We present the results of a model-independent investigation of the rest-frame
UV spectra from a comprehensive sample of $394$ quasars in the redshift range
$1.5\leq z \leq 7.5$. We fit the main Broad Emission Lines (BELs) in the
rest-frame range $1280 \text{\AA} \leq \lambda \leq 3000 \text{\AA}$ (O I, C
II, Si IV, C III, C IV and Mg II) with a lightly-supervised spline fitting
technique. Redshifts are derived from the peaks of each fitted BEL and used to
compute relative velocity shifts. We show that our method gives unbiased
velocity shifts and is insensitive to spectral resolution and instrumental
parameters. It is found that the average blueshift of the \cfour\, line with
respect to several low-ionisation lines in luminosity-matched samples does not
significantly evolve over $1.5\gtrsim z\gtrsim6$. However, the average
blueshift increases significantly by a factor $\sim 2.5$ at $z\gtrsim 6$. We
propose that this redshift evolution can be explained by \cfour\, winds
launched perpendicularly to an accretion disk with increased torus opacity at
high-redshift, coupled with a potential orientation-driven selection bias. Our
results open new exciting avenues of investigation into young quasars in the
reionisation epoch.

对 394 个类星体的光谱进行模型无关的调查，发现随着红移的增加，类星体中 C IV 线的平均蓝移明显增加，这种演化可以用沿垂直于吸积盘的 C IV 风推演，并且可能受定向选择偏差的影响。