HI Shells and Supershells in the I-GALFA HI 21-cm Line Survey

We search for fast-expanding Hi shells associated with Galactic supernova remnants (SNRs) in the longitude range l ≈ 32 to 77 using 21-cm line data from the Inner-Galaxy Arecibo L-band Feed Array (I-GALFA)Hi survey. Among the 39 known Galactic SNRs in this region, we find such Hi shells in four SNRs: W44, G54.4−0.3, W51C, and CTB 80. All four were previously identified in lowresolution surveys, and three of those (excluding G54.4 − 0.3) were previously studied with the Arecibo telescope. A remarkable new result, however, is the detection ofHi emission at both very high positive and negative velocities in W44 Department of Physics and Astronomy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea Department of Physics and Astronomy, Western Kentucky University, Bowling Green, KY 42101, USA Arecibo Observatory, HC 3 Box 53995, Arecibo, PR 00612, USA Yonsei University Observatory, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, Republic of Korea Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 305-348, Republic of Korea Department of Electrical and Computer Engineering, San Diego State University, San Diego, CA 92182, USA University of Calgary/Dominion Radio Astrophysical Observatory, P.O. Box 248, Penticton, BC V2A 6J9, Canada Department of Astronomy, Columbia University, New York, NY 10027, USA Hubble Fellow Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA Radio Astronomy Lab, UC Berkeley, 601 Campbell Hall, Berkeley, CA 94720, USA Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada Corresponding author; koo@astro.snu.ac.kr