27) with the lowest redshift, so that we have a narrow redshift range of 0.023–0.03 (a luminosity distance of 100-130 Mpc). We call these 40 target galaxies “primary galaxies”.

These galaxies have a broad distribution in [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass fraction $\fHI=\log \HIs$, ranging from lower than -2 to higher than 1 (Figure \[fig:sample\]). Compared to other samples featuring ${\rm H}{\textsc i}$-rich galaxies (like the samples from Lemonias et al. 2014 and the HIghMass project, High [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}Mass, Huang et al. 2014), the Bluedisk sample has the advantage of being able to compare the most [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}rich galaxies with those of normal [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}content. As we will show later in Section \[sec:conformity\], this is crucial for producing our main results.

As mentioned before, the aim of the paper is to investigate the connection between the [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}in the (central) primary galaxies and the [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}in the environment. In addition to $\fHI$, we also use a few other parameters to quantify the [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}richness of primary galaxies. Using the GALEX Arecibo SDSS Survey (GASS, Catinella et al. 2010), Catinella et al. (2013, [**C13 for short hereafter**]{}) calibrated a photometric estimator of $\fHI$ in galaxies with NUV$-r<4.5$ 