Comparison of Global HI and H$\alpha$ Line Profiles in MaNGA Galaxy Pairs with FAST

Abstract

We present case studies comparing the global HI and H$\alpha$ 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 pre-merging, merging, and post-merger stages). We observe their global HI spectra with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), achieving a noise level of about 0.5 mJy. Five out of the six pair systems have secure detections of HI emissions (signal-to-noise ratio > 10). The HI fraction and star formation efficiency of the six pairs do not deviate from isolated galaxies. For the HI line profiles, common unique asymmetry is observed, indicating disturbances on the atomic gas from the galaxy interaction. The global H$\alpha$ 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 H$\alpha$ spectra tend to show multiple components in the pre-merger phase, and single component line profiles in the post-merger systems, while all HI spectra show single component line profiles regardless of merger stages. The HI and H$\alpha$ spectra show offsets in the central velocities, which appear to decrease from >100 km/s in the pre-merger pair to <10 km/s in post-merger pairs. This trend is consistent with the scenario that, despite the significantly different distribution and kinematics of the atomic and ionized gases, the merging process may contribute to the mixing and eventually align various gas contents.