There is ample evidence that the most significant growth epoch of the majority of super-massive black holes (SMBHs) must have occurred at z>1-2.
I will present our team's efforts to measure black hole masses and accretion rates in several high-redshift samples of AGNs, based on extensive NIR spectroscopic campaigns. I will particularly focus on a large sample of z~5 AGNs, which were observed in a combined VLT-Gemini campaign. This sample probes the most massive BHs at this epoch, but shows lower masses and higher accretion rates than those of z~2-3.5 sources. When combining these samples together, a clear evolutionary sequence is evident: the z~5 BHs grow through Eddington-limited accretion from a broad range of seed masses; their subsequent growth, at duty cycles of ~10-20%, forms the most massive BHs observed at z~2. I will also mention a few follow-up campaigns which aim at understanding the co-evolution of these BHs with their host galaxies.
