  A search is performed for the process $pp \to G^* \to B_H\bar b/\bar B_H b
\to H b \bar b \to b\bar bb\bar b$, predicted in composite Higgs scenarios,
where $G^*$ is a heavy colour octet vector resonance and $B_H$ a vector-like
quark of charge $-1/3$. The data were obtained from $pp$ collisions at a
centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of
19.5 fb$^{-1}$, recorded by the ATLAS detector at the LHC. The largest
background, multijet production, is estimated using a data-driven method. No
significant excess of events with respect to Standard Model predictions is
observed, and upper limits on the production cross section times branching
ratio are set. Comparisons to the predictions from a specific benchmark model
are made, resulting in lower mass limits in the two-dimensional mass plane of
$m_{G^*}$ vs. $m_{B_H}$.
