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J/ApJ/835/278   Molecular clouds in the dwarf galaxy NGC6822   (Schruba+, 2017)

Physical properties of molecular clouds at 2pc resolution in the low-metallicity dwarf galaxy NGC 6822 and the Milky Way. Schruba A., Leroy A.K., Kruijssen J.M.D., Bigiel F., Bolatto A.D., de Blok W.J.G., Tacconi L., van Dishoeck E.F., Walter F. <Astrophys. J., 835, 278-278 (2017)> =2017ApJ...835..278S (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Millimetric/submm sources ; Galaxies, nearby ; Carbon monoxide Keywords: galaxies: individual: NGC 6822; H II regions; ISM: clouds; radio lines: ISM Abstract: We present the Atacama Large Millimeter/submillimeter Array survey of CO(2-1) emission from the 1/5 solar metallicity, Local Group dwarf galaxy NGC 6822. We achieve high (0.9"∼2pc) spatial resolution while covering a large area: four 250pcx250pc regions that encompass ∼2/3 of NGC 6822's star formation. In these regions, we resolve ∼150 compact CO clumps that have small radii (∼2-3pc), narrow line width (∼1km/s), and low filling factor across the galaxy. This is consistent with other recent studies of low-metallicity galaxies, but here shown with a 15x larger sample. At parsec scales, CO emission correlates with 8µm emission better than with 24µm emission and anticorrelates with Hα, so that polycyclic aromatic hydrocarbon emission may be an effective tracer of molecular gas at low metallicity. The properties of the CO clumps resemble those of similar-size structures in Galactic clouds except of slightly lower surface brightness and with CO-to-H2 ratio ∼1-2x the Galactic value. The clumps exist inside larger atomic-molecular complexes with masses typical for giant molecular clouds. Using dust to trace H2 for the entire complex, we find the CO-to-H2 ratio to be ∼20-25x the Galactic value, but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state. The H2-to-HI ratio is low globally and only mildly above unity within the complexes. The ratio of star formation rate to H2 is ∼3-5x higher in the complexes than in massive disk galaxies, but after accounting for the bias from targeting star-forming regions, we conclude that the global molecular gas depletion time may be as long as in massive disk galaxies. Description: We observed five fields in NGC 6822 with the Atacama Large Millimeter/submillimeter Array (ALMA) in Cycle 1 using the 1.3mm Band 6 receivers (project code: 2013.1.00351.S; PI. A. Schruba) in 2014 Mar 23-25. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table6.dat 107 156 Molecular cloud catalog
See also: J/AJ/121/2020 : CTIO and WFPC2 photometry in NGC 6822 (Bianchi+, 2001) J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001) J/ApJS/144/47 : Outer galaxy molecular cloud catalog (Brunt+, 2003) J/AJ/128/16 : HIPASS Bright Galaxy Catalog (Koribalski+, 2004) J/AJ/132/378 : HST and UV photometry of NGC 6822 (Bianchi+, 2006) J/A+A/462/L17 : Dense cores in interstellar molecular clouds (Alves+, 2007) J/ApJS/178/56 : CO observations of LMC Giant Molecular clouds (Fukui+, 2008) J/ApJ/699/742 : Properties of cores in the Pipe Nebula (Rathborne+, 2009) J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010) J/AJ/141/23 : HI holes in THINGS galaxies (Bagetakos+, 2011) J/ApJS/196/18 : CO survey of galactic molecular clouds. II. (Bieging+, 2011) J/ApJ/730/88 : Star-forming regions in NGC 6822 from UV (Efremova+, 2011) J/ApJS/197/16 : CO observations of LMC molecular clouds (MAGMA). (Wong+, 2011) J/AJ/143/74 : HST photometry in 6 dwarf galaxies (Bianchi+, 2012) J/AJ/143/133 : Dwarf galaxies from the ALFALFA survey (Huang+, 2012) J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012) J/ApJ/774/73 : ALMA CO observations of 30 Dor (Indebetouw+, 2013) J/ApJ/794/107 : Distance to NGC6822 with Spitzer/FourStar data (Rich+, 2014) J/A+A/580/A112 : THOR. The HI, OH, Recombination Line Survey (Bihr+, 2015) J/ApJ/813/42 : O and B type stars in W3: first results (Kiminki+, 2015) J/A+A/582/A121 : Dust properties in galaxies (Remy-Ruyer+, 2015) Byte-by-byte Description of file: table6.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Seq GMC running sequence number 5- 6 I2 h RAh [19] Hour of Right Ascension (J2000) 8- 9 I2 min RAm [44/45] Minute of Right Ascension (J2000) 11- 14 F4.1 s RAs Second of Right Ascension (J2000) 16 A1 --- DE- [-] Sign of the Declination (J2000) 17- 18 I2 deg DEd [14] Degree of Declination (J2000) 20- 21 I2 arcmin DEm [41/53] Arcminute of Declination (J2000) 23- 24 I2 arcsec DEs Arcsecond of Declination (J2000) 26- 30 F5.1 km/s VLSR [-73/-26] Local Standard of Rest velocity 32- 35 F4.1 K Tpk [0.7/15] Peak brightness temperature 37- 40 F4.1 --- S/N [2/33] Peak signal-to-noise ratio 42- 45 F4.1 pc Rmaj [0.9/12]? Major Axis Radius 47- 50 F4.1 pc Rmin [0.2/5]? Minor Axis Radius 52- 55 I4 deg PA ? Position Angle (1) 57- 60 F4.1 pc Rad [0.1/8]? Radius 62- 65 F4.1 pc e_Rad [0.1/3]? Uncertainty in Rad 67- 70 F4.2 km/s sigV [0.1/3]? Velocity dispersion 72- 75 F4.2 km/s e_sigV [0/2]? Uncertainty in sigV 77- 80 F4.1 10+2K.km/s.pc2 LCO [0/9] CO luminosity 82- 85 F4.1 10+2K.km/s.pc2 e_LCO [0/7] Uncertainty in LCO 87- 91 F5.1 10+2Msun Mvir [0.2/531]? Mass from virial theorem 93- 97 F5.1 10+2Msun e_Mvir [0/229]? Uncertainty in Mvir 99-102 F4.1 --- alpha [0.5/84]? Virial parameter (ratio of virial to luminous mass) 104-107 F4.1 --- e_alpha [0.2/38]? Uncertainty in alpha
Note (1): Of GMC major axis, measured counter-clockwise from RA through DEC.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Sep-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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