High-redshift quasars along the main sequence

Abstract

Context. The 4D Eigenvector 1 empirical formalism (4DE1) and its main sequence (MS) for quasars has emerged as a powerful tool for organising the diversity among quasar populations, as several key observational measures and physical parameters are systematically changing along it. Aims. Trends revealed by 4DE1 are very well established to explain all the diverse characteristics seen in low-redshift quasar samples. Nevertheless, the situation is far less clear when dealing with high-luminosity and high-redshift sources. Here, we aim to evaluate the behaviour of our sample of 22 quasars at high redshift (2.2 ≤ z ≤ 3.7) and high luminosity (47.39 ≤ L bol ≤ 48.36) in the context of the 4DE1. Methods. Our approach involves studying quasar physics through a spectroscopic exploration of UV and optical emission line diagnostics. We used new observations from the ISAAC instrument at ESO-VLT and primarily from the SDSS to cover the optical and the UV rest-frames, respectively. The emission lines were characterised both via a quantitative parametrisation of the line profiles and a decomposition of the emission line profiles using multicomponent fitting routines. Results. We provide spectrophotometric properties and line profile measurements for H β +[O III ] λλ 4959,5007, as well as Si IV λ 1397+O IV ] λ 1402, C IV λ 1549+He II λ 1640, and the 1900 Å blend (including Al III λ 1860, Si III ] λ 1892, and C III ] λ 1909). For six out of the 22 objects, a significantly blueshifted component on the H β profile is present. In 14 out of 22 cases, an H β outflowing component associated with [O III ] is detected. The majority of [O III ] λλ 4959,5007 emission line profiles show blueshifted velocities higher than 250 km s −1 . We find extremely broad [O III ] λλ 4959,5007 emission that is comparable to the width of H β broad profile in some highly accreting quasars. The [O III ] λλ 4959,5007 and C IV λ 1549 blueshifts show very high amplitudes and a high degree of correlation. The line widths and shifts are correlated for both [O III ] λλ 4959,5007 and C IV λ 1549, suggesting that emission from outflowing gas is providing a substantial broadening effect to both lines. Otherwise, the links between C IV λ 1549 centroid velocity at half intensity ( c (1/2)), Eddington ratio ( L / L Edd ), and bolometric luminosity are found to be in agreement with previous studies of high-luminosity quasars. Conclusions. Our analysis suggests that the behaviour of quasars of very high luminosity all along the main sequence is strongly affected by powerful outflows involving a broad range of spatial scales. The main sequence correlations remain valid at high redshift and high luminosity even if a systematic increase in line width is observed. Scaling laws based on UV Al III λ 1860 and H β emission lines are equally reliable estimators of M BH .

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