J/ApJ/680/349 Galactic distribution of IRDCs (Jackson+, 2008)
The galactic distribution of infrared dark clouds.
Jackson J.M., Finn S.C., Rathborne J.M., Chambers E.T., Simon R.
<Astrophys. J., 680, 349-361 (2008)>
=2008ApJ...680..349J 2008ApJ...680..349J
ADC_Keywords: Nebulae, dark ; Infrared sources
Keywords: Galaxy: structure - ISM: clouds - stars: formation
Abstract:
CS(2-1) measurements toward a large sample of fourth Galactic quadrant
infrared dark clouds (IRDCs) were made with the Australia Telescope
National Facility Mopra telescope in order to establish their
kinematic distances and Galactic distribution. Due to its large
critical density, CS unambiguously separates the dense IRDCs from more
diffuse giant molecular clouds. The fourth-quadrant IRDCs show a
pronounced peak in their radial galactocentric distribution at R=6kpc.
The first-quadrant IRDC distribution (traced by 13CO emission) also
shows a peak, but at a galactocentric radius of R=5kpc rather than
6kpc. The reliability of the MSX IRDC catalog by Simon and coworkers
is estimated by using the CS detection rate of IRDC candidates. The
overall reliability is at least 58%, and increases to near 100% for
high contrasts, Galactic longitudes within ∼30° of the Galactic
center, and large mid-IR backgrounds. A significant fraction of our
IRDC sample (14%) showed two CS velocity components, which probably
represent two distinct IRDCs along the same line of sight.
Description:
Observations were made using the 22m Australia Telescope National
Facility (ATNF) Mopra telescope. The first set of observations was
obtained 2005 June 15-18 and the second set was obtained 2006 April
30-May 3. To select our sample of fourth-quadrant IRDCs, we used the
catalog of IRDC candidates compiled by Simon et al. (2006, Cat.
J/ApJ/639/227).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 69 210 Fourth-quadrant IRDC cores detected in CS
table2.dat 33 134 Fourth-quadrant IRDC candidates not detected in CS
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See also:
J/MNRAS/313/641 : FAUST observations in 4th Galactic Quadrant (Brosch+, 2000)
J/ApJ/653/1325 : Galactic distribution of infrared dark clouds (Simon+, 2006)
J/ApJ/639/227 : MSX IRDC candidate catalog (Simon+, 2006)
J/ApJ/706/727 : Distance and mass of Infrared Dark Clouds (Marshall+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- MSXDC IRDC candidate name (GLLL.ll+BB.bb)
15 A1 --- m_MSXDC [abc] a to c core designation (G1)
17- 22 F6.2 deg GLON Galactic longitude coordinate
24- 28 F5.2 deg GLAT Galactic latitude coordinate
30- 33 F4.2 --- Peak Peak contrast (G2)
35- 38 F4.2 K TA*p Antenna temperature peak
40- 45 F6.1 km/s Vel Systemic velocity
47- 50 F4.1 km/s W(CS) CS(2-1) line width (97.981GHz)
52- 56 F5.2 K.km/s Int Integrated CS line intensity
58- 62 F5.2 kpc Rgal ? Galactocentric radius
64- 67 F4.2 kpc Dnear ? Near kinematic distance
69 A1 --- Comp [Y] two velocity components?
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- MSXDC Cloud name (GLLL.ll+BB.bb)
15 A1 --- m_MSXDC [ab] a to b core designation (G1)
17- 22 F6.2 deg GLON Galactic longitude coordinate
24- 28 F5.2 deg GLAT Galactic latitude coordinate
30- 33 F4.2 --- Peak Peak contrast (G2)
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Global notes:
Note (G1): We observed each IRDC candidate toward the darkest part of each
cloud (the position with the peak contrast), denoted in the MSX IRDC
catalog as "core a". In a few cases, a single IRDC candidate contains
two or three contrast peaks with values greater than our selection
criterion of contrasts larger than 32%. For these IRDC candidates, we
observed each contrast peak (subsequently called a core) separately.
Such positions are denoted as "cores b or c".
Note (G2): the contrast is defined in Simon et al. 2006,
Cat. J/ApJ/639/227 [(background-image)/background]
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 14-Oct-2010