ar X iv : a st ro - p h / 01 07 18 4 v 1 1 0 Ju l 2 00 1 Properties of a Molecular Cloud in NGC 185
نویسنده
چکیده
The dwarf elliptical galaxy NGC 185— the closest early-type galaxy with detectable molecular gas— offers a unique opportunity for high angular resolution studies of the interstellar medium in early-type galaxies. I present interferometric images (17 pc × 14 pc resolution) of CO emission from NGC 185. The majority of the molecular gas in NGC 185 is in one resolved cloud, closely associated with dust and an HI structure which may be a photodissociated envelope. The high spatial resolution also reveals a velocity gradient across the cloud, which allows a dynamical mass estimate independent of the H 2 /CO conversion factor or the virial theorem. The linear sizes, velocity gradients, and dynamical masses of the molecular clouds in NGC 185 and NGC 205, a similar dwarf elliptical, are comparable to those of the largest Galactic giant molecular clouds (GMCs). If the dynamical masses of the clouds are assumed to be good estimates of their true masses, the inferred H 2 /CO conversion factor in NGC 185 is at least eight times larger than a standard Galactic conversion factor, and the reasons for this difference are not yet understood. In any case, it seems clear that structures similar to Galactic GMCs can form in small elliptical or early type galaxies, even in the absence of spiral density waves.
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