J/ApJ/910/131 Molecular gas distribution from MWISP CO survey (Su+, 2021)
Molecular gas distribution perpendicular to the Galactic Plane.
Su Y., Yang J., Yan Q.-Z., Zhang S., Wang H., Sun Y., Chen Z., Wang C.,
Zhou X., Chen X., Jiang Z., Wang M.
<Astrophys. J., 910, 131 (2021)>
=2021ApJ...910..131S 2021ApJ...910..131S
ADC_Keywords: Molecular clouds; Carbon monoxide; Galactic plane;
Velocity dispersion
Keywords: Interstellar medium ; Molecular clouds ; Surveys ; Milky Way disk ;
Interstellar dynamics ; Stellar-interstellar interactions
Abstract:
We use the ∼370deg2 data from the MWISP CO survey to study the
vertical distribution of the molecular clouds (MCs) toward the tangent
points in the region of l=[+16°,+52°] and |b|<5.1. We find
that the molecular disk consists of two components with a layer
thickness (FWHM) of ∼85pc and ∼280pc, respectively. In the inner
Galaxy, the molecular mass in the thin disk is dominant, while the
molecular mass traced by the discrete MCs with weak CO emission in the
thick disk is probably ≲10% of the whole molecular disk. For the CO
gas in the thick disk, we identified 1055 high-z MCs that are ≳100pc
from the Galactic plane. However, only a few samples (i.e., 32 MCs or
3%) are located in the |z|≳360pc region. Typically, the discrete MCs
of the thick-disk population have a median peak temperature of 2.1K, a
median velocity dispersion of 0.8km/s, and a median effective radius
of 2.5pc. Assuming a constant value of XCO=2x1020cm-2(K.km/s)-1,
the median surface density of these MCs is 6.8M☉/pc2,
indicating very faint CO emission for the high-z gas. The cloud-cloud
velocity dispersion is 4.9±1.3km/s and a linear variation with a
slope of ~-0.4km/s/kpc is obtained in the region of RGC=2.2-6.4kpc.
Assuming that these clouds are supported by their turbulent motions
against the gravitational pull of the disk, a model of
ρ0(R)=1.28M☉/pc3e-(R/3.2kpc) can be used to describe
the distribution of the total mass density in the Galactic midplane.
Description:
The Milky Way Imaging Scroll Painting (MWISP) project is an ongoing
large-scale, unbiased, and high-quality CO survey toward the northern
Galactic plane (e.g., see more details in Su+ 2019ApJS..240....9S 2019ApJS..240....9S).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 68 1055 Parameters of 1055 molecular clouds far from the
Galactic Plane based on the Milky Way Imaging
Scroll Painting (MWISP) 12CO(J=1-0) emission
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See also:
J/ApJ/688/290 : GASS HI survey of the lower halo (Ford+, 2008)
J/ApJ/722/367 : HI clouds in Quadrant I of the Milky Way (Ford+, 2010)
J/ApJ/723/492 : Physical properties of GRS MCs (Roman-Duval+, 2010)
J/AJ/146/150 : Velocity dispersions of 12 nearby gal. (Caldu-Primo+, 2013)
J/ApJ/798/L27 : CO obs. of molecular clouds in the 2nd quadrant (Sun+, 2015)
J/ApJS/224/7 : CO obs. of the outer arm in the 2nd quadrant (Du+, 2016)
J/ApJ/831/124 : Milky Way kinematics. II. (McClure-Griffiths+, 2016)
J/ApJ/828/59 : Molecular clouds in the Milky Way with CO obs. (Su+, 2016)
J/A+A/601/A124 : Clouds in SEDIGISM science demo. field (Schuller+, 2017)
J/ApJS/230/17 : CO obs. of MCs in Extreme Outer Galaxy region (Sun+, 2017)
J/ApJS/234/2 : The GALFA-HI survey data release 2 (Peek+, 2018)
J/MNRAS/483/4291 : Properties of JCMT CO(3-2) molecular clouds (Colombo+, 2019)
J/ApJ/885/131 : ∼200 high-mass SFR plx & PM with VLBI (Reid+, 2019)
J/A+A/633/A147 : FQS. Galactic Plane CO survey (Benedettini+, 2020)
J/ApJS/257/51 : Morph. classif. of MWISP 12CO mol. clouds (Yuan+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/1055] Running sequence number
6- 11 F6.3 deg GLON [16/52] Galactic longitude
13- 18 F6.3 deg GLAT [-5/4.6] Galactic latitude
20- 25 F6.2 km/s Vlsr [55.41/146.15] Local Standard of Rest velocity
27- 30 F4.2 km/s Sigma [0.35/4.82] One-dimensional velocity dispersion
(σv)
32- 36 F5.2 K Tpk [1/12.18] Peak emission
38- 43 F6.2 arcmin2 Area [1.25/242] Molecular cloud's area
45- 47 F3.1 kpc Dist [5/7.8] Distance (1)
49- 54 F6.1 pc Zsc [-590.1/606.8] z scale (z=d*tan(b))
56- 62 F7.1 Msun Mass [20/22090] Mass (2)
64- 68 F5.1 --- alpha [1.4/158.1] Virial parameter, α (3)
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Note (1): The MC's distance obtained from the tangent points,
i.e., d=R0*cos(l)
The error of the estimated distance is about 2%-20% from
l=16°-52° assuming that the MCs are located near tangent
points with a velocity uncertainty of ∼5km/s along the line of
sight (e.g., refer to the A5 model in Reid+ 2019, J/ApJ/885/131).
Note (2): The MC's mass estimated from the CO-to-H2 conversion factor method,
XCO=2x1020cm-2(K.km/s)-1 (e.g., Dame+ 2001ApJ...547..792D 2001ApJ...547..792D
and Bolatto+ 2013ARA&A..51..207B 2013ARA&A..51..207B).
Note (3): The MC's virial parameter
α=Mvirial/MXfactor=(5σv2R)/GMXfactor, where
R is the radius of the MC and G the gravitational constant.
See Section 3.3.1.
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Acknowledgements:
Yang Su [yangsu at pmo.ac.cn]
(End) Emmanuelle Perret [CDS] 20-Sep-2022