SIMBAD references

We analyse several large samples of active galactic nuclei (AGNs) in order to establish the best tools required to study the evolution of black hole mass (M_BH) and normalized accretion rate (L/L_Edd). The data include spectra from the Sloan Digital Sky Survey, 2dF QSO Redshift survey and 2dF SDSS LRG And QSO survey public surveys at z < 2, and a compilation of smaller samples with 0 < z < 5. We critically evaluate the usage of the MgIIλ2798 and CIVλ1549 lines, and adjacent continuum bands, as estimators of M_BH and L/L_Edd, by focusing on sources where one of these lines is observed together with Hβ. We present a new, luminosity-dependent bolometric correction for the monochromatic luminosity at 3000Å, L₃₀₀₀, which is lower by a factor of ∼ 1.75 than those used in previous studies. We also re-calibrate the use of L₃₀₀₀ as an indicator for the size of the broad emission-line region (R_BLR) and find that \mi R\mi BLR prop.to\mi L\mn 3000\mn 0.62, in agreement with previous results. We find that \mi FWHM \mo (\mi Mg\mi i\mi i\mo)∼ \mi FWHM=(\mi Hbeta=) for all sources with \mi FWHM=(\mi Mg\mi i\mi i=)=<∼ \mn 6000\mspace \mspace\mi km\mspace\mi s=–\mn 1. Beyond this full width at half-maximum (FWHM), the MgII line width seems to saturate. The spectral region of the MgII line can thus be used to reproduce Hβ-based estimates of M_BH and L/L_Edd, with negligible systematic differences and a scatter of ∼ 0.3dex. The width of the CIV line, on the other hand, shows no correlation with either that of the Hβ or the MgII lines and we could not identify the reason for this discrepancy. The scatter of M_BH(CIV), relative to M_BH(Hβ), is of almost 0.5dex. Moreover, 46per cent of the sources have \mi FWHM=(\mi C\mspace \mi i\mi v=)=<∼ \mi FWHM=(\mi Hbeta=), in contrast with the basic premise of the virial method, which predicts \mi FWHM=(\mi C\mspace\mi i\mi v=)=/\mi FWHM=(\mi Hbeta=)=≃ \mn 3.7, based on reverberation mapping experiments. This fundamental discrepancy cannot be corrected based on the continuum slope or any CIV-related observable. Thus, the CIV line cannot be used to obtain precise estimates of M_BH. We conclude by presenting the observed evolution of M_BH and L/L_Eddwith cosmic epoch. The steep rise of L/L_Edd with redshift up to z ≃ 1 flattens towards the expected maximal value of L/L_Edd ≃ 1, with lower M_BH sources showing higher values of L/L_Eddat all redshifts. These trends will be further analysed in a forthcoming paper.