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.

Accepted for publication in the Astronomical Journal

References in corpus (5)

• Lyman-alpha spectral properties of five newly discovered Lyman continuum emitters
• Diverse properties of Ly-alpha emission in low-redshift compact star-forming galaxies with extremely high [OIII]/[OII] ratios
• Kinematics and Optical Depth in the Green Peas: Suppressed Superwinds in Candidate LyC Emitters
• Chemical abundances of Seyfert 2 AGNs $-$II. N2 metallicity calibration based on SDSS
• Properties of the KISS Green Pea Galaxies

Cited by in corpus (8)

• J-PLUS: Uncovering a large population of extreme [OIII] emitters in the local Universe
• Hα Dots: Direct-Method Metal Abundances of Low-Luminosity Star-Forming Systems
• Star Formation in Outer Rings of S0 galaxies. V. UGC 4599 -- an S0 with gas probably accreted from a filament
• The Star Formation Across Cosmic Time (SFACT) Survey. I. Survey Description and Early Results from a New Narrow-Band Emission-Line Galaxy Survey
• Properties of the Lowest Metallicity Galaxies Over the Redshift Range z = 0.2 to z = 1
• The H$\alpha$ Dots Survey. IV. A Fourth List of Faint Emission-Line Objects
• Extreme Emission-Line Galaxies in the MUSE Hubble Ultra Deep Field Survey
• Searches for Extremely Metal Poor Galaxies using ALFALFA-selected Dwarf Galaxies