J/ApJ/428/693 Rosette Nebula and Maddalena Cloud structures (Williams+ 1994)
Determining structure in molecular clouds.
Williams J.P., De Geus E.J., Blitz L.
<Astrophys. J. 428, 693 (1994)>
=1994ApJ...428..693W 1994ApJ...428..693W (SIMBAD/NED BibCode)
ADC_Keywords: Nebulae ; Morphology
Keywords: ISM: clouds - ISM: individual (Rosette Nebula, Maddalena Cloud) -
ISM: structure - methods: analytical - stars: formation
Abstract:
We describe an automatic, objective routine for analyzing the clumpy
structure in a spectral line position-position-velocity data cube.
The algorithm works by first contouring the data at a multiple of the
rms noise of the observations, then searches for peaks of emission
which locate the clumps, and then follows them down to lower
intensities. No a priori clump profile is assumed. By creating
simulated data, we test the performance of the algorithm and show that
a contour map most accurately depicts internal structure at a
contouring interval equal to twice the rms noise of the map. Blending
of clump emission leads to small errors in mass and size
determinations and in severe cases can result in a number of clumps
being misidentified as a single unit, flattening the measured clump
mass spectrum. The algorithm is applied to two real data sets as an
example of its use. The Rosette molecular cloud is a "typical"
star-forming cloud, but in the Maddalena molecular cloud high-mass
star formation is completely absent. Comparison of the two clump lists
generated by the algorithm show that on a one-to-one basis the clumps
in the star-forming cloud have higher peak temperatures, higher
average densities, and are more gravitationally bound than in the non
star-forming cloud. Collective properties of the clumps, such as
temperature-size-line-width-mass relations appear very similar,
however. Contrary to the initial results reported in a previous paper
(Williams & Blitz, 1993ApJ...405L..75W 1993ApJ...405L..75W), we find that the current,
more thoroughly tested analysis finds no significant difference in the
clump mass spectrum of the two clouds.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 46 88 Clumps in the Rosette molecular cloud
table3a.dat 39 53 Clumps in the Maddalena molecular cloud:
region 1 (RA=6h46m50s, DE=-4°31'14")
table3b.dat 39 39 Clumps in the Maddalena molecular cloud:
region 2 (RA=6h43m39s, DE=-3°30'23")
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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- 2 I2 --- RMC [1/95]+ Clump number ([WDB94] RMC NN in Simbad)
4- 10 F7.3 deg GLON Peak galactic longitude
12- 17 F6.3 deg GLAT Peak galactic latitude
19- 22 F4.1 km/s Vpeak Peak velocity
24- 26 F3.1 K Tpeak Peak temperature
28- 31 F4.2 pc DR Equivalent circular radius (1)
33- 36 F4.2 km/s FWHM Line width (1)
38- 41 I4 solMass Mlte Clump masses (2)
43- 46 I4 solMass Mvir Virial mass (3)
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Note (1): Data corrected for beam size as described in Appendix A
Note (2): Clump masses, derived from the integrated 13CO luminosity assuming
LTE, τ13<0.5, NH2/N13CO=4.8x105, and Tex=20K.
Includes an additional factor of 1.4 for helium.
Note (3): Virial mass, assuming an inverse-square power-law density profile
(see Appendix A)
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Byte-by-byte Description of file: table3a.dat table3b.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- MMC [1/58]+ Clump number (1)
4- 6 I3 arcmin oRApeak Offset from right ascension (2)
8- 10 I3 arcmin oDEpeak Offset from declination (2)
12- 15 F4.1 km/s Vpeak Peak velocity
17- 19 F3.1 K Tpeak Peak temperature
21- 24 F4.2 pc DR Equivalent circular radius (3)
26- 29 F4.2 km/s FWHM Line width (3)
31- 34 I4 solMass Mlte Clump masses (4)
36- 39 I4 solMass Mvir Virial mass (5)
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Note (1): table3a.dat: [WDB94] MMC-1 NN in Simbad
table3b.dat: [WDB94] MMC-2 NN in Simbad
Note (2): For table3a.dat, RA=6h46m50s, DE=-4°31'14"
For table3b.dat, RA=6h43m39s, DE=-3°30'23"
Note (3): Data corrected for beam size as described in Appendix A
Note (4): Clump masses, derived from the integrated 13CO luminosity assuming
LTE, τ13<0.5, NH2/N13CO=4.8x105, and Tex=10K.
Includes an additional factor of 1.4 for helium.
Note (5): Virial mass, assuming an inverse-square power-law density profile
(see Appendix A)
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History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 12-Oct-1998