J/MNRAS/483/4291 Properties of JCMT CO(3-2) molecular clouds (Colombo+, 2019)
The integrated properties of the molecular clouds from the JCMT CO(3-2)
High-Resolution Survey.
Colombo D., Rosolowsky E., Duarte-Cabral A., Ginsburg A., Glenn J.,
Zetterlund E., Hernandez A.K., Dempsey J., Currie M.J.
<Mon. Not. R. Astron. Soc., 483, 4291-4340 (2019)>
=2019MNRAS.483.4291C 2019MNRAS.483.4291C (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Molecular clouds ; Milky Way
Keywords: methods: analytical - techniques: image processing - ISM: clouds -
ISM: structure
Abstract:
We define the molecular cloud properties of the Milky Way first
quadrant using data from the JCMT CO(3-2) High-Resolution Survey. We
apply the Spectral Clustering for Interstellar Molecular Emission
Segmentation (SCIMES) algorithm to extract objects from the
full-resolution data set, creating the first catalogue of molecular
clouds with a large dynamic range in spatial scale. We identify more
than 85000 clouds with two clear sub-samples: ∼35500 well-resolved
objects and ∼540 clouds with well-defined distance estimations. Only
35 per cent of the catalogued clouds (as well as the total flux
encompassed by them) appear enclosed within the Milky Way spiral arms.
The scaling relationships between clouds with known distances are
comparable to the characteristics of the clouds identified in previous
surveys. However, these relations between integrated properties,
especially from the full catalogue, show a large intrinsic scatter
(∼0.5dex), comparable to other cloud catalogues of the Milky Way and
nearby galaxies. The mass distribution of molecular clouds follows a
truncated-power-law relationship over three orders of magnitude in
mass with a form dN/dMαM-1.7 with a clearly defined truncation
at an upper mass of M0∼3x106M☉, consistent with theoretical
models of cloud formation controlled by stellar feedback and shear.
Similarly, the cloud population shows a power-law distribution of size
with dN/dRαR-2.8 with a truncation at R0=70pc.
Description:
The COHRS is a large-scale CO survey that observed the inner Galactic
plane in 12CO (J=3->2) emission using the Heterodyne Array Receiver
Programme B-band instrument on the James Clerk Maxwell Telescope
(JCMT). The current data release mapped a strip of the Milky Way
|b|=<0.5° between 10.25°<l<17.5° and
50.25°<l<55.25°, and |b|=<0.25° between
17.5°<l<50.25°. The survey covers a velocity range of
-30km/s<vLSR<155km/s. The data have a spectral resolution of 1km/s
and an angular resolution of θFWHM=16.6arcsec, achieving a
mean noise level of σRMS∼1K. The J=3-2 transition of the
12CO molecule traces the warm molecular medium (10-50K) around the
active SF regions. For full details about COHRS, refer to Dempsey et
al. (2013ApJS..209....8D 2013ApJS..209....8D).
To decompose clouds in the COHRS data we use the publicly available
Spectral Clustering for Interstellar Molecular Emission Segmentation
(SCIMES) algorithm. In general, SCIMES finds relevant objects within a
dendrogram of emission using spectral clustering. A dendrogram is a
tree representation of image data that encodes the hierarchical
structure emission (e.g. Rosolowsky et al. 2008ApJ...679.1338R 2008ApJ...679.1338R). The
dendrogram is composed of two types of structures: branches, which are
structures which split into multiple substructures, and leaves, which
are structures that have no substructure. Leaves are associated with
the local maxima in the emission. We also consider the trunk, which is
the superstructure that has no parent structure, and contains all
branches and leaves.
The cloud catalogue we produced is presented in Table 1. The whole
catalogue is made of 85020 objects: 73140 (86 per cent) are leaves and
11880 (12 per cent) are branches.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 1317 85020 Contents of the COHRS cloud catalogue
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID Cloud identification number
7- 11 I5 --- DS Structure number within the
dendrogram
13- 32 A20 --- File Sub-cube assignment file name
34- 39 F6.1 pix xcen Centroid position along the sub-cube
x-axis
41- 45 F5.1 pix ycen Centroid position along the sub-cube
y-axis
47- 51 F5.1 pix vcen Centroid position along the sub-cube
velocity
53- 57 F5.2 deg GLON Mean Galactic longitude
59- 63 F5.2 deg GLAT Mean Galactic latitude
65- 69 F5.1 km/s vLSR Mean velocity with respect to the
local standard of rest
71- 78 F8.2 pc Xsun Heliocentric coordinate X
80- 86 F7.2 pc Ysun Heliocentric coordinate Y
88- 94 F7.2 pc Zsun Heliocentric coordinate Z
96-103 F8.2 pc Xgal Galactocentric coordinate X
105-112 F8.2 pc Ygal Galactocentric coordinate Y
114-120 F7.2 pc Zgal Galactocentric coordinate Z
122-127 F6.2 pix apix Uncorrected major semi-axis size
(in pix)
129-134 F6.2 pix bpix Uncorrected minor semi-axis size
(in pix)
136-141 F6.2 pix adcpix Deconvolved major semi-axis size
(in pix)
143-148 F6.2 pix bdcpix Deconvolved minor semi-axis size
(in pix)
150-155 F6.2 pix aexpix ? Extrapolated major semi-axis size
(in pix)
157-162 F6.2 pix bexpix ? Extrapolated minor semi-axis size
(in pix)
164-169 F6.2 pix aexdcpix Extrapolated and deconvolved major
semi-axis size (in pix)
171-176 F6.2 pix bexdcpix Extrapolated and deconvolved minor
semi-axis size (in pix)
178-184 F7.2 arcsec aas Uncorrected major semi-axis size
(in arcsec)
186-191 F6.2 arcsec bas Uncorrected minor semi-axis size
(in arcsec)
193-199 F7.2 arcsec adcas ? Deconvolved major semi-axis size
(in arcsec)
201-206 F6.2 arcsec bdcas ? Deconvolved minor semi-axis size
(in arcsec)
208-214 F7.2 arcsec aexas ? Extrapolated major semi-axis size
(in arcsec)
216-221 F6.2 arcsec bexas ? Extrapolated minor semi-axis size
(in arcsec)
223-229 F7.2 arcsec aexdcas ? Extrapolated and deconvolved major
semi-axis size (in arcsec)
231-236 F6.2 arcsec bexdcas ? Extrapolated and deconvolved minor
semi-axis size (in arcsec)
238-244 F7.2 deg PA [] Position angle with respect to
the cube x-axis
246-255 F10.2 K FCO Integrated flux
257-266 F10.2 K FCOex ? Extrapolated FCO
268-275 F8.1 pix Aexactpix Area defined as projected total
number of pixels (in pix)
277-284 F8.2 pix Aellipsepix Area of the ellipse from a,b
(in pix) (1)
286-294 F9.1 arcsec2 Aexactas Area defined as projected total
number of pixels (in arcsec2)
296-305 F10.2 arcsec2 Aellipseas Area of the ellipse from a,b
(in arcsec2) (1)
307-311 F5.2 K Tpeak Peak brightess temperature within
the cloud
313-316 F4.2 K Tmean Mean brightess temperature within
the cloud
318-323 F6.2 --- SNRpeak Peak signal-to-noise within the
cloud
325-329 F5.2 --- SNRmean Mean signal-to-noise within the
cloud
331-338 F8.2 pc Dist Object distance
340-342 F3.1 --- BType [0/3] Broadcast type, distance
quality (10)
344-349 F6.2 pix Binacc Broadcast inaccuracy
351-355 F5.2 pc Rad Effective radius (2)
357-361 F5.2 km/s sigv Velocity dispersion
363-371 F9.2 K.km.pc2/s LCO CO luminosity (3)
373-382 F10.2 Msun Mlum Mass from the CO luminosity
384-393 F10.2 Msun Mvir Mass from the virial theorem (4)
395-400 F6.2 km2/s2/pc scalpar Scaling parameter (5)
402-407 F6.2 K.km/s lCO Integrated CO luminosity
409-430 E22.20 cm-2 NH2 H2 column density
432-438 F7.2 Msun/pc2 surfdens Surface density
440-448 F9.2 pc2.km/s Volume Volume (6)
450-456 F7.2 --- alpha Virial parameter (7)
458-462 F5.2 pc Raddc Deconvolved effective radius
464-468 F5.2 km/s sigvdc Deconvolved velocity dispersion
470-479 F10.2 Msun Mvirdc Deconvolved virial mass
481-486 F6.2 km2/s2/pc scalpardc Deconvolved scaling parameter
488-493 F6.2 K.km/s lCOdc Deconcolved integrated CO
luminosity
495-516 E22.20 cm-2 NH2dc Deconvolved NH2 column density
518-524 F7.2 Msun/pc2 surfdensdc Deconvolved surface density
526-534 F9.2 pc2.km/s volumedc Deconvolved volume
536-542 F7.2 --- alphadc Deconvolved virial parameter
544-548 F5.2 pc Radex ? Extrapolated effective radius
550-554 F5.2 km/s sigvex ? Extrapolated velocity dispersion
556-564 F9.2 K.km.pc2/s LCOex ? Extrapolated CO luminosity
566-575 F10.2 Msun Mlumex ? Extrapolated mass from the CO
luminosity
577-586 F10.2 Msun Mvirex ? Extrapolated virial mass
588-593 F6.2 km2/s2/pc scalparex ? Extrapolated scaling parameter
595-600 F6.2 K.km/s lCOex ? Extrapolated integrated CO
luminosity
602-623 E22.20 cm-2 NH2ex ? Extrapolated NH2 column density
625-631 F7.2 Msun/pc2 surfdensex ? Extrapolated surface density
633-641 F9.2 pc2.km/s volumeex ? Extrapolated volume
643-649 F7.2 --- alphaex ? Extrapolated virial parameter
651-655 F5.2 pc Radexdc Extrapolated and deconvolved
effective radius
657-661 F5.2 km/s sigvexdc ? Extrapolated and deconvolved
velocity dispersion
663-672 F10.2 Msun Mvirexdc ? Extrapolated and deconvolved
virial mass
674-680 F7.2 km2/s2/pc scalparexdc ? Extrapolated and deconvolved
scaling parameter
682-688 F7.2 K.km/s lCOexdc ? Extrapolated and deconvolved
integrated CO luminosity
690-711 E22.20 cm-2 NH2exdc ? Extrapolated and deconvolved NH2
column density
713-720 F8.2 Msun/pc2 surfdensexdc ? Extrapolated and deconvolved
surface density
722-730 F9.2 pc2.km/s volumeexdc ? Extrapolated and deconvolved
volume
732-738 F7.2 --- alphaexdc ? Extrapolated and deconvolved
virial parameter
740-745 I6 --- Npix Number of pixel within the cloud
747-749 I3 --- Nleaves Number of leaves within the cloud
751-753 F3.1 --- edge The cloud is on the cube lower or
upper border
755-759 I5 --- parent Cloud parental structure ID
761-765 I5 --- ancestor Cloud parental structure ID at the
bottom of the hierarchy
767 A1 --- StrucType Structure type (8)
769-775 F7.2 pc DistArm Distance to the associated spiral
arm
777-778 A2 --- Arm Spiral arm associated with the
cloud (9)
780-786 F7.2 pc e_Xsun Error on Xsun
788-794 F7.2 pc e_Ysun Error on Ysun
796-801 F6.2 pc e_Zsun [] Error on Zsun
803-809 F7.2 pc e_Xgal Error on Xgal
811-817 F7.2 pc e_Ygal Error on Ygal
819-824 F6.2 pc e_Zgal [] Error on Zgal
826-829 F4.2 pix e_apix ? Error on apix
831-834 F4.2 pix e_bpix ? Error on bpix
836-839 F4.2 pix e_adcpix ? Error on adcpix
841-844 F4.2 pix e_bdcpix ? Error on bdcpix
846-849 F4.2 pix e_aexpix ? Error on aexpix
851-854 F4.2 pix e_bexpix ? Error on bexpix
856-860 F5.2 pix e_aexdcpix ? Error on aexdcpix
862-865 F4.2 pix e_bexdcpix ? Error on bexdcpix
867-870 F4.2 arcsec e_aas ? Error on aas
872-875 F4.2 arcsec e_bas ? Error on bas
877-880 F4.2 arcsec e_adcas ? Error on adcas
882-885 F4.2 arcsec e_bdcas ? Error on bdcas
887-891 F5.2 arcsec e_aexas ? Error on aexas
893-897 F5.2 arcsec e_bexas ? Error on bexas
899-904 F6.2 arcsec e_aexdcas ? Error on aexdcas
906-910 F5.2 arcsec e_bexdcas ? Error on bexdcas
912-918 F7.2 pc e_Dist Error on Dist
920-924 F5.2 pc e_Rad ? Error on Rad
926-929 F4.2 km/s e_sigv ? Error on sigv
931-939 F9.2 K.km.pc2/s e_LCO Error on LCO
941-950 F10.2 Msun e_Mlum Error on Mlum
952-961 F10.2 Msun e_Mvir ? Error on Mvir
963-969 F7.2 km2/s2/pc e_scalpar ? Error on scalpar
971-979 F9.2 K.km/s e_lCO ? Error on lCO
981-1002 E22.20 cm-2 e_NH2 ? Error on NH2
1004-1010 F7.2 Msun/pc2 e_surfdens ? Error on surfdens
1012-1019 F8.2 pc2.km/s e_Volume ? Error on volume
1021-1026 F6.2 --- e_alpha ? Error on alpha
1028-1032 F5.2 pc e_Raddc ? Error on Raddc
1034-1037 F4.2 km/s e_sigvdc ? Error on sigvdc
1039-1048 F10.2 Msun e_Mvirdc ? Error on Mvirdc
1050-1056 F7.2 km2/s2/pc e_scalpardc ? Error on scalpardc
1058-1066 F9.2 K.km/s e_lCOdc ? Error on lCOdc
1068-1089 E22.20 cm-2 e_NH2dc ? Error on NH2dc
1091-1097 F7.2 Msun/pc2 e_surfdensdc ? Error on surfdensdc
1099-1106 F8.2 pc2.km/s e_volumedc ? Error on volumedc
1108-1113 F6.2 --- e_alphadc ? Error on alphadc
1115-1119 F5.2 pc e_Radex ? Error on Radex
1121-1124 F4.2 km/s e_sigvex ? Error on sigvex
1126-1134 F9.2 K.km.pc2/s e_LCOex ? Error on LCOex
1136-1145 F10.2 Msun e_Mlumex ? Error on Mlumex
1147-1156 F10.2 Msun e_Mvirex ? Error on Mvirex
1158-1164 F7.2 km2/s2/pc e_scalparex ? Error on sclaparex
1166-1174 F9.2 K.km/s e_lCOex ? Error on lCOex
1176-1197 E22.20 cm-2 e_NH2ex ? Error on NH2ex
1199-1206 F8.2 Msun/pc2 e_surfdensex ? Error on surfdensex
1208-1216 F9.2 pc2.km/s e_volumeex ? Error on volumeex
1218-1224 F7.2 --- e_alphaex ? Error on alphaex
1226-1230 F5.2 pc e_Radexdc ? Error on Radexdc
1232-1235 F4.2 km/s e_sigvexdc ? Error on sigvexdc
1237-1246 F10.2 Msun e_Mvirexdc ? Error on Mvirexdc
1248-1254 F7.2 km2/s2/pc e_scalparexdc ? Error on scalparexdc
1256-1265 F10.2 K.km/s e_lCOexdc ? Error on lCOexdc
1267-1288 E22.20 cm-2 e_NH2exdc ? Error on NH2exdc
1290-1298 F9.2 Msun/pc2 e_surfdensexdc ? Error on surfdensexdc
1300-1308 F9.2 pc2.km/s e_volumeexdc ? Error on volumeexdc
1310-1317 F8.3 --- e_alphaexdc ? Error on alphaexdc
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Note (1): Aellipse=8πln2xaxb where a is the semimajor axis and b is the
semiminor axis
Note (2): The effective radius of the cloud is generated from quadrature sum of
the semimajor and semiminor axes:
Radd=ηsqrt(a2+b2), where η=1.91 is assumed from
Rosolowsky & Leroy (2006PASP..118..590R 2006PASP..118..590R) to relate the quadrature sum
of the two semi-axes and the radius of a spherical cloud.
Note (3): The luminosity is calculated as LCO=FCOxDist2, where FCO is the
integrated emission within the isosurface (the flux) and Dist is the
distance to the structure
Note (4): We make a dynamical measurement of the cloud mass assuming the clouds
are virialized, spherical objects.
We called this measurement virial mass: Mvir=1040sigv2Rad,
where we ignore the contribution from external pressure and magnetic
fields (Rosolowsky & Leroy 2006PASP..118..590R 2006PASP..118..590R)
Note (5): The scaling parameter is defined as scalparam=sigv2/Rad
Note (6): The volume is defined as: volume=sigvπRad2
Note (7): The ratio between virial and luminous mass gives the virial parameter
alpha=1.12Mvir/Mlum, which is often used to characterize the
deviation of a cloud from virial equilibrium
Note (8): Structure type as follows:
L = (leaf) a structure without children
B = (branch) a structure with children and parent
T = (trunk) structure with children and without parent
Note (9): Spiral arm as follows:
Sa = Sagittarius
Sc = Scutum
Lo = Local
Pe = Perseus
No = Norma
Note (10): BType as follows:
0 = exact
1 = broadcasted
2 = closest
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(End) Ana Fiallos [CDS] 28-Jul-2022