The High-Latitude Cloud MBM 7. I. H i and CO Observations

Details The High-Latitude Cloud MBM 7. I. H i and CO Observations The High-Latitude Cloud MBM 7. I. H i and CO Observations

Aug 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...467..717m&link_type=abstract

Astrophysical Journal v.467, p.717

Astronomy and Astrophysics

Astronomy

10

Shock Waves, Ism: Clouds, Ism: Molecules, Ism: Individual Alphanumeric: Mbm 7, Radio Lines: Ism

Scientific paper

The high-latitude cloud (HLC) MBM 7 has been observed in the 21 cm H I line and the 12C0(1-0) and 13Co(1-0) lines with similar spatial resolutions. The data reveal a total mass ˜30 Msun for MBM 7 and a complex morphology. The cloud consists of a cold dense core of 5 Msun surrounded by atomic and molecular gas with about 25 Msun, which is embedded in hotter and more diffuse H I gas. We derive a total column density N(H I + 2H2) of 1 x 1021 cm-2 toward the center and 1 x 1020 cm-3 toward the envelope of MBM 7. The CO line indicates the existence of dense cores [n(H2) ≥ 2000 cm-3] of size (FWHM) ˜0.5 pc.
The morphology suggests shock compression from the southwest direction, which can form molecular cores along the direction perpendicular to the H I distribution. The H I cloud extends to the northeast, and the velocity gradient appears to be about 2.8 km s-1 pc-1 in this direction, which indicates a systematic outward motion which will disrupt the cloud in ˜106 yr. The observed large line widths of ˜2 km s-1 for CO suggest that turbulent motions exist in the cloud, and hydrodynamical turbulence may dominate the line broadening. Considering the energy and pressure of MBM 7, the dense cores appear not to be bound by gravity, and the whole cloud including the dense cores seem to be expanding.
The distance to HLCs suggest that they belong to the galactic plane, since the scale height of the cloud is ≤100 pc. Compared to the more familiar dense dark clouds, HLCs may differ only in their small mass and low density, with their proximity reducing the filling factor and enhancing the contrast of the core and envelope structure.

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