examining the noise peaks. In section 4, we discuss the origin of the [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass measured from an analysis of the noise peaks. We find that the excess [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass fraction in the primary galaxies is correlated with an excess [[H]{}[<span style="font-variant:small-caps;">i</span> ]{}]{}mass in the surrounding environment. In section 5, we discuss the implication of our results for cold mode gas accretion in galaxies. A $\Lambda$CDM cosmology with $\Omega_{m}=0.3$, $\Omega_{\lambda}=0.7$ and $h=0.7$ is assumed throughout the paper.

The sample
==========

The Bluedisk dataset
--------------------

The Bluedisk project aims at searching for clues about gas accretion and galactic disk formation in the local universe. Details about the sample, data processing and analysis can be found in Paper I and II, and here we only review the most relevant information.

The sample consists of 50 massive galaxies (M$_*>10^{10} \ms$) with a redshift between 0.018-0.03 (corresponding to a luminosity distance of 70-130 Mpc). From the atlas in Paper I, most of them are blue spiral galaxies. The target fields are covered by the Sloan Digital Sky Survey (SDSS, Abazajian et al. 2009), the Galaxy Evolution Explorer (GALEX) imaging survey (Martin et al. 2005), and the Wide-Field Infrared Survey Explorer (WISE, Wright 