MIGHTEE-Hi: The relation between the Hi gas in galaxies and the cosmic web

Abstract

We study the 3D axis of rotation (3D spin) of 77 Hi galaxies from the MIGHTEE-Hi Early Science observations, and its relation to the filaments of the cosmic web. For this Hi-selected sample, the alignment between the spin axis and the closest filament (|cos 𝜓|) is higher for galaxies closer to the filaments, with h|cos 𝜓|i = 0.66 ± 0.04 for galaxies < 5 Mpc from their closest filament compared to h|cos 𝜓|i = 0.37±0.08 for galaxies at 5 < 𝑑 < 10 Mpc. We find that galaxies with a low Hi-to-stellar mass ratio (log10 (𝑀HI/𝑀★) < 0.11) are more aligned with their closest filaments, with h|cos 𝜓|i = 0.58 ± 0.04; whilst galaxies with (log10 (𝑀HI/𝑀★) > 0.11) tend to be mis-aligned, with h|cos 𝜓|i = 0.44 ± 0.04. We find tentative evidence that the spin axis of Hi-selected galaxies tend to be aligned with associated filaments (𝑑 < 10 Mpc), but this depends on the gas fractions. Galaxies that have accumulated more stellar mass compared to their gas mass tend towards stronger alignment.