line emission. They are therefore included in our present study.

![image](histo_redshifts.jpg){width="48.00000%"} ![image](histo_radiopower.jpg){width="48.00000%"}

The targets are taken from a number of different catalogs, including the Molonglo Reference Catalog [@large81], the 3$^{{\rm
    rd}}$, 4$^{{\rm th}}$, and 5$^{{\rm th}}$ Cambridge Catalogs [@laing83; @pilkington65; @pearson75], the Parkes [@wright90], Parkes-MIT-NRAO [PMN  @griffith93] and Texas [TXS, @douglas96] surveys, the catalog of Ultra-Steep-Spectrum radio sources [USS; @debreuck00], and the Sydney University Molonglo Sky Survey [SUMSS @mauch03]. Our sample is therefore not complete in a statistical sense, however, given the rarity of powerful high-redshift radio galaxies, it would not be practical to collect a significant number of sources from a statistically complete sample. Moreover, we wish to study trends in gas properties as a function of the radio size and radio power, so that a uniform sampling of radio properties is more important than matching the radio luminosity function. For a population study this would of course be different. In a general sense, these galaxies were selected for their steep spectral indices from low-frequency radio surveys. All had known spectroscopic redshifts, typically from rest-frame UV observations [most redshifts were taken from @debreuck00], which implies that our sample is biased towards galaxies with bright UV or optical line emission. 