tokens: by scaling relations between the H i content and other intrinsic properties of galaxies. These H i scaling relations can be useful in identifying galaxies that have either more H i than expected or less H i than expected, as galaxies like these may have been affected by recent processes including the removal or accretion of gas. One way to characterize the H i gas content of galaxies is with H i deficiency. H i deficiency is the logarithmic difference between the observed H i mass and the expected H i mass: where M H i exp is the expected H i mass calculated from scaling relations, and M H i obs is the measured H i mass taken from observations (Haynes Giovanelli 1984 ). Generally, a galaxy is considered to have a normal H i gas content if its H i deficiency is between −0.3 and 0.3 (Dénes, Kilborn Koribalski 2014 ), with an H i excess if −0.3 and H i deficiency if >0.3. Studies use H i -selected samples combined with SDSS optical properties to derive scaling relations. With the GASS survey, Catinella et al. ( 2012 ) found that a good predictor of the H i content is the linear combination of stellar surface density and NUV− r colour. We examine the H i deficiency of our sample adapting results using the H i to stellar mass fraction function shown in fig. 8 from Catinella et al. ( 2012 ): with a = −0.285, b = −0.366, and c = 2.872. This function is the relation between H i mass fraction and a linear combination of stellar mass surface density and NUV − r colour with the relation obtained using the subset galaxies with NUV − r ≤ 4.5 mag. The stellar mass surface density is calculated from the formula where R 50 z is the radius containing 50 per cent of the Petrosian flux in z- band from SDSS DR7, and NUV − r is the GALEX (Martin et al. 2005 ) NUV magnitude minus the SDSS DR7 r -band magnitude. Figure 8. H i deficiency using scaling relations from Catinella et al. ( 2012 ). A solid grey line is drawn for deficiency = 0 and a dotted grey line for deficiency = +0.3 and −0.3. Fig. 8(a) shows the H i deficiency in relation to the log of stellar mass. Fig. 8(b) shows the H i deficiency in relation to the distance from filamentary structure based on the DisPeSE topological algorithm. Open symbols are small galaxies with uncertain stellar masses. The results for H i deficiency are shown in Fig. 8 . A solid grey line is drawn for deficiency = 0 and a dotted grey line for deficiency = +0.3 and −0.3. Figs 8(a) and (b) show the H i deficiency in relation to stellar mass and distance to filament, with no obvious trends. In Catinella et al. ( 2012 ), the results are for a sample of galaxies with stellar mass greater than 10 10 M ⊙ . Since only three galaxies (1204837, 1437568, 969633) are above stellar mass 10 10 M ⊙ , this method is not well calibrated for our lower mass sample. With that said, none of the galaxies are H i deficient and half of the sample has H i excess. This is of course not surprising for a small H i -selected sample. 4.3 H <sc>i</sc>
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