J/ApJ/780/173 Masses of giant molecular clouds in Milky Way (Battisti+, 2014)
The dense gas mass fraction of molecular clouds in the Milky Way.
Battisti A.J., Heyer M.H.
<Astrophys. J., 780, 173 (2014)>
=2014ApJ...780..173B 2014ApJ...780..173B
ADC_Keywords: Milky Way ; Galactic plane ; Interstellar medium ;
Molecular clouds ; Velocity dispersion
Keywords: ISM: clouds - ISM: kinematics and dynamics - stars: formation
Abstract:
The mass fraction of dense gas within giant molecular clouds (GMCs) of
the Milky Way is investigated using 13CO data from the Five College
Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam
Galactic Plane Survey (BGPS) of 1.1mm dust continuum emission. A
sample of 860 compact dust sources are selected from the BGPS catalog
and kinematically linked to 344 clouds of extended (>3') 13CO J=1-0
emission. Gas masses are tabulated for the full dust source and
subregions within the dust sources with mass surface densities greater
than 200M☉/pc2, which are assumed to be regions of enhanced
volume density. Masses of the parent GMCs are calculated assuming
optically thin 13CO J=1-0 emission and local thermodynamic
equilibrium conditions. The mean fractional mass of dust sources to
host GMC mass is 0.11+0.12-0.06_. The high column density
subregions comprise 0.07+0.13-0.05 of the mass of the cloud. Owing
to our assumptions, these values are upper limits to the true mass
fractions. The fractional mass of dense gas is independent of GMC mass
and gas surface density. The low dense gas mass fraction suggests that
the formation of dense structures within GMCs is the primary
bottleneck for star formation. The distribution of velocity
differences between the dense gas and the low density material along
the line of sight is also examined. We find a strong, centrally peaked
distribution centered on zero velocity displacement. This distribution
of velocity differences is modeled with radially converging flows
toward the dense gas position that are randomly oriented with respect
to the observed line of sight. These models constrain the infall
velocities to be 2-4km/s for various flow configurations.
Description:
The Boston University-Five College Radio Astronomy Observatory
(BU-FCRAO) Galactic Ring Survey (GRS; Jackson et al.,
2006ApJS..163..145J 2006ApJS..163..145J) and the Exeter-FCRAO Survey of the Galactic Plane
(unpublished) imaged the 13CO J=1-0 emission along the Galactic
Plane with the 14m telescope of the FCRAO. The GRS covers the Galactic
longitude range l=18°-55.7° and latitude range of
|b|≤1° with a median sensitivity of 0.28K in main beam
temperature units within 0.2km/s wide channels. The Exeter-FCRAO
Survey of 12CO and 13CO J=1-0 emission spans longitudes 55° to
100° and 140° to 195° with varying latitude coverage but
no less than ±1°. The median sensitivity of the 13CO data
within 0.13km/s wide channels is 0.5K in main beam temperature units.
Both surveys are fully sampled, so the angular resolution of the
13CO data used in this study is 47'' corresponding to the full width
at half-maximum (FWHM) of the 14m telescope at 110.201GHz.
The Bolocam Galactic Plane Survey (BGPS) imaged the 1.1mm dust
continuum emission between Galactic longitudes of -10°<l<90°
and latitudes |b|≤0.5° with the Caltech Submillimeter
Observatory. The 1σ surface brightness sensitivity ranges from
11-53mJy/beam and the FWHM angular resolution is 33''.
We have examined the properties of the host Giant Molecular Clouds
(GMCs) associated with a limited sample of 1.1mm dust continuum BGPS
sources from the catalog of Rosolowsky et al. 2010, J/ApJS/188/123).
The GMCs linked to each selected BGPS source are identified by regions
of 13CO(J=1-0) emission.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 91 437 Giant Molecular Cloud (GMC) properties and dust masses
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See also:
J/ApJ/799/29 : BGPS. XII. DR2 distance catalog (Ellsworth-Bowers+, 2015)
J/ApJS/209/2 : The BGPS. X. Dense molecular gas (Shirley+, 2013)
J/ApJ/770/39 : BGPS VIII. MIR kinematic distances (Ellsworth-Bowers+, 2013)
J/MNRAS/431/1587 : GRS/BGPS sources in Galactic Plane (Eden+, 2013)
J/MNRAS/422/3178 : Distances of 793 BGPS sources (Eden+, 2012)
J/ApJ/741/110 : The BGPS. VII. Massive star-forming regions (Dunham+, 2011)
J/ApJ/731/90 : Mid-IR content of BGPS sources (Dunham+, 2011)
J/ApJS/195/14 : The Bolocam Galactic Plane Survey. V. (Schlingman+, 2011)
J/ApJS/188/123 : The Bolocam Galactic Plane Survey. II. (Rosolowsky+, 2010)
J/ApJ/723/492 : Physical properties of GRS clouds (Roman-Duval+, 2010)
J/ApJ/721/137 : The Bolocam Galactic Plane Survey (BGPS) (Bally+, 2010)
J/ApJ/699/1153 : Kinematic distances to GRS clouds (Roman-Duval+, 2009)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJS/182/131 : Molecular clouds and clumps in the GRS (Rathborne+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Source [2430/6504] Sequence number of the primary
source in the Bolocam Galactic Plane Survey
(BGPS) catalog (1)
6- 8 F3.1 K Tthr [0.5/6.8] Threshold temperature to define the
giant molecular cloud
10- 15 F6.3 deg GLON Galactic longitude
17- 22 F6.3 deg GLAT Galactic latitude
24- 28 F5.1 km/s Vlsr [4/124] Local standard of rest velocity of
the giant molecular cloud
30- 34 F5.2 kpc Dkin [0.9/15] Kinematic distance to the giant
molecular cloud
36- 40 F5.2 pc Rad [1/34] Radius of the giant molecular cloud
42- 46 F5.2 pc e_Rad [0.01/15.1] Uncertainty in Rad
48- 51 F4.2 km/s sigma [0.6/5] Velocity dispersion of the giant
molecular cloud
53- 56 F4.2 km/s e_sigma [0/2.48] Uncertainty in sigma
58- 62 F5.1 kMsun Mass [0.7/726] Mass of the giant molecular cloud (2)
64- 68 F5.1 kMsun e_Mass [0/463] Uncertainty in Mass (3)
70- 73 F4.1 kMsun Md1 [0.2/100] Total dust mass derived from all
primary and secondary sources in the Galactic
Plane Survey (BGPS) within the cloud (4)
75- 78 F4.1 kMsun e_Md1 [0.1/32] Uncertainty in Md1
80- 83 F4.1 kMsun Md2 [0/71] Total dust mass of BGPS source pixels (5)
85- 88 F4.1 kMsun e_Md2 [0/29] Uncertainty in Md2
90- 91 I2 --- Ns [1/22] Total number of BGPS sources within the
giant molecular cloud (6)
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Note (1): We have examined the properties of the host Giant Molecular Clouds
(GMCs) associated with a limited sample of 1.1mm dust continuum BGPS
sources from the catalog of Rosolowsky et al. 2010, J/ApJS/188/123).
The GMCs linked to each selected BGPS source are identified by regions of
13CO J=1-0 emission. The BGPS source that links the 13CO cloud as a
region of interest, is labeled the primary source for the cloud.
Note (2): Mass=0.41[6.2Rgal+18.7]L13M☉ (Equation (2)), where L13 is
the 13CO luminosity, and the term in square brackets accounts for the
varying 12C to 13C abundance ratio with Galactocentric radius, Rgal
(Milam et al., 2005ApJ...634.1126M 2005ApJ...634.1126M).
Note (3): The standard deviation of mass value determined from the sequence of
antenna temperature threshold for which the cloud is well distinguished
from extented signal. If the number of thresholds is less than 3, then the
assigned error is the statistical error calculated by CPROPS through the
bootstrap method (Rosolowsky & Leroy, 2006PASP..118..590R 2006PASP..118..590R).
Note (4): The mass of each BGPS source can be estimated from its integrated flux
density, S1.1mm, assuming that the dust emission at 1.1mm is optically
thin and well characterized by a single temperature and opacity:
Mdust = (Dkin2S1.1mm)/B1.1mm(Tdust)κ1.1mm (Eq.5),
where
* Dkin is the distance to the cloud harboring the BGPS source,
* B1.1mm is the Planck function evaluated at λ=1.1mm and dust
temperature Tdust, and
* κ1.1mm=0.0114cm2/g is the dust opacity per gram of gas
(Ossenkopf & Henning 1994, J/A+A/291/943) and includes a
gas-to-dust ratio of 100.
The dust continuum source requirements selects 437 primary sources
from the BGPS catalog. An additional 578 secondary BGPS sources
whose (l,b) coordinates reside within the projected mask of these
isolated GMCs are included in the accounting of the total dust mass.
Note (5): With the mass surface density
Σdust=Mdust/πR2dust>200M☉/pc2, where Rdust is
the effective radius of the dust continuum source.
Note (6): Of the 437 giant molecular clouds identified, 212 contain a singular
dust source, 100 contain two dust sources, 52 contain three sources, and 73
contain four or more sources.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 30-Jan-2015