J/MNRAS/493/351 A large catalogue of molecular clouds (Chen+, 2020)
A large catalogue of molecular clouds with accurate distances within 4 kpc of
the Galactic disc.
Chen B.-Q., Li G.-X., Yuan H.-B., Huang Y., Tian Z.-J., Wang H.-F.,
Zhang H.-W., Wang C., Liu X.-W.
<Mon. Not. R. Astron. Soc., 493, 351-361 (2020)>
=2020MNRAS.493..351C 2020MNRAS.493..351C (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Interstellar medium ; Milky Way ; Extinction ;
Optical ; Infrared
Keywords: ISM: clouds - dust, extinction - Galaxy: structure
Abstract:
We present a large, homogeneous catalogue of molecular clouds within
4kpc from the Sun at low Galactic latitudes (|b|<10°) with
unprecedented accurate distance determinations. Based on the 3D dust
reddening map and estimates of colour excesses and distances of over
32 million stars presented in Chen et al. (2019MNRAS.483.4277C 2019MNRAS.483.4277C), we
have identified 567 dust/molecular clouds with a hierarchical
structure identification method and obtained their distance estimates
by a dust model fitting algorithm. The typical distance uncertainty is
less than 5 per cent. As far as we know, this is the first large
catalogue of molecular clouds in the Galactic plane with distances
derived in a direct manner. The clouds are seen to lie along the
Sagittarius, Local and Perseus Arms. In addition to the known
structures, we propose the existence of a possible spur, with a pitch
angle of about 34°, connecting the Local and the Sagittarius Arms
in the fourth quadrant. We have also derived the physical properties
of those molecular clouds. The distribution of cloud properties in
different parameter spaces agrees grossly with the previous results.
Our cloud sample is an ideal starting point to study the concentration
of dust and gas in the solar vicinity and their star formation
activities.
Description:
In Chen et al. (2019MNRAS.483.4277C 2019MNRAS.483.4277C) (Paper I), we have calculated the
values of colour excesses E(G-KS), E(GBP-GRP), and E(H-KS) of
more than 56 million stars located at low Galactic latitudes
(|b|<10°). In doing so, we combined the high-quality optical
photometry from Gaia DR2 (Gaia Collaboration, 2018A&A...616A...1G 2018A&A...616A...1G,
Cat. I/345) with the near-IR photometry from the Two Micron All Sky
Survey (2MASS; Skrutskie et al. 2006AJ....131.1163S 2006AJ....131.1163S, Cat. VII/233) and
the Wide-Field Infrared Survey Explorer (Wright et al.
2010AJ....140.1868W 2010AJ....140.1868W). The machine learning algorithm random forest
Regression was applied to the photometric data to obtain values of
colour excesses of the individual stars, using a training data sample
constructed from spectroscopic surveys. Distances estimated by
Bailer-Jones et al. (2018AJ....156...58B 2018AJ....156...58B, Cat. I/347), who transfer
the Gaia DR2 parallaxes to distances using a simple Bayesian approach,
were adopted for the stars. A simple cut of the Gaia DR2 parallax
uncertainties of smaller than 20 per cent was applied to exclude the
stars with large distance errors.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 79 567 Catalogue of molecular clouds
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/567] Internal object identifier
5- 12 F8.3 deg GLON [] Galactic longitude
14- 19 F6.3 deg GLAT Galactic latitude
21- 26 F6.3 deg2 Omega Solid angle (1)
28- 33 F6.3 pc r Linear radius of the molecular cloud (2)
35- 40 F6.1 pc d0 Distance to the cloud
42- 46 F5.1 pc e_d0 Error on d0
48- 53 F6.1 pc deltad Width (depth) of the molecular cloud
55- 59 F5.1 pc e_deltad Error on deltad
61- 64 F4.2 mag E(BP-RP) Average colour excess E(BP-RP) of the cloud
66- 73 F8.1 Msun M Mass of the cloud (3)
75- 79 F5.1 Msun/pc2 Sigma Surface mass density of the cloud (4)
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Note (1): The solid angle subtended by an identified molecular cloud is
computed by integrating that of all pixels belonging to the cloud:
Ω=ΣNi=0ΔlΔbcosbi, where i is the index
of a pixel belonging the cloud, Δl=Δb=0.1° the angular
width of the pixel and bi the Galactic latitude of the ith pixel
Note (2): The linear radius of the cloud is computed as r=sqrt(S/π), where
S=Ωd02 is the area of the cloud
Note (3): We estimate the mass of each cloud, assuming that the dust is
distributed as a thin sheet at its centre position, see equation 6
Note (4): The surface mass density of the molecular cloud is calculated as
Σ=M/S
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History:
From electronic version of the journal
References:
Chen et al., Paper I 2019MNRAS.483.4277C 2019MNRAS.483.4277C
(End) Ana Fiallos [CDS] 30-Mar-2023