2025ApJ...980..267J

We present case studies comparing the global H I and Hα emission line profiles of six galaxy pairs. The six pairs are selected to have different nuclear activities, with two hosting an active galactic nucleus, and in different merging stages-two of each from the premerging, merging, and postmerging stages. We observe their global H I spectra with the Five-hundred-meter Aperture Spherical radio Telescope, achieving a noise level of ∼0.5 mJy. Five out of the six pair systems have secure detections of H I emissions (signal-to-noise ratio > 10). The H I fraction and star formation efficiency of the six pairs do not deviate from isolated galaxies. For the H I line profiles, common unique asymmetry is observed, indicating disturbances of the atomic gas from the galaxy interaction. The global Hα spectra of the merger systems are constructed from the optical integral field spectroscopic observations by integrating the flux in corresponding line-of-sight velocity bins. The Hα spectra tend to show multiple components in the premerger phase and single-component line profiles in the postmerger systems, while all H I spectra show single-component line profiles regardless of merger stages. The H I and Hα spectra show offsets in the central velocities, which appear to decrease from >100 km s^–1 in the premerger pair to <10 km s^–1 in the postmergers. This trend is consistent with the scenario that, despite the significantly different distributions and kinematics of the atomic and ionized gases, the merging process may contribute to the mixing and eventually align various gas contents.