J/ApJ/644/990 Sub-mm clumps at 450 and 850µm in M17 (Reid+, 2006)
High-mass star formation. II. The mass function of submillimeter clumps in M17.
Reid M.A., Wilson C.D.
<Astrophys. J., 644, 990-1005 (2006)>
=2006ApJ...644..990R 2006ApJ...644..990R
ADC_Keywords: Interstellar medium ; Millimetric/submm sources
Keywords: ISM: individual (M17) - ISM: structure - methods: data analysis -
stars: formation - submillimeter
Abstract:
We have mapped a 5.5x5.5pc portion of the M17 massive star-forming
region in both 850 and 450µm dust continuum emission using the
Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk
Maxwell Telescope (JCMT). The maps reveal more than 100 dusty clumps
with deconvolved linear sizes of ∼0.05-0.2pc and masses of
∼0.8-120M☉, most of which are not associated with known
mid-infrared point sources. Fitting the clump mass function with a
double power law gives a mean power-law exponent of
αhigh=-2.4±0.3 for the high-mass power law, consistent with
the exponent of the Salpeter stellar mass function. We show that a
lognormal clump mass distribution with a peak at 4M☉ produces as
good a fit to the clump mass function as does a double power law. This
4M☉ peak mass is well above the peak masses of both the stellar
initial mass function and the mass function of clumps in low-mass
star-forming regions. Despite the difference in intrinsic mass scale,
the shape of the M17 clump mass function appears to be consistent with
the shape of the core mass function in low-mass star-forming regions.
Thus, we suggest that the clump mass function in high-mass
star-forming regions may be a scaled up version of that in low-mass
regions, instead of its extension to higher masses.
Description:
We used the Submillimeter Common-User Bolometer Array on the James
Clerk Maxwell Telescope (JCMT) to map an approximately 12'x12'
(5.5x5.5pc) region of M17. The data were acquired on the nights of
2003 March 17 and April 16 with a total on-source integration time of
about 5hr.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 95 121 Properties of the 850um Clumps
table2.dat 95 101 Properties of the 450um Clumps
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See also:
J/ApJ/625/891 : Sub-mm clumps at 450 and 850µm in NGC 7538 (Reid+, 2005)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- [RW2006b] Name SNN NNN (1)
8 A1 --- m_[RW2006b] [ABC] Multiplicity index for clump (1)
9 A1 --- n_[RW2006b] [e] Note on Name (2)
11- 12 I2 h RAh Right ascension (J2000)
14- 15 I2 min RAm Right ascension (J2000)
17- 20 F4.1 s RAs Right ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 30 I2 arcsec DEs Declination (J2000)
32- 35 F4.2 pc Reff Effective radius
37- 41 F5.2 Jy Speak Peak flux density at 850um for table1 and
450um for table2, in Jy/beam
43- 46 F4.2 Jy e_Speak rms uncertainty on Speak (3)
48- 52 F5.2 Jy Sint Integrated flux density at 850um for table1
and 450um for table2
54- 58 F5.2 Jy e_Sint rms uncertainty on Sint (3)
60- 63 F4.2 --- alpha ?=- Spectral index
(only in table1) (4)
65- 67 I3 K Td ?=- Dust temperature (only in table1) (5)
69- 74 F6.2 solMass M(30K) ?=- Mass calculated with fixed Td (Td=30K)
76- 80 F5.2 solMass e_M(30K) ? rms uncertainty on M(30K) (3)
82- 87 F6.2 solMass M(Td) ?=- Mass calculated with estimated Td
(only in table1)
89- 93 F5.2 solMass e_M(Td) ? rms uncertainty on M(Td) (3)
(only in table1)
95 I1 --- Npsc Number of MSX point sources contained
within the clump's 0.5Speak contour
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Note (1): Names in Simbad are [RW2006b] SMM NNN in table1 and
[RW2006b] SMM NNNA in table2.
The names of the 450um clumps have been set to reflect the names of
the 850um clumps in which their peaks appear. Thus, clumps SMM 21A-21C
are the three 450um clumps whose peaks appear within the
boundaries of 850um clump SMM 21.
Note (2): "e" denotes a clump to which corrections for free-free emission
have been applied in the calculation of the spectral index, dust
temperature, and masses. The free-free correction has not been applied
to the peak and integrated fluxes listed here.
Note (3): The uncertainties stated in this table are composed of the
uncertainties in the gain calibration, the sky opacities, and the
corrections due to the error beam. These uncertainties are typically
significantly larger than the random measurement errors associated
with the rms flux of the map. The exception is the peak flux, where
the random error of sigma=0.027Jy/beam (table1) or sigma=0.32Jy/beam
(table2) dominates the systematic error for the clumps with lower peak
fluxes.
Note (4): The systematic uncertainty in the spectral index, alpha, is 13%.
These systematic uncertainties, which are composed of the
uncertainties in the gain calibration and sky opacities, dominate the
random errors on the spectral index.
Note (5): See Sect. 3.2 for a discussion of the uncertainties in the
temperatures. Temperatures are omitted where high spectral index makes
them incalculable or where no reliable spectral index can be
calculated (see text). All of the temperatures above 40K should be
considered highly uncertain, indicating only that a clump is probably
hot.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 02-Oct-2007