Searching for Dark Galaxies with HI detection from the Arecibo Legacy Fast ALFA (ALFALFA) survey

TL;DR

This paper presents a catalog of 142 dark galaxy candidates identified from the ALFALFA survey, using multi-wavelength imaging and careful exclusion criteria to find HI sources without optical counterparts, aiding the study of dark matter in galaxy formation.

Contribution

The study provides the first extensive catalog of dark galaxy candidates from ALFALFA, with detailed analysis of their properties and environment, advancing understanding of dark matter's role in galaxy evolution.

Findings

Dark galaxy candidates have smaller dynamical masses.

They exhibit higher HI-to-dynamical mass ratios.

Candidates are found in less dense regions than luminous galaxies.

Abstract

We present a catalog of 142 dark galaxy candidates in a region covered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We start with 344 ALFALFA HI sources without optical counterparts and remove those that do not seem to have dark galaxy origin. To do that, we first eliminate 83 sources that are known HI clouds probably formed from tidal interactions between galaxies and 13 sources that have optical counterparts. We then remove 56 sources located near other HI sources, which are likely to be HI clouds. We further exclude 10 sources that have nearby HI sources within the ALFALFA beam and 40 sources potentially associated with nearby galaxies. We perform visual inspection of optical images from DESI Legacy Imaging Survey with an $r$-band surface brightness limit of $\sim 28.5 \rm \ mag\ arcsec^{-2}$ as well as NUV images from GALEX to confirm the absence of stellar emission. We additionally inspect infrared images from WISE and AKARI for dust emission. As a result, we identify 142 dark galaxy candidates and analyze their physical properties by comparing with luminous galaxies. We find that the dark galaxy candidates generally have smaller dynamical masses, higher HI-to-dynamical mass ratios, and are located in less dense regions when compared to luminous galaxies, which is consistent with results from cosmological simulations. This sample provides an important testbed for studying the role of dark matter in galaxy formation and evolution.