Poster Presentation

Discovery of high-z quasars using medium-band observations

Author(s): Suhyun Shin(SNU), Myungshin Im(SNU), Minhee Hyun(SNU), Yongjung Kim(SNU), and IMS team

Presenter: Suhyun Shin (Seoul National University)

The universe has been ionized in the post-reionization by several photon-contributors. The main source to produce the hydrogen ionizing photons is not revealed so far. Faint quasars have been expected to generate UV photon budgets required to maintain ionization state of universe. Observational limits, however, hinder to discover them despite their higher number density than bright one. Consequently, the influence of faint quasars on the post-reionization are not considered sufficiently. Therefore, a survey to find faint quasars at z ~ 5 is crucial to determine the main ionizing source in the post-reionization era. Deep images from the Hyper Suprime-Cam Subaru Strategic Program(HSC SSP) allow us to search for quasars with low luminosities in the ELAIS-N1 field. J band information are acquired by the Infrared Medium-deep Survey (IMS) and the UKIRT Infrared Deep Sky Survey (UKIDSS) – Deep Extragalactic Survey (DXS). Faint quasar candidates were selected from several multi-band color cut criteria based on simulated quasars on color-color diagram. To choose the reliable candidates with possible Lyman break, medium-bands observations were performed. Whether a candidate is a quasar or a dwarf contamination was decided by results from chi-square minimization of quasar/dwarf model fitting. Spectroscopic follow-up observations confirm three quasars at z ~ 5. 100% spectral confirmation success rate implies that the medium-band observations effectively select faint quasars with strong Lyman alpha emission.