underlying extended reservoir of cold gas. If this hypothesis is correct, we expect to detect conformity also at lower [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass levels than probed by E. Wang et al. (2015), in a regime dominated by very faint satellite galaxies and$\slash$or gas clouds in the inter-galactic medium. In this section we introduce our technique to detect this faint [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}gas, in the environment of the Bluedisk galaxies.

The method entails an analysis of the noise peaks (both positive and negative) in [**the cleaned data cubes**]{} in order to obtain a statistical detection. Because the noise is distributed symmetrically around 0 (both the median and mean background of a cube are typically within $\pm$10$^{-5}$ mJy beam$^{-1}$, while the rms of a cube is $\sim$0.4 mJy beam$^{-1}$), a positive noise peak will statistically be cancelled out by a negative noise peak of the same level. If in addition to noise there is a collection of very faint [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}objects, then these will add a slight positive signal to the noise, that will elevate the positive noise peaks or diminish negatiive noise peaks. This bias is detectable by a careful analysis of the distribution of the noise values throughout the cube. 