Discovery of two broad absorption line quasars at redshift about 4.75 using the Lijiang 2.4m telescope

TL;DR

This paper reports the discovery of two luminous broad absorption line quasars at redshift about 4.75 using the Lijiang 2.4m telescope, with one potentially having the highest absorption index recorded, providing insights into AGN feedback.

Contribution

The study presents the first identification of two high-redshift BAL quasars with one possibly exhibiting the highest absorption index, expanding understanding of quasar outflows and AGN feedback at early cosmic times.

Findings

Discovered two BAL quasars at z~4.75.

One quasar may have the highest absorption index recorded.

Deep, broad absorption lines indicate sub-relativistic outflows.

Abstract

The ultraviolet broad absorption lines have been seen in the spectra of quasars at high redshift, and are generally considered to be caused by outflows with velocities from thousands kilometers per second to one tenth of the speed of light. They provide crucial implications for the cosmological structures and physical evolutions related to the feedback of active galactic nuclei (AGNs). Recently, through a dedicated program of optically spectroscopic identifications of selected quasar candidates at redshift 5 by using the Lijiang 2.4 m telescope, we discovered two luminous broad absorption line quasars (BALQSOs) at redshift about 4.75. One of them may even have the potentially highest absorption Balnicity Index (BI) ever found to date, which is remarkably characterized by its deep, broad absorption lines and sub-relativistic outflows. Further physical properties, including the metal abundances, variabilities, evolutions of the supermassive black holes (SMBH) and accretion disks associated with the feedback process, can be investigated with multi-wavelength follow-up observations in the future.