5 Conclusions

We have mapped (parts of) the HLC MBM 32 in ¹²CO(1-0), (2-1), and (3-2), and in ¹³CO(1-0) and (2-1). A summary of our results is given in Table 7.

Our ¹²CO(1-0) map of MBM 32 shows that the cloud consists of three components, which can be distinguished by their radial velocity. The main (eastern) component, at $V_{\rm {lsr}}>2$ km$\,$s^-1 has a mass (derived from ¹²CO(1-0) data) of about 16.9 $M_\odot$. The (western) component at $V_{\rm {lsr}}<0$ km$\,$s^-1 has 4.1 $M_\odot$, and the emission in the range in between both velocities has 0.46 $M_\odot$.

The CO spectra are fairly simple and contain no signs of self-absorption or strong, broad line wings. At most positions only one velocity component is detected, except for the main component which is overlapping with the eastern component. Within the main component there is possibly some overlap between emission at 2.0 km$\,$s^-1 and at 3.5 km$\,$s^-1. Strong H I emission is found from 100-m Effelsberg measurements towards the eastern component, but spectra show that there is H I emission associated with all three molecular components. The mass of H I gas is about equal to that of the H₂. For some of the emission we see velocity differences between CO and H I emission between -1.5 and +1.5 km$\,$s^-1.

Correcting the FIR (60 and 100 $\mu$m) emission for contribution of dust associated with the H I there is a good correlation between dust and CO emission. The X ratio N(H $_2)/\int T_{\rm {R}}^*(^{12}$CO(1-0))dv derived from the combination of CO, FIR, and H I data ( $0.2\ 10^{20}$) is lower than that derived assuming LTE from the CO data alone ( $0.7\ 10^{20}$). Part of the differences might be due to the adopted ¹³CO abundance, which is uncertain in HLCs.

From the ratio of 60 and 100 $\mu$m emission we derive a constant dust temperature of 20 K. The ratio of gas to dust mass, 236, is lower than derived from FIR-CO comparisons in other clouds. This suggests that there is relatively less cold dust.

Apart from the ratio ¹²CO( 1-0)/¹³CO(1-0), line ratios of different CO transitions appear to be constant within different cloud components. In particular this is found from deep measurements along a cut through the cloud in ¹²CO(2-1) and (3-2), and in ¹³CO(2-1). The ratio ¹²CO/¹³CO of $T_{\rm {R}}^*$ and of $\int T_{\rm {R}}R^*$dvis higher than typical ratios in galactic giant molecular clouds, indicating the lower optical depth of CO. The constant line ratios may suggest a cloud model consisting of small (<<beam size) clumps, with approximately the constant size and density distribution within the cloud, where the line intensities are determined by the clump filling factors.

The emission was subdivided in Gaussian clumps. For the main components typically 40-50% of the mass is found to be in clumps with $T_{\rm {R}}^*$ above a 3 rms level. The size of the clumps is between about 0.4 pc and the resolution limit of $\approx$0.07 pc. From the ¹²CO(1-0) and (2-1) data we obtain for these clumps a correlation $\delta v\propto r^{0.45}$, close to values found for other cloud samples.

Acknowledgements

We thank all KOSMA-observers who observed MBM 32 when their own sources were below the horizon. Comments on an earlier version of this paper by J. Brand and C. Kramer are appreciated. The KOSMA radio telescope at Gornergrat-Süd observatory is operated by the University of Köln, and supported by the Deutsche Forschungsgemeinschaft through grant SFB-301, as well as by special funding from the Land Nordrhein-Westfalen. The observatory is administered by the Internationale Stiftung Hochalpine Forschungsstationen Jungfraujoch und Gornergrat, Bern, Switzerland.