A Catalog of Molecular Gas at High Galactic Latitudes

Abstract

The global distribution and physical properties of the high-latitude molecular clouds are tabulated and discussed. As of this writing, more than 100 objects have been identified at Galactic latitudes |b| > 25°. Positions are listed for all the known clouds and LSR velocity, angular extent, mass, and internal velocity dispersion are listed when such data are available from the literature. The high-latitude molecular clouds consist primarily of translucent clouds, so that this catalog is the largest, most complete compendium of these objects at high Galactic latitudes. The velocity dispersion of the ensemble of clouds is 5.8 km s-1 if seven intermediate velocity objects are excluded and 9.9 km s-1 otherwise. The former dispersion implies a scale height for the clouds of 124 pc and a mean distance of 150 pc; the latter dispersion yields 210 pc and 260 pc, respectively. Thus, the majority of high-latitude clouds are local objects that may be situated at the nearer edges of the Local Bubble. As a group, they are the nearest molecular clouds to the Sun. The average velocity of the ensemble of clouds is -0.3 km s-1 without the intermediate velocity objects and -2.4 km s-1 including these clouds. From the catalog of clouds, we determine values for the filling fraction and mass surface density of the high-latitude molecular clouds (and thus of translucent gas) of 0.005 and 0.1-0.2 M0 pc -2, respectively, at |b| > 25°. Including the lower latitude contribution, we estimate the total local mass surface density of translucent clouds to be 0.2-0.3 M_sun pc-2 In the local interstellar medium, these objects represent from 10% to 20% of the molecular gas inventory. Individual clouds range in size from less than 10-1 to 101 pc and in mass from 10-1 to 103 M_sun. An asymmetry between the northern and southern Galactic hemisphere distribution of the clouds can be interpreted as a displacement of the Sun from the Galactic midplane of 18 pc, a value consistent with determinations based on other tracers.

A Catalog of Molecular Gas at High Galactic Latitudes

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