J/ApJ/706/727 Distance and mass of Infrared Dark Clouds (Marshall+, 2009)
Distribution and characteristics of infrared dark clouds using genetic forward
modelling.
Marshall D.J., Joncas G., Jones A.P.
<Astrophys. J., 706, 727-737 (2009)>
=2009ApJ...706..727M 2009ApJ...706..727M
ADC_Keywords: Molecular clouds; Infrared sources ; Morphology
Keywords: dust, extinction - Galaxy: structure
Abstract:
Infrared Dark Clouds (IRDCs) are dark clouds seen in silhouette in
mid-infrared surveys. They are thought to be the birthplace of massive
stars, yet remarkably little information exists on the properties of
the population as a whole (e.g., mass spectrum, spatial distribution).
Genetic forward modeling is used along with the Two Micron All Sky
Survey and the Besancon Galactic model to deduce the three-dimensional
distribution of interstellar extinction toward previously identified
IRDC candidates. This derived dust distribution can then be used to
determine the distance and mass of IRDCs, independently of kinematic
models of the Milky Way. Along a line of sight that crosses an IRDC,
the extinction is seen to rise sharply at the distance of the cloud.
Assuming a dust-to-gas ratio, the total mass of the cloud can be
estimated. The method has been successfully applied to 1259 IRDCs,
including over 1000 for which no distance or mass estimate currently
exists. The IRDCs are seen to lie preferentially along the spiral arms
and in the molecular ring of the Milky Way, reinforcing the idea that
they are the birthplace of massive stars. Also, their mass spectrum is
seen to follow a power law with an index of -1.75±0.06, steeper than
giant molecular clouds (GMCs) in the inner Galaxy but comparable to
clumps in GMCs. This slope suggests that the IRDCs detected using the
present method are not gravitationally bound, but are rather the
result of density fluctuations induced by turbulence.
Description:
For each cloud, its name, Galactic coordinates l and b, distance,
extinction, size, mass, the number of 2MASS stars used in extinction
calculation, the reduced chi-squared, and the number of standard
deviations the density of the cloud sits above the background are
listed in order.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
irdc.dat 80 1218 Results for the Infra-Red Dark Cloud (IRDC)
characteristics (table1 of the paper)
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/ApJS/95/457 : IRAS images of nearby dark clouds (Wood+ 1994)
J/ApJS/166/567 : Radio Molecular lines in infrared dark clouds (Ragan+, 2006)
J/ApJ/653/1325 : Galactic distribution of infrared dark clouds (Simon+, 2006)
J/ApJ/651/L125 : Water masers associated with IR dark cloud cores (Wang+ 2006)
J/ApJ/641/389 : Millimetric observations of IRDC cores (Rathborne+, 2006)
J/ApJ/639/227 : MSX IRDC candidate catalog (Simon+, 2006)
J/A+A/505/405 : A catalogue of Spitzer dark clouds (Peretto+, 2009)
J/A+A/499/149 : 1.2mm maps of southern Infrared Dark Clouds (Vasyunina+ 2009)
Byte-by-byte Description of file: irdc.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- MSXDC IRDC Name (GLLL.ll+BB.bbb) (1)
16- 23 F8.4 deg Glon Galactic Longitude
27- 33 F7.4 deg Glat Galactic Latitude
36- 40 F5.2 kpc Dist Distance to IRDC
43- 47 F5.3 mag AKs Ks band extinction of IRDC
50- 54 F5.2 pc Size Size of IRDC
56- 60 I5 solMass Mass Mass of IRDC
63- 66 I4 --- Nobs Number of 2MASS stars used in calculation
70- 73 F4.2 --- chi2r Reduced chi squared of J-K histogram fit (2)
75- 80 F6.2 --- sigma Standard deviation above diffuse extinction
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Note (1): From Simon et al., 2006, Cat. J/ApJ/639/227.
Note (2): Between Galactic model, corrected for extinction, and observations.
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Acknowledgements:
Douglas Marshall, douglas.marshall(at)cesr.fr
(End) Patricia Vannier [CDS] 11-Jan-2010