The Clump Spectrum of Two High-Latitude Molecular Clouds

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Session 30 -- Star Formation, Molecular Clouds and HII Regions
Display presentation, Tuesday, 31, 1994, 9:20-6:30

[30.04] The Clump Spectrum of Two High-Latitude Molecular Clouds

Leo Blitz, Marc W. Pound (UMD)

We have applied the clump-finding program of Williams et. al. (1994) to two high galactic latitude molecular clouds. The data consist of large-scale, well-sampled $^{13}$CO(1-0) and CO(1-0) maps of the high-latitude clouds MBM12 (=L1457) and MBM41-44 (Draco Nebula), and have about 500,000 pixels each. This is the first application of the clump-finder to HLCs as well as to large datasets. In each cloud, we find more than 200 clumps ranging from a few hundredths of a solar mass to a few solar masses. We derive the total mass of MBM12 to be 150 ${\rm M_{\sun}}$ and of MBM41-44 to be 140 ${\rm M_{\sun}}$. In both clouds, the high sensitivity of the maps allow determination of the mass spectrum including substellar mass clumps ($M < 0.08~{\rm M_{\sun}}$). We find that the clump mass spectrum in MBM41-44 has power-law index $\alpha=1.40~\pm~0.06$, similar to that found for giant molecular clouds. MBM12, however, has a shallower spectrum, $\alpha =1.07~\pm~0.05$. (The quoted errors are statistical uncertainties.) It is surprising that the clump mass spectrum for MBM41-41, a cloud complex far from being gravitationally bound, has the same mass spectrum as the Rosette complex, a well-studied giant molecular cloud.

We compare the derived HLC quantities to the results of Williams etal for the Rosette molecular cloud. We find that the HLCS have a significantly steeper size-linewidth relation than the Rosette ($\Delta V \sim R^{0.7}$ for HLCs; $\Delta V \sim R^{0.4}$ for the Rosette). We describe a method to determine the internal clump density profile for pressure-bound clumps from the size-linewidth relation. In principle, this method will work even for unresolved clumps. Finally, we report the discovery of a new cloud in the Draco Nebula ``chain.''

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