# The Infrared Medium-deep Survey. III. Survey of Luminous Quasars at 4.7 $\leq$ z $\leq$ 5.4

## TL;DR

This study reports the discovery of seven luminous quasars at redshifts 4.7 to 5.4 using a novel multi-wavelength filter technique, providing insights into black hole growth during early cosmic epochs.

## Contribution

It introduces a new selection method with custom filters that effectively reduces interloper contamination in high-redshift quasar surveys.

## Key findings

- Seven quasars confirmed at 4.7 ≤ z ≤ 5.4.
- Quasars are accreting near the Eddington limit.
- Supports rapid black hole growth at high redshift.

## Abstract

We present our first results of the survey for high redshift quasars at $5 \lesssim {\rm z} \lesssim 5.7$. The search for quasars in this redshift range has been known to be challenging due to limitations of filter sets used in previous studies. We conducted a quasar survey for two specific redshift ranges, 4.60 $\leq$ z $\leq$ 5.40 and 5.50 $\leq$ z $\leq$ 6.05, using multi-wavelength data that include observations using custom-designed filters, $is$ and $iz$. Using these filters and a new selection technique, we were able to reduce the fraction of interlopers. Through optical spectroscopy, we confirmed seven quasars at 4.7 $\leq$ z $\leq$ 5.4 with $-27.4 < M_{1450} < -26.4$ which were discovered independently by another group recently. We estimated black hole masses and Eddington ratios of four of these quasars from optical and near-infrared spectra, and found that these quasars are undergoing nearly Eddington-limited accretion which is consistent with the rapid growth of supermassive black holes in luminous quasars at z $\sim$ 5.