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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
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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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?
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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)
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
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