HI Observations of Dust Clouds

Citation

Chu, Kwong Wah (1975) HI Observations of Dust Clouds. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/FFYW-J027. https://resolver.caltech.edu/CaltechETD:etd-09092008-081132

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Aperture synthesis observations of three dust clouds, L134, L1495 and L1517, were made at 21 cm. A 7 arc min diameter beam was synthesized, and the velocity resolution was 0.2 km/sec. In addition to interferometer observations, single dish measurements were carried out to provide large scale information. Two dust clouds, L134 and L1495, were detected in absorption against background 21 cm emission. In both cases the 21 cm absorption line is at a velocity coincident with molecular lines detected in the dust clouds. The hydrogen responsible for the absorption line has a spin temperature less than 2[...] K, and the columnar atomic hydrogen density through the dust clouds is between [...] and [...]. Based upon optical extinction and normal cosmic abundances, the expected hydrogen content is [...]. It is presumed that most of the hydrogen is in molecular form. L134 consists of two velocity components separated by 2 km/sec. Fragmentation of a larger cloud into two smaller components may explain the data, but more evidence is needed to draw any firm conclusion. Within an individual velocity component, no significant substructure was detected in L134 or L1495. The optical appearance of L1517 strongly suggests a fragmented structure, but this dust cloud was not detectable at 21 cm. L1517 may be sufficiently dense that the amount of residual atomic hydrogen is too small to detect, but this conjecture remains to be substantiated.

Thesis Files