Star Formation at High Galactic Latitude:
A Case for Extensions to the Survey

High-Latitude Clouds

Until recently, most studies of star formation have been confined to large molecular clouds near the Galactic plane, such as Taurus and Orion. However, both greater sensitivity of the receivers detecting radio emission lines as well as the all-sky surveys of IRAS and later satellites have made possible the discovery and study of more tenuous molecular material. Although these clouds are thought to exist throughout the Galaxy, they are most easily observed at high latitude above the molecular scale height where sightlines are particularly simple. Over a hundred high-latitude molecular clouds (HLCs) have been found in regions obscured on photographic plates and in regions of 100 excess emission due to dust associated with molecular gas. HLCs exhibit a wide range of morphologies and sizes, from small dense clumps to filaments several degrees long, and spatial structure down to the smallest observable scales. In general, HLCs are translucent (), located within a few hundred parsecs of the Sun, quiescent and not gravitationally bound (review in Magnani et al. 1996).

In an effort to constrain models of the evolution of dust in the interstellar medium, we are currently observing interstellar extinction and polarization curves toward HLCs. Preliminary results suggest that, in general, the dust in HLCs has optical properties not unlike dust observed in the Galactic plane. However, we have found large variation in the environmentally-sensitive relationship between polarization and extinction within and among HLCs. We are currently investigating how the polarization efficiency (p/A) and the ratio of total-to-selective extinction () in HLCs is correlated to the presence of TTauri stars at high-latitude.

© Copyright Astronomical Society of Australia 1997