Speaker
Description
Twenty or more narrow-line (FWHM<500 km/s) quasars have been discovered through the high-z quasar search project SHELLQs, based on the Subaru HSC Survey. Their narrow but luminous Ly_alpha make them good candidates of obscured quasars at z > 6, that are expected to be abundant. Besides the discovery spectra in the rest-frame UV band, JWST-NIRSpec data of 9 objects have been acquired during the Cycle-2. Many of these spectra exhibit broad Balmer emission at the base of narrow lines, similar to the fainter JWST-selected AGN. We selected four objects as promising obscured quasar candidates that are characterised by exceptionally faint UV continuum and large Ly_alpha luminosity exceeding 10^44 erg/s to observed with Chandra. However, these X-ray observations resulted in no detection in the rest-frame 7-35 keV band, placing them in the X-ray faint regime. If heavy obscuration plays a role, it should occur at inner regions, given small Balmer decrements seen in narrow lines of the JWST spectra. Along with other possible explanations, we consider supercritical accretion for the high-z quasar population and, due to the inherent anisotropy of radiation in the supercritical accretion flow at innermost radii, the X-ray faintness of our SHELLQs narrow-line quasars might arise from an orientation effect.
