Neutral hydrogen detectability given unknown systemic velocities

Ascertain whether any neutral hydrogen 21-cm line emission from Sculptor A, Sculptor B, and Sculptor C is concealed within Milky Way emission due to unknown systemic velocities, in order to validate the inferred upper limits on their neutral gas content from the Galactic All Sky Survey.

Background

The authors report non-detections of H I in HIPASS and derive 3σ upper limits on H I masses using GASS cubes over −500 < v/km s−1 < 500. They explicitly caution that, without prior velocity measurements for the dwarfs, their H I lines could overlap with Milky Way emission, potentially masking a detection.

They also note that their upper limits would not apply if any dwarf’s velocity lies outside the searched range, emphasizing the need for systemic velocity measurements and deeper targeted H I observations to confirm whether these systems are truly gas-free.