9S 2019ApJS..240....9S; Sun+, 2020ApJS..246....7S 2020ApJS..246....7S).
We mapped two regions toward the inner and outer Galaxy, namely the
G50 (44.75°≤l≤60.25°) and G120 (119.75°≤l≤130.25°)
regions, both with the Galactic latitude |b|≤5.25°.
The 12CO (J=1-0), 13CO (J=1-0), and C18O (J=1-0) lines were
observed simultaneously by the 3x3 multibeam sideband separation
receiver, i.e., the Superconducting Spectroscopic Array Receiver.
The final sample built here for the G120 and G50 regions contains
24,724 MCs. In the sample, 276 MCs extend to the boundary of the
observation coverage and are excluded from the analysis in the paper.
Additionally, there are 4171 MCs not fully resolved, i.e., with a
longitude or latitude span of two pixels.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 109 24724 Basic parameters derived by 12CO (J=1-0) emission
for all MCs
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See also:
VII/7A : Lynds' Catalogue of Dark Nebulae (LDN) (Lynds 1962)
VII/114 : Massachusetts-Stony Brook Galactic Plane CO Survey (Clemens+ 1986)
J/A+AS/25/25 : HII regions of the Northern Milky Way (Dubout-Crillon+ 1976)
J/A+A/275/67 : Velocity Field of the outer Galaxy (Brand+ 1993)
J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)
J/A+A/383/631 : Catalogue of dust clouds in the Galaxy (Dutra+, 2002)
J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008)
J/ApJS/185/198 : The Cepheus flare observed with IRAC and MIPS (Kirk+, 2009)
J/ApJS/182/131 : Molecular clouds and clumps in the GRS (Rathborne+, 2009)
J/ApJ/699/1153 : Kinematic dist. to GRS molecular clouds (Roman-Duval+, 2009)
J/ApJ/723/492 : Phys. properties of GRS molecular clouds (Roman-Duval+, 2010)
J/ApJ/798/L27 : CO obs. of molecular clouds in the 2nd quadrant (Sun+, 2015)
J/ApJ/828/59 : Molecular clouds in the Milky Way with CO obs. (Su+, 2016)
J/A+A/594/A28 : Planck Cat. of Galactic cold clumps (PGCC) (Planck+, 2016)
J/A+A/601/A124 : Clouds in SEDIGISM sci. demonstration field (Schuller+, 2017)
J/ApJS/230/17 : CO obs. of MCs in the Extreme Outer Galaxy region (Sun+, 2017)
J/other/NatAs/3.320 : Galactic classical Cepheids catalog (Chen+, 2019)
J/MNRAS/483/4291 : Properties of JCMT CO(3-2) molecular clouds (Colombo+, 2019)
J/ApJ/885/131 : ∼200 high-mass SFR plx & proper motion with VLBI (Reid+, 2019)
J/A+A/632/A58 : Physical properties of CHIMPS clumps (Rigby+, 2019)
J/MNRAS/500/3027 : The SEDIGISM survey: molecular clouds (Duarte-Cabral+, 2021)
J/MNRAS/500/3064 : The SEDIGISM survey: First Data Release (Schuller+, 2021)
J/ApJ/910/131 : Molecular gas distribution from MWISP CO survey (Su+, 2021)
J/ApJS/257/51 : Morphological classif. of MWISP 12CO mol. cl. (Yuan+, 2021)
J/ApJS/261/37 : 13CO emission in MWISP 12CO molecular clouds (Yuan+, 2022)
J/ApJS/262/5 : A CO survey of the entire northern sky (Dame+, 2022)
J/A+A/663/A56 : SEDIGISM: Molecular Cloud morphology I. (Neralwar+, 2022)
J/ApJS/268/61 : Associations between SNRs & molecular clouds (Zhou+, 2023)
J/AJ/167/220 : 207 molecular clouds dist. measurements; MWISP (Zhang+, 2024)
J/ApJS/275/35 : CO molecular clouds from the MWISP project (Sun+, 2024)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Cloud Cloud identifier, MWISP GLLL.lll+BBB.bbb
23 A1 --- Flag *=Clouds with incomplete coverage (1)
25- 31 F7.3 deg GLON [44.75/130.25] Intensity-weighted mean
Galactic longitude, 12CO(1-0) line
33- 38 F6.3 deg GLAT [-5.25/5.25] Intensity-weighted mean Galactic
latitude, 12CO(1-0) line
40- 45 F6.1 km/s Vsys [-110.1/96.9] Intensity-weighted mean LSR
velocity (2)
47- 50 F4.2 km/s sigma [0.31/3.6] Velocity dispersion (3)
52- 56 F5.2 K.km/s W [0.27/22] Average integrated intensity
58- 65 F8.1 arcmin2 A [0.8/165491.5] Angular area of the cloud,
square arcminutes
67- 73 E7.1 cm-2 NH2 [5.9e+19/4e+21] H2 column density (4)
75- 78 F4.1 kpc Dist [0.2/19.2]? Kinematic distance (5)
80- 83 F4.1 kpc Rgal [5.7/19.8]? Distance to the Galactic center (6)
85- 92 F8.3 pc Zgal [-900/1300]? Height from the Galactic plane (7)
94- 101 F8.4 pc Rad [8.8e-3/260]? Cloud radius (8)
103- 109 E7.1 Msun Mass [5.7e-3/2.3e7]? Cloud mass (9)
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Note (1): Clouds with incomplete coverage, i.e. extending to the
boundary of the observation coverage.
Note (2): Intensity-weighted, Local Standard of Rest (LSR) mean velocity of
13CO (J=1-0) emission; if no significant 13CO (J=1-0) emission is
detected, that of 12CO (J=1-0) emission is applied instead.
Note (3): Velocity dispersion, derived as the square root of the
intensity-weighted velocity variance (moment II).
Note (4): Estimated using the conversion factor
N(H2)/W(12CO)=1.8e+20cm-2.(K.km/s)-1, Dame+ (2001ApJ...547..792D 2001ApJ...547..792D).
Note (5): Estimated based on the systemic velocity, Section 3.3
Note (6): Distance to the Galactic center, derived as
Rgal=sqrt(D2.cos2(b)+R20,gal-2.D.R0,gal.cos(b).cos(l)), where
R0,gal=8.15kpc is the Sun's distance to the Galactic center
(Reid+2019, J/ApJ/885/131).
Note (7): Height from the Galactic plane, corrected by the Sun's
height above the Galactic midplane as 15.7pc (Zhou+2023, J/ApJS/268/61;
Su+, 2019ApJS..240....9S 2019ApJS..240....9S).
Note (8): Cloud radius, derived as the average of the half widths at
half maximum (HWHM) along the projected minor and major axes. The
HWHM of the axes are estimated by the intensity-weighted second
moment around the center and converted to HWHM by multiplying by
1.1774. The lengths of the axes are deconvolved from the beam to
correct for the finite angular resolution, so the corresponding
radius is corrected as well. For MCs with spatial extensions in
the l or b directions equal to two pixels (i.e. not fully
resolved), no radius value is given (null, blank).
Note (9): Cloud mass, estimated as M=N(H2).A.Dist2.µ(H2).mH, where
µ(H2)=2.8 is the average molecular weight per hydrogen molecule
(Kauffmann+2008, J/A+A/487/993), and mH is the hydrogen atom mass.
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 23-Jul-2026