J/ApJ/723/492 Physical properties of GRS molecular clouds (Roman-Duval+, 2010)
Physical properties and Galactic distribution of molecular clouds identified in
the Galactic Ring Survey.
Roman-Duval J., Jackson J.M., Heyer M., Rathborne J., Simon R.
<Astrophys. J., 723, 492-507 (2010)>
=2010ApJ...723..492R 2010ApJ...723..492R
ADC_Keywords: Molecular clouds ; Milky Way ; Radio lines ; Surveys
Keywords: Galaxy: structure - ISM: clouds - molecular data
Abstract:
We derive the physical properties of 580 molecular clouds based on
their 12CO and 13CO line emission detected in the University of
Massachusetts-Stony Brook (UMSB) and Galactic Ring surveys (GRS).
We provide a range of values of the physical properties of molecular
clouds, and find a power-law correlation between their radii and
masses, suggesting that the fractal dimension of the interstellar
medium is around 2.36. This relation, M=(228±18)R2.36±0.04,
allows us to derive masses for an additional 170 Galactic Ring Survey
(GRS) molecular clouds not covered by the UMSB survey. We derive the
Galactic surface mass density of molecular gas and examine its spatial
variations throughout the Galaxy. We find that the azimuthally
averaged Galactic surface density of molecular gas peaks between
Galactocentric radii of 4 and 5kpc. Although the Perseus arm is not
detected in molecular gas, the Galactic surface density of molecular
gas is enhanced along the positions of the Scutum-Crux and Sagittarius
arms.
Description:
In this paper, we derive the physical properties (mass, radius,
surface density, etc.) and the Galactic mass distribution of a sample
of 750 molecular clouds identified in the GRS (Rathborne et al. 2009,
Cat. J/ApJS/182/131), for which kinematic distances are available from
Roman-Duval et al. (2009, Cat. J/ApJ/699/1153). The sample of
molecular clouds used in this analysis was identified by their 13CO
J=1->0 emission in the BU-FCRAO GRS (Jackson et al.
2006ApJS..163..145J 2006ApJS..163..145J). The GRS was conducted using the FCRAO 14m
telescope in New Salem, Massachusetts between 1998 and 2005. We also
make use of the 12CO University of Massachusetts-Stony Brook (UMSB)
survey (Sanders et al. 1986ApJS...60....1S 1986ApJS...60....1S; Clemens et al.
1986ApJS...60..297C 1986ApJS...60..297C), a joint program between FCRAO and the State
University of New York at Stony Brook performed between 1981 November
and 1984 March. All of the observations were obtained using the FCRAO
14m telescope.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 94 749 Catalog of Molecular Cloud's Masses and Physical
Properties
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See also:
J/ApJS/196/18 : CO survey of galactic molecular clouds. II. (Bieging+, 2011)
J/MNRAS/410/1237 : Red MSX survey (RMS) massive young stars (Urquhart+, 2011)
J/PASJ/62/557 : CO clouds in the GC from NANTEN (Takeuchi+, 2010)
J/ApJ/699/1153 : Kinematic distances to GRS molecular clouds (Roman-Duval+,
2009)
J/ApJS/182/131 : Molecular clouds and clumps in the GRS (Rathborne+, 2009)
J/ApJ/672/930 : CO clouds in third Galactic quadrant (Vazquez+, 2008)
J/PASJ/57/917 : CO molecular clouds in southern Galactic Warp (Nakagawa+,
2005)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- --- [GRSMC]
7- 19 A13 --- GRSMC GRS [Galactic Ring Survey] molecular cloud
name (G0LL.ll+0B.bb)
21- 25 F5.2 deg GLON Galactic longitude
27- 31 F5.2 deg GLAT Galactic latitude
33- 38 F6.2 km/s VLSR Local Standard of Rest velocity
40- 43 F4.2 km/s DelV Full-Width at Half-Maximum velocity dispersion
45- 48 F4.1 pc Rad Physical radius
50- 55 E6.2 Msun Mass Molecular cloud mass
57- 62 E6.2 Msun e_Mass Uncertainty in Mass
64- 69 F6.1 cm-3 nH2 Mean number density of H2
71- 74 F4.2 K Tex Mean excitation temperature
76- 79 F4.2 --- tau Mean 13CO center-of-line optical depth τ
81- 85 F5.1 Msun/pc2 Sigma Mean surface mass density of the cloud Σ
87- 92 F6.2 --- alpha Virial α parameter (1)
94 A1 --- Note [io] Cloud inside (i) or outside (o) the
University of Massachusetts-Stony Brook (UMSB)
Survey.
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Note (1): α is defined as the ratio of the virial mass to the mass
α=Mvir/M.
This means that clouds having α>1 are not gravitionally bound.
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Nomenclature note:
Molecular clouds are in the dictionary of nomenclature.
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 16-Jul-2012