J/ApJ/764/102 First quadrant IRDCs in CS(2-1) with Mopra (Finn+, 2013)
The distribution of infrared dark clouds in the first Galactic quadrant.
Finn S.C., Jackson J.M., Rathborne J.M., Chambers E.T., Simon R.
<Astrophys. J., 764, 102 (2013)>
=2013ApJ...764..102F 2013ApJ...764..102F
ADC_Keywords: Molecular clouds ; Radio lines ; Infrared sources ; Milky Way
Keywords: Galaxy: structure; ISM: clouds; stars: formation
Abstract:
Infrared dark clouds (IRDCs) are believed to host the earliest stages
of high-mass star and cluster formation. Because O stars typically
travel short distances over their lifetimes, if IRDCs host the
earliest stages of high-mass star formation then these cold, dense
molecular clouds should be located in or near the spiral arms in the
Galaxy. The Galactic distribution of a large sample of IRDCs should
therefore provide information on Galactic structure. Moreover,
determination of distances enables mass and luminosity calculations.
We have observed a large sample of IRDC candidates in the first
Galactic quadrant in the dense gas tracer CS(2-1) using the Mopra
telescope in order to determine kinematic distances from the molecular
line velocities. We find that the IRDCs are concentrated around a
Galactocentric distance of ∼4.5kpc, agreeing with the results of Simon
et al. (2006, J/ApJ/653/1325). This distribution is consistent with
the location of the Scutum-Centaurus spiral arm. The group of IRDCs
near the Sun in the first quadrant detected in 13CO(1-0) in Simon
et al. is not detected in the CS data. This discrepancy arises from
the differences in the critical densities between the 13CO(1-0) and
CS(2-1) lines. We determine that the Midcourse Space Experiment
selected IRDCs are not a homogeneous population, and 13CO(1-0)
traces a population of IRDCs with lower column densities and lower 1.1
mm flux densities in addition to more dense IRDCs detected in CS.
Masses of the first quadrant IRDCs are calculated from 13CO(1-0)
maps. We find a strong peak in the Galactocentric IRDC mass surface
density distribution at RGal∼4.5kpc.
Description:
We observed 272 IRDCs detected in 13CO(1-0) from Simon et al.
(2006, J/ApJ/653/1325) using the Australia Telescope National Facility
(ATNF) 22m Mopra telescope in Coonabarabran, New South Wales,
Australia. These observations took place from 2008 August 14 to 2008
August 24. The spectra have a velocity resolution of ∼0.1km/s at the
frequency of the CS(2-1) line, 97.98GHz.
We find distances to 189 IRDCs (170 detected IRDCs plus 19 additional
velocity component detections) assuming circular orbits about the
Galactic center and using the Clemens (1985ApJ...295..422C 1985ApJ...295..422C) rotation
curve for the Milky Way, with (R0, Θ0)=(8.5kpc, 220km/s).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 78 189 First quadrant IRDCs detected in CS(2-1) (97.98GHz)
table2.dat 36 102 13CO(1-0) clouds not detected in CS(2-1)
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See also:
II/293 : GLIMPSE Source Catalog (I + II + 3D) (IPAC 2008)
J/A+A/559/A79 : IRDC APEX/SABOCA observations (Ragan+, 2013)
J/ApJ/754/62 : HRDS III. HII region kinematic distances (Anderson+, 2012)
J/ApJ/721/137 : The Bolocam Galactic Plane Survey (BGPS) (Bally+, 2010)
J/MNRAS/399/1506 : IRDC cores in SCUBA Legacy Catalogue (Parsons+, 2009)
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)
J/ApJ/686/384 : 12CO, 13CO, C18O survey of IRDCs (Du+, 2008)
J/ApJ/680/349 : Galactic distribution of IRDCs (Jackson+, 2008)
J/ApJ/653/1325 : Galactic distribution of infrared dark clouds (Simon+, 2006)
J/ApJ/641/389 : Millimetric observations of IRDC cores (Rathborne+, 2006)
J/ApJ/639/227 : MSX IRDC candidate catalog (Simon+, 2006)
J/ApJ/566/945 : Massive star forming regions at 1.2mm (Beuther+, 2002)
J/A+A/358/257 : Molecular clouds SO and CS obs. II. (Nilsson+, 2000)
J/A+A/291/943 : Protostellar cores (Ossenkopf+, 1994)
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 MSXDC designation (GLLL.ll+BB.bb)
14 A1 --- m_MSXDC Cloud components
16- 20 F5.2 deg GLON Galactic longitude
22- 26 F5.2 deg GLAT Galactic latitude
28- 31 F4.2 K T*A [0.06/2.1] Antenna peak temperature
33- 38 F6.2 km/s V(CS) [9.2/113] CS velocity
40- 44 F5.2 km/s FWHM [0.5/16] CS line FWHM
46- 50 F5.2 K.km/s Int [0.1/13.2] Integrated intensity
52- 54 F3.1 kpc Rgal [3.5/8] Galactocentric radius
56- 58 F3.1 kpc Dnear [0.8/8] Kinematic distance (Dnear)
60- 64 I5 Msun Mass [20/57970] LTE mass from 13CO(1-0) maps
66 I1 --- Nv [1/3] Number of velocity components in the
spectrum for the source
68- 72 F5.1 km/s V(CO) ? 13CO velocity (1)
73 A1 --- f_V(CO) [*] Mismatch in CO and CS velocities (1)
75- 78 F4.1 10+21/cm2 NH2 [2.4/37] Peak H2 column density (2)
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Note (1): An asterisk marks where the 13CO velocity differs from the CS
velocity by more than 3.3km/s. Blanks indicate second and third CS
velocity components where only one 13CO velocity was identified.
Note (2): Reported column densities are from Simon et al. 2006
(J/ApJ/653/1325) except in the cases where the CS velocity differed
from the 13CO velocity by more than 3.3km/s or for a new velocity
component. See Section 3.3.2 for details.
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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 MSXDC designation (GLLL.ll+BB.bba)
14 A1 --- m_MSXDC Cloud components
16- 20 F5.2 deg GLON Galactic longitude
22- 26 F5.2 deg GLAT Galactic latitude
28- 31 F4.2 K rms [0.07/0.3] rms noise of T*A
33- 36 F4.1 10+21/cm2 NH2 [0.1/17] Peak H2 column density (1)
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Note (1): These column densities are from Simon et al. 2006 (J/ApJ/653/1325)
based on the 13CO(1-0) detections.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 27-Oct-2014