  We report evidence that the gas properties of X-ray groups containing radio
galaxies differ from those of radio-quiet groups. For a well-studied sample of
ROSAT-observed groups, we found that more than half of the elliptical-dominated
groups can be considered ``radio-loud'', and that radio-loud groups are likely
to be hotter at a given X-ray luminosity than radio-quiet groups. We tested
three different models for the origin of the effect and conclude that
radio-source heating is the most likely explanation. We found several examples
of groups where there is strong evidence from Chandra or XMM-Newton images for
interactions between the radio source and the group gas. A variety of
radio-source heating processes are important, including shock-heating by young
sources and gentler heating by larger sources. The heating effects can be
longer-lasting than the radio emission. We show that the sample of X-ray groups
used in our study is not significantly biased in the fraction of radio-loud
groups that it contains. This allows us to conclude that the energy per
particle that low-power radio galaxies can inject over the group lifetime is
comparable to the requirements of structure formation models.
