A Preliminary Search for RELHIC Candidates in the ALFALFA α.100 Catalogue: Cloud-9 Analogues and Optical Counterpart Screening

This research presents a preliminary search for Reionization-Limited H I Clouds (RELHICs) using the ALFALFA α.100 catalogue, with the recently reported Cloud-9 object serving as the primary reference. The study applies selection criteria based on H I line width, detection reliability, optical identification, and heliocentric velocity to identify potential Cloud-9 analogues. Following catalogue filtering, 47 sources were initially selected, of which eight passed the velocity criteria. These eight sources were subsequently examined using Legacy Survey DR10 optical images. Two sources, AGC 189207 and AGC 749241, were identified as preliminary candidates for further investigation. However, neither object can currently be confirmed as a RELHIC due to limitations in optical imaging depth and the lack of sufficient observational evidence. This work documents the selection methodology, candidate screening process, comparison with Cloud-9, observational limitations, and recommended follow-up observations using deeper optical imaging (HST/JWST) and interferometric H I observations. The results provide a preliminary candidate list and a reproducible framework for further searches for starless H I clouds.