lie outside the beam but within 250 km s$^{-1}$. We then estimate the HI radius of each companion, using the relationship between HI mass and diameter reported in Wang et al. (2016)[^1] If a companion’s estimated HI radius overlaps the beam, we remove the given host galaxy from our training set. An additional 50 galaxies are removed from our training set by this criterion, leaving a training set of 6329 galaxies whose HI fluxes are unlikely to be contaminated by neighbouring galaxies. Visual inspection of the SDSS images of a random subset of these galaxies confirms this interpretation, as no obvious blue galaxies are seen within one beam radius (with the exception of those with relative velocities greater than 250 km s$^{-1}$).

Additional Samples and Ancillary Data
-------------------------------------

In order to test our  estimator on independent datasets, we will also make use of several other samples that have been matched with the SDSS. The largest of these is the GASS sample[^2], for which we use the 342 detections from the data release 3 (Catinella et al. 2013). Additionally, we use the Cornell catalog ($\sim 30$ galaxies, Giovanelli et al 2007) as incorporated into the GASS representative sample and a sample 