Black hole mass and growth rate at high redshift

Abstract

We present new H- and K-band spectroscopy of 15 high-luminosity active galactic nuclei (AGNs) at redshifts 2.3Y3.4 obtained with Gemini South.We combined the data with spectra of an additional 29 high-luminosity sources to obtain a samplewith 1045:2 < kLk(5100 8) < 1047:3 ergs s 1 and a black hole (BH)mass range, using reverberation mapping relationships based on the H method, of 108.8Y1010.7 M .We do not find a correlation of L/LEdd with MBH, but we do find a correlation with kLk(5100 8), whichmight be due to selection effects. The L/LEdd distribution is broad and covers the range of 0.07Y1.6, similar to what is observed in lower redshift, lower luminosity AGNs.We suggest that this consistentlymeasured and calibrated sample gives the best representation of L/LEdd at those redshifts, and note potential discrepancies with recent theoretical and observational studies. The lower accretion rates are not in accordwith growth scenarios for BHs at such redshifts, and the growth times of many of the sources are longer than the age of the universe at the corresponding epochs. This suggests earlier episodes of faster growth at zk3 for those sources. The use of the C iv k1549 method gives considerably different results and a larger scatter; this method seems to be a poorMBH and L/LEdd estimator at very high luminosity.