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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 107 156 Molecular cloud catalog
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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
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Bytes Format Units Label Explanations
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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
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Note (1): Of GMC major axis, measured counter-clockwise from RA through DEC.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Sep-2017