Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA - I. Catalogue in the Local Supercluster

Context. We present Hα3 (acronym for Hα − αα), an Hα narrow-band imaging survey of ∼400 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster. Aims. By using hydrogen recombination lines as a tracer of recent star formation, we aim to investigate the relationships between atomic neutral gas and newly formed stars in different environments (cluster and field), morphological types (spirals and dwarfs), and over a wide range of stellar masses (∼10 7.5 −10 11.5 M� ).