Abstract

We present a fourth catalog of H I sources from the Arecibo Legacy Fast ALFA (ALFALFA) Survey. We report 541 detections over 136 deg2, within the region of the sky having 22h < α < 03h and 24° < δ < 26°. This complements a previous catalog in the region 26° < δ < 28°. We present here the detections falling into three classes: (1) extragalactic sources with signal-to-noise ratio (S/N)>6.5, where the reliability of the catalog is better than 95%; (2) extragalactic sources 5.0 < S/N < 6.5 and a previously measured optical redshift that corroborates our detection; or (3) High Velocity Clouds (HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of the 541 objects presented here, 90 are associated with HVCs, while the remaining 451 are identified as extragalactic objects. Optical counterparts have been matched with all but one of the extragalactic objects.