ALFALFA survey: the {alpha}.40 HI source catalog

Covering 40% of the final survey area, the {alpha}.40 catalog contains 15855 sources in the regions 07h30m<RA<16h30m, +04{deg}<DEC<+16{deg}, and +24{deg}<DEC<+28{deg} and 22h<RA<03h, +14{deg}<DEC<+16{deg}, and +24{deg}<DEC<+32{deg}. Of those, 15041 are certainly extragalactic, yielding a source density of 5.3 galaxies per deg^2^, a factor of 29 improvement over the catalog extracted from the HI Parkes All-Sky Survey.

In addition to the source centroid positions, HI line flux densities, recessional velocities, and line widths, the catalog includes the coordinates of the most probable optical counterpart of each HI line detection, and a separate compilation provides a cross-match to identifications given in the photometric and spectroscopic catalogs associated with the Sloan Digital Sky Survey Data Release 7. Fewer than 2% of the extragalactic HI line sources cannot be identified with a feasible optical counterpart; some of those may be rare OH megamasers at 0.16<z<0.25.