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

Abstract

We present our first results of the survey for high redshift quasars at $5\lesssim \mathrm{z}\lesssim 5.7$. 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 $\le$ z $\le$ 5.40 and 5.50 $\le$ z $\le$ 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 $\le$ z $\le$ 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.

16 pages, 12 figures, and 9 tables. Accepted for publication in ApJS