Discovery of a hyperluminous quasar at z = 1.62 with Eddington ratio >3 in the eFEDS field confirmed by KOOLS-IFU on Seimei Telescope

We report the discovery of a hyperluminous type 1 quasar (eFEDS J082826.9-013911; eFEDS J0828-0139) at zspec = 1.622 with a super-Eddington ratio (λ Edd). We perform the optical spectroscopic observations with KOOLS-IFU (the Kyoto Okayama Optical Low-dispersion Spectrograph with optical fiber) on the Seimei Telescope. The black hole mass (MBH) based on the single-epoch method with Mg iiλ2798 is estimated to be MBH = (6.2 ± 1.2) × 10⁸\, M. To measure the precise infrared luminosity (LIR), we obtain submillimeter data taken by SCUBA-2 on the James Clerk Maxwell Telescope and conduct the spectral energy distribution analysis with X-ray to submillimeter data. We find that LIR of eFEDS J0828-0139 is LIR = (6.8 ± 1.8) × 10¹³\, L, confirming the existence of a hypeluminous infrared galaxy. λ Edd is estimated to be λ Edd = 3.6 ± 0.7, making it a quasar with one of the highest BH mass accretion rates at cosmic noon.