Properties of the molecular clouds in NGC 205

摘要

The nearby dwarf elliptical galaxy NGC 205 offers a unique opportunity for high-resolution studies of the interstellar medium in an elliptical galaxy. The present paper investigates the distribution of molecular gas, molecular line ratios, and the relationships between atomic gas, molecular gas, and dust in this galaxy. The line ratios (CO)-C-12 (2-1)/(1-0) and (CO)-C-12 (1-0)/(CO)-C-13 (1-0) in one of the molecular clouds in NGC 205 are consistent with the ratios found in other elliptical galaxies and in Galactic giant molecular clouds; they suggest that the CO in this cloud is probably subthermally excited. Atomic gas, molecular gas, and dust are very closely associated on scales of similar to 100 pc; the atomic gas can be understood as a photodissociated envelope around the molecular clouds. The atomic column densities in this galaxy are quite low (approximate to 10(20) cm(-2)) because the interstellar UV field is relatively low. The total gas-to-dust column density ratios are consistent with Galactic gas-to-dust ratios. In short, the molecular gas in NGC 205 seems to have properties very similar to the familiar molecular clouds in our own Galaxy except for the low atomic column densities. References: 61