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By comparing radial velocities of radio bright compact HII regions with theirHI absorption profiles, we discovered expanding shells of neutral hydrogenaround them. These shells are revealed by absorption of the radio continuumemission from the HII regions at velocities indicating greater distances thanthe observed radial velocity. We believe that these shells are shock zones atthe outer edge of the expanding ionized region. Additionally we found evidencefor a velocity inversion inside the Perseus arm caused by a spiral shock, whichresults in a deep absorption line in the spectra of compact HII regions behindit.Comment: 8 pages, 11 figures. accepted for publication in Astronomy and  Astrophysic

Expanding shells of shocked neutral hydrogen around compact HII regions