Spectroscopy of broad absorption line quasars at $3\lesssim z \lesssim 5$ -- I: evidence for quasar winds shaping broad/narrow emission line regions

We present an observational study of 22 broad absorption line quasars (BAL QSOs) at $3\lesssim z \lesssim5$ based on optical/near-IR spectroscopy, aiming to investigate quasar winds and their effects. The near-IR spectroscopy covers the \hb\ and/or \mgii\ broad emission lines (BELs) for these quasars, allowing us to estimate their central black hole (BH) masses in a robust way. We found that our BAL QSOs on average do not have a higher Eddington ratio than that from non-BAL QSOs matched in redshift and/or luminosity. In a subset consisting of seven strong BAL QSOs possessing sub-relativistic BAL outflows, we see the prevalence of large \civ-BEL blueshift ($\sim$3100 km s$^{-1}$) and weak \oiii\ emission (particularly the narrow \oiii$\lambda$5007 component), indicative of nuclear outflows affecting the narrow emission-line (NEL) regions. In another subset consisting of thirteen BAL QSOs having simultaneous observations of \mgii\ and \hb, we found a strong correlation between 3000~\AA\ and 5000~\AA\ monochromatic luminosity, consistent with that from non-BAL QSOs matched in redshift and luminosity; however, there is no correlation between \mgii\ and \hb\ in FWHM, likely due to nuclear outflows influencing the BEL regions. Our spectroscopic investigations offer strong evidence that the presence of nuclear outflows plays an important role in shaping the BEL/NEL regions of these quasars and possibly, regulating the growth of central supermassive black holes (SMBHs). We propose that BEL blueshift and BAL could be different manifestations of the same outflow system viewed at different sightlines and/or phases.