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J/ApJ/428/693 Rosette Nebula and Maddalena Cloud structures (Williams+ 1994)
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Beginning of ReadMe :J/ApJ/428/693 Rosette Nebula and Maddalena Cloud structures (Williams+ 1994)
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Determining structure in molecular clouds.
Williams J.P., De Geus E.J., Blitz L.
<Astrophys. J. 428, 693 (1994)>
=1994ApJ...428..693W (SIMBAD/NED BibCode)
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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), we find that the current,
more thoroughly tested analysis finds no significant difference in the
clump mass spectrum of the two clouds.