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High-sensitivity 21-cm maps made with the Hat Creek 85-foot telescope towards the Galactic anticenter reveal a wealth of filamentary structure at intermediate negative velocities. No corresponding structure is seen at positive velocities. In order to study this filamentary structure a median filtering technique is used to remove the smooth, slowly-varying background. Structures with widths less than about $5\deg$ are preserved.
The filaments are oriented primarily parallel to the Galactic plane. They cover a range of lengths between $5\deg$ and $20\deg$. Their curvatures are similar to those of lines of constant longitude seen on the surface of a tilted sphere centered near $l=180\deg$ and $b=0\deg$ with a radius of about $25\deg$. They are easily visible at intermediate velocities but become tangled in a web of filamentary structures at $V_{\rm LSR} > -17$ km s$^{-1}$.
In this work, I present models of filaments on the surface of such a sphere. The models are constrained to match the observations in both projected position and radial velocity relative to the local standard of rest. The most interesting and more difficult fit is to the velocity information. Velocity fields resulting from systemic motion, spherical expansion, differential rotation, and tangential motion along the surface of the sphere are among those considered.
This research has been supported in part by NSF grant FD91-23362 to Carl Heiles.
