A Search for Narrow Vertical Structures in the Canadian Galactic Plane Survey

Worms are defined to be dusty, atomic hydrogen (HI) structures which areobserved in low resolution data to rise perpendicular to the Galactic plane.Data from the 1'-resolution Canadian Galactic Plane Survey (CGPS) weresystematically searched for narrow vertical HI structures which could beresolved worms. Another motivation for the search was to explore the scenariothat mushroom-shaped worms like GW123.4-1.5, studied by English andcollaborators, could be generated by a single supernova. However no othervertical structures of mushroom-shape morphology were found. We also examinedobjects previously classified as worm candidates by Koo and collaborators; only7 have a significant portion of their structure falling in the CGPS range ofl=74 deg to 147 deg, -3.5 deg < b < +5.5 deg. Apart from GW123.4-1.5 we couldnot confirm that any of these are coherent structures that extend towards theMilky Way's halo. However a list of 10 narrow, vertical structures found in oursearch is furnished; one structure is >~ 500 pc tall, thus extending from theGalactic plane into the halo. We provide details about these narrow verticalstructures, including comparisons between HI, radio continuum, IR, and COobservations. Our search was conducted by visual inspection and we describe thelimitations of this approach since it indicates that only 6 disk-halo featuresmay exist throughout the Milky Way. We also discuss possible origins ofstructures at high latitudes and the relationship between mushroom-shapedclouds and old supernova remnants.