Carbon Monoxide Observations of Small Dark Globules. I. Internal Structure

Abstract

To probe internal structures of small interstellar clouds, we have observed 12 dark globules in the emission of CO isotopes. Full mappings were made in the transition of 13CO(J = 1 → 0), while in the 12CO only cross-scan observations were done. We have identified 18 subcondensations from the column-density maps of the 12 globules and derived various physical properties for each of them. The line widths of most subcondensations show little variation with distance from center. Some of the condensations, however, seem to undergo systematic motions of expansion or contraction. The internal density structure of the subcondensations closely resembles that of the truncated isothermal gas sphere. The observed line width ΔV of the subcondensations varies with the size, R, in a power-law fashion, ΔV ∝ Rβ, with β = 0.61 ± 0.11, which is a somewhat steeper exponent than the one for the cores of giant molecular clouds. The result is compared with those from a wide variety of interstellar clouds.