The loneliest galaxies in the Universe: a GAMA and Galaxy Zoo study on void galaxy morphology

Abstract

ABSTRACT The large-scale structure of the Universe is comprised of galaxy filaments, tendrils, and voids. The majority of the Universe’s volume is taken up by these voids, which exist as underdense, but not empty, regions. The galaxies found inside these voids are expected to be some of the most isolated objects in the Universe. This study, using the Galaxy and Mass Assembly (GAMA) and Galaxy Zoo surveys, aims to investigate basic physical properties and morphology of void galaxies versus field (filament and tendril) galaxies. We use void galaxies with stellar masses ($M_*$) of 109.35 M⊙ < M* < 1011.25 M⊙, and this sample is split by identifying two redshift-limited regions, 0 < z < 0.075 and 0.075 < z < 0.15. To find comparable objects in the sample of field galaxies from GAMA and Galaxy Zoo, we identify ‘twins’ of void galaxies as field galaxies within ±0.05 and ±0.15 dex of $M_*$ and specific star formation rate. We determine the statistical significance of our results using the Kolmogorov–Smirnov test. We see that void galaxies, in contrast with field galaxies, seem to be disc-dominated and have predominantly round bulges (with >50 per cent of the Galaxy Zoo citizen scientists agreeing that bulges are present).