J/A+A/552/A40 MSX high-contrast IRDCs with NH3 (Chira+, 2013)
Characterization of infrared dark clouds.
NH3 observations of an absorption-contrast selected IRDC sample.
Chira R.-A., Beuther H., Linz H., Walmsley C. M., Menten, K.M., Bonfman L.
<Astron. Astrophys. 552, A40 (2013)>
=2013A&A...552A..40C 2013A&A...552A..40C
ADC_Keywords: Galactic plane ; Interstellar medium ; Radial velocities;
Spectra, millimetric/submm ; Abundances ; Surveys
Keywords: stars: formation - IMF: clouds - IMF: molecules - IMF: abundances
Abstract:
Despite increasing research in massive star formation, little is known
about its earliest stages. Infrared Dark Clouds (IRDCs) are cold,
dense and massive enough to harbour the sites of future high-mass star
formation. But up to now, mainly small samples have been observed and
analysed.
To understand the physical conditions during the early stages of
high-mass star formation, it is necessary to learn more about the
physical conditions and stability in relatively unevolved IRDCs. Thus,
for characterising IRDCs studies of large samples are needed.
We investigate a complete sample of 220 northern hemisphere
high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion
transitions.
We detected ammonia (1,1)-inversion transition lines in 109 of our
IRDC candidates. Using the data we were able to study the physical
conditions within the star-forming regions statistically. We compared
them with the conditions in more evolved regions which have been
observed in the same fashion as our sample sources. Our results show
that IRDCs have, on average, rotation temperatures of 15K, are
turbulent (with line width FWHMs around 2km/s), have ammonia column
densities on the order of 1014cm-2 and molecular hydrogen column
densities on the order of 1022cm-2. Their virial masses are
between 100 and a few 1000M☉. The comparison of bulk kinetic and
potential energies indicate that the sources are close to virial
equilibrium.
IRDCs are on average cooler and less turbulent than a comparison
sample of high-mass protostellar objects, and have lower ammonia
column densities. Virial parameters indicate that the majority of
IRDCs are currently stable, but are expected to collapse in the
future.
Description:
Based on MSX data, a catalogue of more than 10,000 candidate IRDCs was
compiled. From this catalogue we selected a complete sample of
northern hemisphere high-contrast IRDCs with Galactic longitudes
≥19.27° (and nine exceptions with Galactic longitudes <19°).
The sample was observed in ammonia (1,1) and (2,2) inversion
transitions with the Effelsberg 100-m telescope. NH3 parameters are
derived for 109 sample sources. For each source galactic coordinates,
brightness temperatures, line width FWHMs and optical depths of (1,1)
and (2,2) inversion lines and LSR velocity of (1,1) inversion line are
given. Furthermore, we derived the rotation and kinetic temperatures,
ammonia column densities, kinematic distances and virial masses using
the NH3 data. In addition, notes about whether the sources being
associated with Spitzer sources or not are given. Using ATLASGAL data,
the 870 micron flux densities gas masses, virial parameters, H2
column densities and NH3 abundances are given. In addition, we
listed the sample sources where no ammonia which did not fulfil our
selection criteria.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 90 109 Source position, NH3(1,1) line parameters
and NH3(2,2) line brightness temperature,
line width and optical depth
tablec2.dat 72 109 Parameters obtained from NH3 lines and
note about Spitzer association
tablec3.dat 92 100 Parameters obtained with 870 micron dust
continuum, in combination with NH3 data
tablec4.dat 27 109 List of sources without detected ammonia
(1,1) inversion lines
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See also:
J/ApJ/639/227 : MSX IRDC candidate catalog (Simon+, 2006)
J/A+A/540/A113 : Starless clumps in ATLASGAL (Tackenberg+, 2012)
J/A+A/544/A146 : ATLASGAL cold high-mass clumps with NH3 (Wienen+, 2012)
J/MNRAS/431/1752 : ATLASGAL 6.7GHz methanol masers (Urquhart+, 2013)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name MSX-IRDC source name (GLLL.ll+BB.bbA)
16- 20 F5.2 deg GLON Galactic Longitude
23- 27 F5.2 deg GLAT Galactic Latitude
30- 32 F3.1 K Tmb(1,1) NH3(1,1) main beam brightness temperature
35- 37 F3.1 K e_Tmb(1,1) rms uncertainty on Tmb(1,1)
40- 42 F3.1 K Tmb(2,2) NH3(2,2) main beam brightness temperature
45- 47 F3.1 K e_Tmb(2,2) rms uncertainty on Tmb(2,2)
50- 52 F3.1 km/s dv(1,1) NH3(1,1) line width FWHM
55- 57 F3.1 km/s dv(2,2) NH3(2,2) line width FWHM
60- 64 F5.1 km/s vlsr(1,1) LSR velocity of NH3(1,1) inversion line
67- 70 F4.2 --- tau(1,1) Optical depth τ of NH3(1,1) line
73- 76 F4.2 --- e_tau(1,1) rms uncertainty on tau(1,1)
79- 83 F5.2 --- tau(2,2) Optical depth of τ NH3(2,2) line
86- 90 F5.2 --- e_tau(2,2) rms uncertainty on tau(2,2)
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name MSX-IRDC source name (GLLL.ll+BB.bbA)
16- 19 F4.1 K Trot Rotation Temperature between NH3(1,1)
and (2,2) inversion line
22- 25 F4.1 K e_Trot rms uncertainty on Trot
28- 31 F4.1 K Tkin Kinetic Temperature
34- 36 F3.1 10+15cm-2 NNH3 NH3 column density
39- 41 F3.1 kpc Dist (near) kinematic distance
44- 46 F3.1 kpc e_Dist rms uncertainty on dist
49- 52 I4 Msun Mvir-1 virial mass by assuming a r-1 density profile
55- 57 I3 Msun e_Mvir-1 rms uncertainty on Mvir-1
60- 62 I3 Msun Mvir-2 virial mass by assuming a r-2 density profile
65- 67 I3 Msun e_Mvir-2 rms uncertainty on Mvir-2
70- 72 A3 --- Spitzer [yes/no ] note whether source has a Spitzer
24um counterpart ("yes") or not ("no")
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Byte-by-byte Description of file: tablec3.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name MSX-IRDC source name (GLLL.ll+BB.bbA)
16- 19 F4.2 Jy F19 870 micron dust continuum flux density
integrated over 19"
22- 25 F4.2 Jy F40 870 micron dust continuum flux density
integrated over 40"
28- 31 F4.1 10+22cm-2 NH2+19 H2 column density averaged on 19" beam
34- 37 F4.1 10+22cm-2 NH2+40 H2 column density averaged on 40" beam
40- 42 F3.1 10-8 chiNH3 NH3 abundance (κ=1.85cm2/g)
45- 48 I4 Msun M.OH gas mass Mgas using κ=1.85cm2/g (1)
51- 54 I4 Msun e_M.OH rms uncertainty on MOH
57- 60 I4 Msun M.MRN gas mass Mgas using κ=0.6cm2/g (1)
63- 66 I4 Msun e_M.MRN rms uncertainty on MMRN
69- 73 F5.1 --- al.OH virial parameter α using
κ=1.85cm2/g (1)
76- 80 F5.1 --- e_al.OH rms uncertainty on al.OH
83- 86 F4.1 --- al.MRN virial parameter α using
κ=0.6cm2/g (1)
89- 92 F4.1 --- e_al.MRN rms uncertainty on al.MRN
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Note (1): the virial parameter for molecular clouds is defined as
α=2Ekin/Epot=Mvir/Mgas (α=1 for equilibrium,
α>1 indicates an expanding cloud, α<1 a collapsing cloud).
OH refers of the Ossenkopf & Henning model (1994A&A...291..943O 1994A&A...291..943O), dust
absorption coefficient κν=1.85cm2/g, and MRN refers to
the Mathis et al. model (1977ApJ...217..425M 1977ApJ...217..425M), dust absorption
coefficient κν=0.6cm2/g.
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Byte-by-byte Description of file: tablec4.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name MSX-IRDC source name (GLLL.ll+BB.bbA)
16- 20 F5.2 deg GLON Galactic Longitude
23- 27 F5.2 deg GLAT Galactic Latitude
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Acknowledgements:
Roxana-Adela Chira, rox.chira(at)gmail.com
References:
Simon et al., 2006ApJ...639..227S 2006ApJ...639..227S, A Catalog of Midcourse Space Experiment
Infrared Dark Cloud Candidates (Cat. J/ApJ/639/227)
Schuller et al., 2009arXiv0903.1369S 2009arXiv0903.1369S, ATLASGAL-The APEX telescope large area
survey of the galaxy at 870 micron
(End) Patricia Vanner [CDS] 21-Feb-2013