J/ApJS/275/35 CO molecular clouds from the MWISP project (Sun+, 2024)
Molecular clouds in the outer Milky Way disk: sample, integrated properties, and
radial trends with Galactocentric radius.
Sun Y., Yang Ji, Yan Q.-Z., Zhang S., Su Y., Chen X., Zhou X., Ma Y.,
Yuan L.
<Astrophys. J. Suppl. Ser., 275, 35 (2024)>
=2024ApJS..275...35S 2024ApJS..275...35S
ADC_Keywords: Molecular clouds; Milky Way; Carbon monoxide; Velocity dispersion;
Interstellar medium
Keywords: Molecular clouds ; Milky Way Galaxy ; Milky Way disk ;
CO line emission ; Interstellar line emission
Abstract:
We present a catalog of 32162 12CO molecular clouds that covers the
northern outer Galactic plane (l=[15°,165°] and
l=[195°,230°], and b=[-5.25°,+5.25°]). The catalog was
produced using a DBSCAN algorithm applied to the Milky Way Imaging
Scroll Painting project data. We systematically analyze both the
integrated properties and scaling relationships of these molecular
clouds across different Galactocentric radii (8<RGC<26kpc). An
interesting finding is that each cloud property's mean, median, and
maximum values generally decrease systematically with increasing
RGC, approximated quantitatively by exponential functions. The mass
and size spectra for the entire sample show power-law indices of
γ=-2.00±0.13 and an upper mass limit of
M0=(4.5±2.8)x106M☉, and γ=-3.68±0.48 with an
upper size limit of R0=144±80pc, respectively. These spectra
exhibit steeper slopes and reduced upper limits as RGC increases.
The derived scaling relations are M=12.00Reff2.41±0.003^,
σv=0.25Reff0.66±0.003, and αvir=37.2M-0.40±0.002
for the whole outer Galaxy clouds. These scaling relations show
slightly steeper correlations observed in more distant locations and
notably deviate from Larson's relations. We find that 44.3% of the
molecular mass resides in gravitationally bound structures, a
proportion significantly higher than systematic studies from the CfA
survey and external galaxies. Moreover, comparisons among different
RGC subsamples also reveal a decrease in the amount of bound mass with
increasing RGC. The scale length of the molecular disk is estimated to
be approximately 2kpc. These results, based on a constant CO
conversion factor of XCO=2.0x1020cm-2(K.km.s-1)-1, may be
slightly altered by variations in XCO. In summary, our findings
provide robust evidence for the influence of Galactic evolution on
molecular cloud properties, at least in the outer Galaxy region
studied.
Description:
Detailed descriptions of the instrument and observation strategy used
for the Milky Way Imaging Scroll Painting (MWISP) survey can be found
in the literature. In this study, we utilize MWISP data products that
were processed with several steps, including the subtraction of the
first-order baseline, the correction of the main-beam efficiency, and
the removal of conspicuous bad channels. Please refer to
Su+ (2019ApJS..240....9S 2019ApJS..240....9S) for detailed information on these processes,
and the more refined data-cleansing process is still ongoing.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 135 32162 Molecular clouds in the Outer Galaxy identified
from the MWISP survey
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See also:
J/A+A/275/67 : Velocity Field of the outer Galaxy (Brand+ 1993)
J/A+A/327/325 : Distances of molecular cloud (May+, 1997)
J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)
J/ApJS/144/47 : Outer galaxy molecular cloud catalog (Brunt+, 2003)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJS/182/131 : Molecular clouds and clumps in the GRS (Rathborne+, 2009)
J/ApJ/723/492 : Physical data of GRS molecular clouds (Roman-Duval+, 2010)
J/ApJ/734/65 : CI radial velocities with HST/STIS (Jenkins+, 2011)
J/A+A/542/A108 : Giant molecular clouds in M33 (Gratier+, 2012)
J/ApJ/784/3 : The PAWS cat. of GMCs and islands in M51 (Colombo+, 2014)
J/A+A/566/A37 : Iron abundances for 42 Galactic Cepheids (Genovali+, 2014)
J/AJ/147/46 : Properties of clumps in the NAN complex (Zhang+, 2014)
J/ApJ/798/L27 : CO obs. of molecular clouds in the 2nd quadrant (Sun+, 2015)
J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)
J/ApJ/833/229 : Star forming cloud-giant molecular clouds (Lee+, 2016)
J/A+A/585/A150 : On the metallicity of open clusters. III. (Netopil+, 2016)
J/ApJ/834/57 : MW molecular clouds from 12CO (Miville-Deschenes+, 2017)
J/MNRAS/470/2539 : Radiation fields of the Milky Way (Popescu+, 2017)
J/A+A/601/A124 : Clouds in SEDIGISM field (Schuller+, 2017)
J/ApJS/230/17 : CO obs. of MCs in the Extreme Outer Gal. region (Sun+, 2017)
J/A+A/598/A30 : Massive star forming molecular clumps Tkin (Tang+, 2017)
J/ApJ/857/19 : ALMA view of GMCs in NGC 300 (Faesi+, 2018)
J/ApJ/860/172 : Cloud-scale molecular gas in 15 galaxies (Sun+, 2018)
J/A+A/611/A6 : ATLASGAL massive clumps H2CO data (Tang+, 2018)
J/MNRAS/473/1059 : Complete sample of Gal. clump properties (Urquhart+, 2018)
J/ApJS/241/1 : Surveys of clumps & cores in Cygnus X. I. (Cao+, 2019)
J/MNRAS/483/4291 : Properties of JCMT CO(3-2) molecular clouds (Colombo+, 2019)
J/ApJ/885/131 : High-mass SFR plx & proper motion with VLBI (Reid+, 2019)
J/A+A/632/A58 : Physical properties of CHIMPS clumps (Rigby+, 2019)
J/ApJ/887/114 : VLA ∼8-10GHz obs. of WISE Gal. HII regions (Wenger+, 2019)
J/A+A/633/A147 : FQS. Galactic Plane CO survey (Benedettini+, 2020)
J/ApJ/901/L8 : Molecular gas properties of 70 PHANGS-ALMA gal. (Sun+, 2020)
J/A+A/654/A144 : 13CO (1-0) data molecular cloud cat. (Benedettini+, 2021)
J/MNRAS/500/3027 : The SEDIGISM survey: molecular clouds (Duarte-Cabral+, 2021)
J/ApJS/257/43 : PHANGS-ALMA: CO(2-1) imaging of gal. (Leroy+, 2021)
J/ApJS/252/20 : CO survey of the CMa OB1 complex (Lin+, 2021)
J/MNRAS/505/4048 : WISDOM Project IX study of GMCs in NGC 4429 (Liu+, 2021)
J/ApJS/254/3 : CO obs. of molecular clouds in the MW midplane (Ma+, 2021)
J/MNRAS/500/3064 : The SEDIGISM survey: First Data Release (Schuller+, 2021)
J/ApJS/252/1 : OH and HI data in molecular clouds (Tang+, 2021)
J/A+A/658/A54 : Molecular cloud assoc. to MW spiral arms (Colombo+, 2022)
J/MNRAS/510/3389 : High-mass star formation evol. trends (Urquhart+, 2022)
J/ApJS/268/1 : Mol. clouds CO obs. in the 3rd Gal. quadrant (Dong+, 2023)
J/AJ/165/106 : Mol. clouds in section of 3rd Gal. quadrant (Wang+, 2023)
J/AJ/167/228 : Physical properties of 221 clumps (Luo+, 2024)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Seq [1/32162] Internal index number
7- 13 F7.3 deg GLON [15/230] Cloud centroid galactic
longitude
15- 20 F6.3 deg GLAT [-5.2/5.2] Cloud centroid galactic
latitude
22- 27 F6.1 km/s Velc [-123.2/86.3] Cloud centroid Local
Standard of Rest velocity
29- 32 F4.2 km/s sigmaV [0.1/5.4] Velocity dispersion
34- 40 F7.3 deg GLONpk [15/230] Peak CO emission galactic
longitude
42- 47 F6.3 deg GLATpk [-5.2/5.3] Peak CO emission galactic
latitude
49- 54 F6.1 km/s Velpk [-123/87] Peak CO emission Local
Standard of Rest velocity
56- 59 F4.1 K Tpk [1/48.8] Peak CO emission main-beam
temperature
61- 67 F7.1 arcmin2 Area [1/38544] Angular area of cloud
69- 76 F8.1 K.km/s.arcmin2 Flux [0.4/388803] Total cloud flux
78- 81 F4.1 kpc Dist [0.8/22.5] Heliocentric distance
83- 86 F4.1 kpc RGC [8.1/26.7] Galactocentric distance
88- 92 F5.1 pc Reff [0.2/101.4] Cloud effective radius
94- 97 F4.1 K Tex [3.9/52.3] Cloud excitation
temperature
99- 107 F9.1 Msun Mass [0.3/2545399] Cloud mass
109- 112 F4.1 Msun/pc2 SigmaMC [1.3/82] Cloud mass surface density
114- 118 F5.1 --- alphaVir [0.4/141] Cloud virial parameter
120- 124 F5.1 cm-3 nH2 [3/381] Cloud mean H2 number
density
126- 133 F8.1 K/cm3 Pint/kB [30/377087.4] Cloud internal pressure
135 A1 --- Res Cloud resolved? (1)
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Note (1): Meaning the cloud satisfies the Area≥2.5x2.5arcmin2 criterion.
Y = cloud is resolved.
N = cloud is unresolved.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 23-Oct-2025