J/ApJ/686/384 12CO, 13CO, C18O survey of IRDCs (Du+, 2008)
A 12CO, 13CO, and C18O survey of infrared dark clouds.
Du F., Yang J.
<Astrophys. J., 686, 384-398 (2008)>
=2008ApJ...686..384D 2008ApJ...686..384D
ADC_Keywords: Molecular clouds ; Interstellar medium ; Infrared sources ;
Radio lines
Keywords: dust, extinction - Galaxy: structure - infrared: ISM -
radio lines: ISM - stars: formation
Abstract:
Infrared dark clouds (IRDCs) are extinction features against the
Galactic infrared background, mainly in the mid-infrared band.
Recently they were proposed to be potential sites of massive star
formation. In this work we have made a 12CO, 13CO, and C18O
(J=1->0) survey of 61 IRDCs, 52 of which are in the first Galactic
quadrant, selected from a catalog given by Simon and coworkers (2006,
Cat. J/ApJ/639/227), while the others are in the outer Galaxy,
selected by visually inspecting the Midcourse Space Experiment (MSX)
images. Detection rates in the three CO lines are 90%, 71%, and 62%,
respectively. The distribution of IRDCs in the first Galactic quadrant
is consistent with the 5kpc molecular ring picture, while a slight
trace of a spiral pattern is also noticeable, and needs to be further
examined. The IRDCs have a typical excitation temperature of 10K and
typical column density of several 1022cm-2. Their typical
physical size is estimated to be several parsecs using angular sizes
from the Simon catalog.
Description:
Our observations were taken during the observation season between 2006
and 2007 with the 13.7m radio telescope in Delingha, China, which is
operated by Purple Mountain Observatory.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 51 61 List of source names, galactic coordinates, and
equatorial coordinates
table3.dat 105 83 Observed properties of the IRDCs
table4.dat 79 61 Physical parameters of the IRDCs
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See also:
J/ApJ/639/227 : MSX IRDC candidate catalog (Simon+, 2006)
J/ApJ/653/1325 : Galactic distribution of infrared dark clouds (Simon+, 2006)
J/ApJS/166/567 : Radio Molecular lines in infrared dark clouds (Ragan+, 2006)
J/ApJ/641/389 : Millimetric observations of IRDC cores (Rathborne+, 2006)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Running sequence number
4- 16 A13 --- MSXDC Source name (GLLL.ll+BB.bb)
17 A1 --- n_MSXDC [ab] Adopted peak: first (a) or second (b)
19- 25 F7.3 deg GLON Galactic longitude coordinate
27- 32 F6.3 deg GLAT Galactic latitude coordinate
34- 35 I2 h RAh Hour of right ascension (J2000)
37- 38 I2 min RAm Minute of right ascension (J2000)
40- 41 I2 s RAs Second of right ascension (J2000)
43 A1 --- DE- Declination sign (J2000)
44- 45 I2 deg DEd Degree of declination (J2000)
47- 48 I2 arcmin DEm Arcminute of declination (J2000)
50- 51 I2 arcsec DEs Arcsecond of declination (J2000)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Running sequence number
3 A1 --- m_Seq Multiple component of the same source (1)
5- 17 A13 --- MSXDC Name (GLLL.ll+BB.bb)
19- 23 F5.2 K TR12 ? 12CO radiation temperature T*R
25- 30 F6.2 K.km/s Int12 ? 12CO integrated intensity
32- 37 F6.2 km/s Vlsr12 ? 12CO local standard of rest (LSR) velocity
39- 43 F5.2 km/s dV12 ? 12CO line width
45- 48 F4.2 K e_TR12 ? TR12 uncertainty
50- 54 F5.2 K TR13 ? 13CO radiation temperature T*R
56- 60 F5.2 K.km/s Int13 ? 13CO integrated intensity
62- 67 F6.2 km/s Vlsr13 ? 13CO local standard of rest (LSR) velocity
69- 72 F4.2 km/s dV13 ? 13CO line width
74- 77 F4.2 K e_TR13 ? TR13 uncertainty
79- 82 F4.2 K TR18 ? C18O radiation temperature T*R
84- 88 F5.2 K.km/s Int18 ? C18O integrated intensity
90- 95 F6.2 km/s Vlsr18 ? C18O local standard of rest (LSR) velocity
97-100 F4.2 km/s dV18 ? C18O line width
102-105 F4.2 K e_TR18 ? TR18 uncertainty
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Note (1): Sources with multiple components are marked with numbers appended
with letters a, b, c in descending order of C18O optical depth if it
is detected, otherwise in descending order of optical depth of 13CO
or intensity of 12CO.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Running sequence number
4- 16 A13 --- MSXDC Name (GLLL.ll+BB.bb) (1)
18- 22 F5.2 K Texc ? Excitation temperature (2)
24- 28 F5.2 kpc Dist ? Heliocentric distance (3)
30- 34 F5.2 pc Size ? Size (4)
36- 39 F4.2 --- tau13 ? 13CO optical depth
41- 44 F4.2 10+22/cm2 NH2.13 ? H2 column density with 13CO (5)
46- 50 I5 cm-3 nH2.13 ? H2 volume density with 13CO (5)
52- 56 I5 Msun M13 ? Mass with 13CO (5)
58- 61 F4.2 --- tau18 ? C18O optical depth
63- 66 F4.2 10+22/cm2 NH218 ? H2 column density with C18O (5)
68- 72 I5 cm-3 nH2.18 ? H2 volume density with C18O (5)
74- 79 I6 Msun M18 ? Mass with C18O (5)
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Note (1): For sources with multiple components, the first components in Table 3
are used to derive the physical parameters.
Note (2): The excitation temperatures are derived from the peak 12CO
temperature; for sources with apparent self-absorption, the values
derived this way may be unreliable.
Note (3): The distance of each source is derived from the LSR velocity using a
Galactic rotation curve model given by Fich et al.
(1989ApJ...342..272F 1989ApJ...342..272F).
Note (4): Following Simon et al. (2006, Cat. J/ApJ/653/1325), the source sizes
are calculated using the kinematic distances derived here and the
major and minor axis lengths in the Simon catalog. For sources in the
outer galaxy, their angular sizes are estimated from the MSX images.
Note (5): The column densities of H2 are derived assuming a simple LTE model,
with a moderate 13CO abundance of 1x10-6, and C18O abundance of
1.4x10-7 (Dickman 1978ApJS...37..407D 1978ApJS...37..407D; Burgh et al.
2007ApJ...658..446B 2007ApJ...658..446B; Kramer et al. 1999A&A...342..257K 1999A&A...342..257K; Frerking et
al. 1982ApJ...262..590F 1982ApJ...262..590F). The volume densities are derived by simply
dividing the column densities by the sizes, and the masses are just
the products of column densities and areas.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 04-Jan-2011