THE VOID GALAXY SURVEY: OPTICAL PROPERTIES AND H I MORPHOLOGY AND KINEMATICS

We have carefully selected a sample of 60 galaxies that reside in the deepest underdensities of geometrically identified voids within the Sloan Digital Sky Survey. H I imaging of 55 galaxies with the Westerbork Synthesis Radio Telescope reveals morphological and kinematic signatures of ongoing interactions and gas accretion. We probe a total volume of 485 Mpc3 within the voids, with an angular resolution of 8 kpc at an average distance of 85 Mpc. We reach column density sensitivities of 5 × 1019 cm–2, corresponding to an H I mass limit of 3 × 108 M☉. We detect H I in 41 galaxies, with total masses ranging from 1.7 × 108 to 5.5 × 109 M☉. The upper limits on the 14 non-detections are not inconsistent with their luminosities, given their expected H I mass-to-light ratios. We find that the void galaxies are generally gas-rich, low-luminosity, blue disk galaxies, with optical and H I properties that are not unusual for their luminosity and morphology. The sample spans a range of absolute magnitudes (–16.1 > Mr > –20.4) and colors (0.06 <g – r < 0.87), and includes disk and irregular galaxies. We also identify three as early-type galaxies, all of which are not detected in H I. All galaxies have stellar masses less than 3 × 1010 M☉, and many have kinematic and morphological signs of ongoing gas accretion, suggesting that the void galaxy population is still in the process of assembling. The small-scale clustering in the void, within 600 kpc and 200 km s–1, is similar to that in higher density regions, and we identify 18 H I-rich neighboring galaxies in the voids. Most are within 100 kpc and 100 km s–1 of the targeted galaxy, and we find no significant population of H I-rich low-luminosity galaxies filling the voids, contrary to what is predicted by simulations.