J/ApJ/715/310 Early stages of star formation in IRDCs (Rathborne+, 2010)
The early stages of star formation in infrared dark clouds:
characterizing the core dust properties.
Rathborne J.M., Jackson J.M., Chambers E.T., Stojimirovic I., Simon R.,
Shipman R., Frieswijk W.
<Astrophys. J., 715, 310-322 (2010)>
=2010ApJ...715..310R 2010ApJ...715..310R
ADC_Keywords: Molecular clouds ; Interstellar medium ; Infrared sources ;
Millimetric/submm sources
Keywords: dust, extinction - infrared: stars - stars: formation -
submillimeter: general
Abstract:
Identified as extinction features against the bright Galactic
mid-infrared background, infrared dark clouds (IRDCs) are thought to
harbor the very earliest stages of star and cluster formation. In
order to better characterize the properties of their embedded cores,
we have obtained new 24um, 60-100um, and submillimeter continuum data
toward a sample of 38 IRDCs. The 24um Spitzer images reveal that while
the IRDCs remain dark, many of the cores are associated with bright
24um emission sources, which suggests that they contain one or more
embedded protostars. Combining the 24um, 60-100um, and submillimeter
continuum data, we have constructed broadband spectral energy
distributions (SEDs) for 157 of the cores within these IRDCs and,
using simple graybody fits to the SEDs, have estimated their dust
temperatures, emissivities, opacities, bolometric luminosities,
masses, and densities. Based on their Spitzer/Infrared Array Camera
3-8um colors and the presence of 24um point-source emission, we have
separated cores that harbor active, high-mass star formation from
cores that are quiescent. The active "protostellar" cores typically
have warmer dust temperatures and higher bolometric luminosities than
the more quiescent, perhaps "pre-protostellar," cores. Because the
mass distributions of the populations are similar, however, we
speculate that the active and quiescent cores may represent different
evolutionary stages of the same underlying population of cores.
Although we cannot rule out low-mass star formation in the quiescent
cores, the most massive of them are excellent candidates for the
"high-mass starless core" phase, the very earliest in the formation of
a high-mass star.
Description:
The source list for these observations comprise 38 IRDCs and the 190
cores identified within them (Rathborne et al. 2006, Cat.
J/ApJ/641/389). To characterize the emission from these IRDCs and
their cores, we have obtained continuum data at many wavelengths with
Spitzer/MIPS, the Caltech Submillimeter Observatory (CSO), the James
Clerk Maxwell Telescope (JCMT), in addition to the 1.2mm observations
of Rathborne+:
----------------------------------------------------------------------
Telescope Inst Wavelength Observing dates Angular 1σ
Res noise
----------------------------------------------------------------------
Spitzer 0.85m MIPS 24um 2004/10,2005/04 6" ∼150uJy
Spitzer 0.85m SED-mode 60-100um 2006/10, 2007/05 13"-24" ∼100mJy
CSO 10m SHARC-2 350,450um 2005/09-04, 2006/04 8" ∼200mJy
JCMT 15m SCUBA 450,850um 2004/09 8",15" ∼60mJy
IRAM 30m MAMBO-II 1.2mm 2004/02 11" ∼10 mJy
----------------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 109 190 Core coordinates, distances, and measured fluxes
table3.dat 62 100 Properties of the cores derived from gray-body
fits to their broadband SEDs
table4.dat 78 57 Properties of the cores for which limits where
estimated from the gray-body fits to their
broadband SEDs
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See also:
V/114 : MSX6C Infrared Point Source Catalog (Egan+ 2003)
J/ApJ/639/227 : MSX IRDC candidate catalog (Simon+, 2006)
J/A+A/481/345 : SED evolution in massive YSOs (Molinari+, 2008)
J/ApJ/641/389 : Millimetric observations of IRDC cores (Rathborne+, 2006)
J/ApJ/653/1325 : Galactic distribution of infrared dark clouds (Simon+, 2006)
J/ApJ/651/L125 : Water masers associated with IRDC cores (Wang+, 2006)
J/ApJ/639/227 : MSX IRDC candidate catalog (Simon+, 2006)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- MSXDC The IRDC core identification (GLLL.ll+DD.dd MMNN)
20- 21 I2 h RAh Hour of Right Ascension (J2000)
23- 24 I2 min RAm Minute of Right Ascension (J2000)
26- 29 F4.1 s RAs Second of Right Ascension (J2000)
31 A1 --- DE- Sign of the Declination (J2000)
32- 33 I2 deg DEd Degree of Declination (J2000)
35- 36 I2 arcmin DEm Arcminute of Declination (J2000)
38- 39 I2 arcsec DEs Arcsecond of Declination (J2000)
41- 43 F3.1 kpc Dist Distance
45 A1 --- l_F24 Limit flag on F24
46- 50 F5.2 Jy F24 Spitzer/MIPS 24 micron band flux density
52- 57 F6.2 Jy F55 ? Spitzer 55um flux density
59- 64 F6.2 Jy F65 ? Spitzer 65um flux density
66- 71 F6.2 Jy F75 ? Spitzer 75um flux density
73- 78 F6.2 Jy F85 ? Spitzer 85um flux density
80- 85 F6.2 Jy F95 ? Spitzer 95um flux density
87- 92 F6.2 Jy F350 ? CSO 350um flux density
94- 98 F5.2 Jy F450 ? CSO or JCMT 450um flux density
100-104 F5.2 Jy F850 ? JCMT 850um flux density
106-109 F4.2 Jy F1200 IRAM 1.2mm flux density
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- MSXDC The IRDC core identification (GLLL.ll+DD.dd MMNN)
20- 21 I2 K Tdust Dust temperature
23- 27 F5.3 --- tau250 Optical depth at 250 microns
29- 31 F3.1 --- beta Dust emissivity index
33- 37 I5 Lsun Lum Luminosity
39- 42 I4 Msun Mass Mass
44- 48 F5.2 [cm-2] logNH2 Log of the beam-average H2 column density
50- 53 F4.2 [cm-3] lognH2 Log of the volume-average H2 density
55 A1 --- l_chi2 Limit flag on chi2
56- 60 F5.2 --- chi2 The χ2 of best fit
62 A1 --- Cl [ABIQR] Classification (G1)
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- MSXDC The IRDC core identification (GLLL.ll+DD.dd MMNN)
20- 21 I2 K b_Tdust Lower limit of dust temperature
23- 24 I2 K B_Tdust Upper limit of dust temperature
26- 30 F5.3 --- b_tau250 Lower limit of optical depth at 250 microns
32- 36 F5.3 --- B_tau250 Upper limit of optical depth at 250 microns
38- 40 F3.1 --- b_beta Lower limit of dust emissivity index
42- 44 F3.1 --- B_beta Upper limit of dust emissivity index
46- 48 I3 Lsun b_Lum Lower limit of luminosity
50- 53 I4 Lsun B_Lum Upper limit of luminosity
55- 58 I4 Msun b_Mass Lower limit of mass
60- 62 I3 Msun B_Mass Upper limit of mass
64 A1 --- lbchi2 Limit flag on b_chi2
65- 69 F5.2 --- b_chi2 Lower limit of χ2 of best fit
71 A1 --- lBchi2 Limit flag on B_chi2
72- 76 F5.2 --- B_chi2 Upper limit of χ2 of best fit
78 A1 --- Cl [BIQR] Source classification (G1)
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Global notes:
Note (G1): Based on the IRAC colors and the presence or absence of 24
micron emission. See section 4.1 for further details.
The classification code is:
B = blue
I = intermediate
R = red
A = active
Q = quiescent
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Nomenclature notes:
The cores are <[RJS2006] MSXDC GLLL.ll+DD.dd MMNN> in Simbad
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 27-Apr-2012