it implies that the satellite galaxies are probably tracing the underlying smooth gas reservoir that is available for fuelling the central galaxies. If this hypothesis is true, the conformity behaviour should still hold when it is examined at low luminosity levels (i.e. by tracing the less bright satellites or clouds in the general environment that are potentially far more numerous than the brighter satellites).

Motivated by these results we perform a new analysis of the Bluedisk data. Our aim is to trace the faint gas distribution that may surround galaxies below the detection limit of the [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}data. Our method consists of adding up the flux of (both positive and negative) noise peaks in the [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}data cubes out to a radius of 16 arc min (typically 500 kpc), trying to detect a statistical [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}signal (i.e. an excess of positive detections) and studying whether its properties correlate with the [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}content of the central galaxy.

The paper is organised as follows. In section 2, we describe the Bluedisk data used in this analysis. In section 3, we introduce our new method to measure a total [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass in faint systems around primary galaxies through 