following tests.

We calculate the sum of all positive voxels belonging to candidates and the absolute sum of all the negative voxels belonging to candidates, and we refer to them as $f+_{cand}$ and $f-_{cand}$. We calculate the total flux in the reliable sources and the total flux in the candidates, and refer to these as $f_{rel}$ and $f_{cand}$ respectively. We calculate $f+_{cand}$, $f-_{cand}$, $f_{cand}$ and $f_{rel}$ for each channel map within 500 km$/$s from the systemic velocity and 500 kpc from the position of the primary galaxy. These are the velocity range and sky region within which we perform our analysis. The top row of Figure \[fig:error\_cleaning\] shows that there is no correlation between $f-_{cand}$ and $f_{rel}$, suggesting that clean residuals do not significantly affect the noise (negative voxels) of the data cube. There is a very weak relation between $f+_{cand}$ and $f_{rel}$, resulting in a systematic linear relation of $f_{cand}$ increasing slightly as a function of $f_{rel}$. We argue that part of the relation reflects galaxy-environment connections rather than artefacts, as we will show later. If we attribute the relation fully to clean artefacts around reliable sources, on average an [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass of 0.11$\times10^8\ms$ related to clean artefacts 