Understanding the evolution of accretion activity is fundamental to our understanding of how galaxies form and evolve over the history of the Universe .
We analyse a complete sample of 27 radio galaxies which includes both high-excitation ( HEGs ) and low excitation galaxies ( LEGs ) , spanning a narrow redshift range of 0.9 < z < 1.1 and covering a factor of \sim 1000 in radio luminosity .
Using data from the Spitzer Space Telescope combined with ground-based optical and near-infrared imaging , we show that the host galaxies have masses in the range of 10.7 < \log _ { 10 } ( M / M _ { \odot } ) < 12.0 with HEGs and LEGs exhibiting no difference in their mass distributions .
We also find that HEGs accrete at significantly higher rates than LEGs , with the HEG/LEG division lying at an Eddington ratio of \lambda \sim 0.04 , which is in excellent agreement with theoretical predictions of where the accretion rate becomes radiatively inefficient , thus supporting the idea of HEGs and LEGs being powered by different modes of accretion .
Our study also shows that at least up to L _ { 151 MHz } \sim 3 \times 10 ^ { 27 } W Hz ^ { -1 } sr ^ { -1 } , HEGs and LEGs are indistinguishable in terms of their radio properties .
From this result we infer that , at least for the lower radio luminosity range , another factor besides accretion rate must play an important role in the process of triggering jet activity .