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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.
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