Neutral hydrogen in isolated galaxies. IV. Results for the Arecibo sample.

A standard sample for the comparison of the H I content of galaxies in various intergalactic environments is presently defined by means of observations of 324 isolated galaxies lying in the declination range accessible to the Arecibo 305-m telescope. Both mapping and single point spectra are used to compute the integral properties of these galaxies. Neutral hydrogen was detected in 288 of the 324 galaxies surveyed, and it is noted that the optical diameter of a spiral disk is better correlated with the hydrogen mass than the morphological type. When used to define a measure of H I content, the isolated galaxy sample can predict 'normalcy' with an accuracy that carries a standard error of about 0.20 in the log of the H I mass, if a dependence on disk size, as well as type, is taken into account.