The H$\alpha$ Dots Survey. IV. A Fourth List of Faint Emission-Line Objects

TL;DR

This paper introduces a new, deeper catalog of 454 faint extragalactic emission-line objects called Hα Dots, discovered using the KPNO 2.1 m telescope, extending previous surveys with fainter objects and more precise data.

Contribution

It provides the fourth catalog of Hα Dots, significantly expanding the sample with deeper observations and more detailed measurements without follow-up spectroscopy.

Findings

Catalog includes 454 new objects with median R-band magnitude 21.59

Sample is more than 1.6 magnitudes fainter than previous lists

Line-flux completeness limit is approximately 3 x 10$^{-16}$ erg/s/cm$^2$

Abstract

We present the fourth catalog of serendipitously discovered compact extragalactic emission-line sources -- H$\alpha$ 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 narrow-band images acquired for the ALFALFA H$\alpha$ project (Van Sistine et al. 2016). The catalog of H-alpha Dots presented in the current paper was derived from searches carried out using ALFALFA H$\alpha$ 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 magnitudes fainter than the median for the 0.9~m sample (factor of 4.4x fainter). Likewise, the median emission-line flux of the detected sources is a factor of 4.3x fainter. The line-flux completeness limit of the current sample is approximately 3 x 10$^{-16}$ erg/s/cm$^2$. We present accurate coordinates, apparent magnitudes and narrow-band line fluxes for each object in the sample. Unlike our previous lists of H$\alpha$ Dots, the current sample does not include follow-up spectroscopy.