The Hα Dots Survey. IV. A Fourth List of Faint Emission-line Objects

Abstract We present the fourth catalog of serendipitously discovered compact extragalactic emission-line sources—H α Dots. A total of 454 newly discovered objects are included in the current survey list. These objects have been detected in searches of moderately deep narrowband images acquired for the ALFALFA H α project. The catalog of H α Dots presented in the current paper was derived from searches carried out using ALFALFA H α images obtained with the KPNO 2.1 m telescope. This results in a substantially deeper sample of Dots compared to our previous lists, which were all discovered in images taken with the WIYN 0.9 m telescope. The median R -band magnitude of the current catalog is 21.59, more than 1.6 mag fainter than the median for the 0.9 m sample (a factor of 4.4× fainter). Likewise, the median emission-line flux of the detected sources is a factor of 4.3× fainter. The line flux completeness limit of the current sample is ~3 × 10 −16 erg s −1 cm −2 . We present accurate coordinates, apparent magnitudes, and narrowband line fluxes for each object in the sample. Unlike our previous lists of H α Dots, the current sample does not include follow-up spectroscopy.