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Newly Discovered z ~ 5 Quasars Based on Deep Learning and Bayesian Information Criterion
신수현,임명신,김용정,Linhua Jiang 한국천문학회 2022 Journal of The Korean Astronomical Society Vol.55 No.4
We report the discovery of four quasars with $M_{1450} \gtrsim -25.0$ mag at z ~ 5 and supermassive black hole mass measurement for one of the quasars. They were selected as promising high-redshift quasar candidates via deep learning and Bayesian information criterion, which are expected to be effective in discriminating quasars from the late-type stars and high-redshift galaxies. The candidates were observed by the Double Spectrograph on the Palomar 200-inch Hale Telescope. They show clear Ly$\alpha$ breaks at about 7000--8000 \AA, indicating they are quasars at $4.7 < z < 5.6$. For HSC J233107-001014, we measure the mass of its supermassive black hole (SMBH) using its C IV $\lambda 1549$ emission line. The SMBH mass and Eddington ratio of the quasar are found to be ~10$^8 M_{\odot}$ and ~0.6, respectively. This suggests that this quasar possibly harbors a fast growing SMBH near the Eddington limit despite its faintness ($L_{\rm Bol} < 10^{46} $erg\,s$^{-1}$). Our 100\% quasar identification rate supports high efficiency of our deep learning and Bayesian information criterion selection method, which can be applied to future surveys to increase high-redshift quasar sample.