The Arecibo Legacy Fast ALFA Survey: The ALFALFA Extragalactic HI Source Catalog.

We present the catalog of ~31500 extragalactic HI line sourcesdetected by the completed ALFALFA survey out to z 6.5) detections and ones of lower quality which coincide in both position and recessional velocitywith galaxies of known redshift. We review the observing technique, data reductionpipeline, and catalog construction process, focusing on details of particular relevance to understanding the catalog's compiled parameters. We further describe and make available the digital HI line spectra associated with the catalogued sources. In addition to the extragalactic HI line detections, we report nine confirmed OH megamasersand ten OH megamasercandidates at 0.16 < z < 0.22 whose OH line signalsare redshifted into the ALFALFA frequency band. Because of complexities in data collection and processing associated with the use of a feed-hornarray on a complex single-dish antenna in the terrestrial radio frequency interference environment, we also present a list of suggestions and caveats for consideration by users of the ALFALFA extragalactic catalog for future scientific investigations.