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K. Wood, M. Spaans (SAO), A. Witt (Toledo), K. Gordon (LSU)
We have constructed model H I column density maps starting from an initial smooth prescription of the H I that we made clumpy with a random algorithm. As we increase the volume filling factor of overdense cubes in our three dimensional H I grid we see the apparent formation of worm-like structures that peak around the percolation threshold (ffPT=25%) of a three dimensional lattice. For lower and higher filling factors the column density maps appear respectively bubblier and smoother than real observations. The filling factor we derive is in agreement with that found from more detailed analyses of H I data and simulations. Applying a median filtering to our simulations we find many worm-like candidates reminiscent of those found in H I, IRAS, and radio continuum data. We have further constructed maps of the column density in concentric shells of width 200pc and find that structures persist in these images also. We also find evidence that structures can arise that give the appearence of expanding shells. Based on our physics free model, we suggest that many of the worm-candidates that are not associated with H II regions or progenitor OB associations may just be random structure formation at the precolation threshold of a three dimensional lattice.
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