J/ApJS/224/7 CO obs. of the outer arm in the 2nd quadrant (Du+, 2016)
An outer arm in the second galactic quadrant: structure.
Du X., Xu Y., Yang J., Sun Y., Li F., Zhang S., Zhou X.
<Astrophys. J. Suppl. Ser., 224, 7 (2016)>
=2016ApJS..224....7D 2016ApJS..224....7D (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Molecular clouds ; Interstellar medium ; Radio lines
Keywords: catalogs; Galaxy: structure; ISM: clouds; ISM: molecules
Abstract:
The lack of arm tracers, especially remote tracers, is one of the most
difficult problems preventing us from studying the structure of the
Milky Way. Fortunately, with its high-sensitivity CO survey, the Milky
Way Imaging Scroll Painting (MWISP) project offers such an
opportunity. Since completing about one-third of its mission, an area
of l=[100,150]°, b=[-3,5]° has nearly been covered. The Outer
arm of the Milky Way first clearly revealed its shape in the second
galactic quadrant in the form of molecular gas --this is the first
time that the Outer arm has been reported in such a large-scale
mapping of molecular gas. Using the 115GHz 12CO(1-0) data of MWISP
at the LSR velocity ~[-100,-60]km/s and in the area mentioned above,
we have detected 481 molecular clouds in total, and among them 332
(about 69%) are newly detected and 457 probably belong to the Outer
arm. The total mass of the detected Outer arm clouds is
∼3.1x106M☉_. Assuming that the spiral arm is a logarithmic
spiral, the pitch angle is fitted as ∼13.1°. Besides combining
both the CO data from MWISP and the 21cm HI data from the Canadian
Galactic Plane Survey (CGPS), the gas distribution, warp, and
thickness of the Outer arm are also studied.
Description:
The 12CO(1-0), 13CO(1-0), and C18O(1-0) lines were observed
simultaneously using the Purple Mountain Observatory Delingha 13.7m
telescope from 2011 September to 2015 March as one of the scientific
demonstration regions for the Milky Way Imaging Scroll Painting
(MWISP) project.
The 21cm line data were retrieved from the Canadian Galactic Plane
Survey (CGPS; Taylor et al. 2003, VI/128). We downloaded data of
l=[63,155]°, b=[-3,5]° from the Canadian Astronomy Data
Centre (http://cadc.hia.nrc.ca/).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 89 481 Parameters of molecular clouds derived by CO(1-0)
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See also:
VI/128 : Log of CGPS exposures (Taylor+, 2003-)
VIII/39 : Composite CO Survey of the Milky Way (Dame+ 1987)
J/ApJ/798/L27 : CO obs. of molecular clouds in the 2nd quadrant (Sun+, 2015)
J/A+A/569/A125 : Spiral structure of the Milky Way (Hou+, 2014)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/A+A/470/161 : UBV photometry of HII regions exciting stars (Russeil+, 2007)
J/ApJS/144/47 : Outer galaxy molecular cloud catalog (Brunt+, 2003)
J/A+A/397/133 : Star-forming complexes in the Galaxy (Russeil+, 2003)
J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)
J/ApJS/100/125 : CO(J=2-1) Survey of the Milky Way (Sakamoto+, 1995)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- --- [MWISP]
7- 21 A15 --- MWISP MWISP project source identifier (1)
23- 27 F5.1 km/s VLSR [-97/-47] Local Standard of Rest velocity (2)
29- 32 F4.1 K Tpeak [1/16.5] Peak temperature (2)
34- 36 F3.1 km/s DeltaV [0.4/5] Line width (2)
38- 41 F4.1 K.km/s ICO [1/51] CO line intensity (2)
43- 47 F5.1 arcmin2 Area [1.9/616.5] Solid angle defined by
the 3σ limit
49- 51 F3.1 kpc Dist [4.7/9] Heliocentric distance (3)
53- 56 F4.1 kpc Rad [12/16.7] Galactocentric radius (3)
58- 61 F4.1 pc Size [2/63.5] Equivalent cloud diameter (4)
63- 67 F5.1 10+3Msun Mass [0.1/620] Mass Cloud mass (5)
69- 72 F4.1 kpc Z [-0.1/0.7] Galactic scale height (Dist*sin(b))
74- 89 A16 --- Note Additional notes or identifiers (6)
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Note (1): In Galactic coordinates of Tpeak position.
Note (2): From Gaussian fit to the spectra.
Note (3): Derived by galactic parameters obtained by
Reid et al. (2014, J/ApJ/783/130).
Note (4): Corrected by the beam size of the telescope.
Note (5): Calculated by X=1.8x1020cm-2(K.km/s)-1
(Dame et al. 2001ApJ...547..792D 2001ApJ...547..792D).
Note (6): Identifiers as follows:
BW94 = sources detected by Brand & Wouterloot (1994A&AS..103..503B 1994A&AS..103..503B);
HCS01 = sources detected by Heyer et al. (2001, J/ApJ/551/852;
<[HCS2001] NNNNN> in Simbad);
BKP03 = sources detected by Brunt et al. (2003, J/ApJS/144/47;
<[BKP2003] NNNNN> in Simbad);
New Arm = clouds supposed to belong to the new spiral arm detected by
Sun et al. (2015, J/ApJ/798/L27; <[SXY2015] NN> in Simbad).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-Jun-2016