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Clump mass spectra of molecular clouds

Carsten Kramer, Jürgen Stutzki, Ralf Röhrig, and Uwe Corneliussen
Universität zu Köln, I. Physikalisches Institut, Zülpicher Strasse 77, D-50937 Köln, Germany
Abstract: We present clump mass spectra of the seven molecular clouds L1457, MCLD 126.6+24.5, NGC 1499SW, Orion B South, S140, M17SW, and NGC 7538, which were derived by a Gaussian clump decomposition algorithm from large scale isotopomeric CO maps.

We discuss in detail the reliability of the mass spectra derived by studying their dependence on the control parameters of the decomposition algorithm.

All clump mass spectra found are consistent with a power law, tex2html_wrap_inline613 , with tex2html_wrap_inline615 between 1.6 and 1.8. Due to the different resolution of the observations and the different distances of the clouds, the clump masses range from several tex2html_wrap_inline747 M tex2html_wrap_inline749 in NGC 7538 down to tex2html_wrap_inline751 M tex2html_wrap_inline749 , less than the mass of Jupiter, in the nearby cloud L1457. The large dynamic range covered by the observations is reflected by the high number of clumps found in each cloud, which lie between 100 and 1300. The spectral index of the clump mass distributions thus is independent of the wide range of physical properties of the clouds studied. In particular, there are no indications of a turnover of the clump mass power law index at a characteristic clump mass such as the Jeans mass, below which the clumps become gravitationally unbound. This is particularly emphasized by the clump properties in L1457 most of which are clearly sub stellar and which are far from being gravitationally bound objects (Fig 4).

Figure 4: Clump mass spectra of the eight data sets analyzed. All spectra are fitted by a power law function tex2html_wrap_inline613 . The straight lines represent the best linear fit over the range of masses spanned by the line. The resulting indices tex2html_wrap_inline615 lie in the range 1.59 to 1.79. .

Accepted by Astronomy & Astrophysics
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