2015AJ....149..189S

Galactic H i (neutral hydrogen) shells are central to our understanding of the interstellar medium, which plays a key role in the development and evolution of galaxies, including our own. Several models involving supernovae (SNe) and stellar winds have contributed to our broad understanding, but a complete, detailed picture remains elusive. To extend existing Galactic shell catalogs, we visually examined the SETHi (Search for Extraterrestrial H i) database to identify shell-like structures. This high-sensitivity 21 cm radio survey covering the Arecibo sky uniquely provides high-resolution data on shells at a wide range of Galactic latitudes. We present basic information (location, radial velocity, angular size, shape) for 74 previously unidentified H i shells. Due to limitations of coverage and data quality, and the biases inherent in search techniques, our catalog is not a complete sample of Galactic shells. We discuss the catalog completeness, and comment on the new shells' relationship with known interstellar structure as warranted. Unlike many previous catalogs, this sample is not biased toward expanding shells. Where possible we also estimate the kinematic distances, physical sizes, expansion velocities, and energies of these shells. Overall, they are relatively large and old, each the result of multiple SNe. Unlike previous surveys, we do not find that the shells in our sample are preferentially aligned relative to the Galactic plane.