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

Abstract

We present the second catalog of serendipitously discovered compact extragalactic emission-line sources -- H$\alpha$ Dots. These objects have been discovered in searches of moderately deep narrow-band images acquired for the ALFALFA H$\alpha$ project (Van Sistine et al. 2016). In addition to cataloging 119 new H$\alpha$ Dots, we also present follow-up spectral data for the full sample. These spectra allow us to confirm the nature of these objects as true extragalactic emission-line objects, to classify them in terms of activity type (star forming or AGN), and to identify the emission line via which they were discovered. We tabulate photometric and spectroscopic data for the all objects, and present an overview of the properties of the full H$\alpha$ Dot sample. The H$\alpha$ Dots represent a broad range of star-forming and active galaxies detected via several different emission lines over a wide range of redshifts. The sample includes H$\alpha$-detected blue compact dwarf galaxies at low redshift, [\ion{O}{3}]-detected Seyfert 2 and Green Pea-like galaxies at intermediate redshifts, and QSOs detected via one of several UV emission lines, including Ly$\alpha$. Despite the heterogeneous appearance of the resulting catalog of objects, we show that our selection method leads to well-defined samples of specific classes of emission-line objects with properties that allow for statistical studies of each class.