Ting-Yi Lu (NTHU), Tomotsugu Goto (NTHU)
Lya transmission in the Gunn-Peterson troughs (GP trough) of high redshift quasars is one of the most powerful probes for revealing the cosmic reionization history. The transmission along the line-of-sights (LOSs) toward quasars directly traces the fractional change of neutral intergalactic medium (IGM) with redshift. Several studies have shown that the transmission goes down to zero at z~6, which implies the end stage of the cosmic reionization. However, there is still a large variation of the transmission. So far, only less than two hundred of luminous quasars (M1450>-24.5) are found at z>6 and not all of them are analysed. The variation due to the limited amount of the known quasars and the inhomogeneous process of the reionization could be averaged out by adding more sample. We present the measurements on 64 quasars found from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project based on the multi-band photometry data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) survey. The 64 quasars are at 6.90>z>5.84 and with -21.5>M1450>-26.5. We use the Principle Component Analysis (PCA) to fit the continua and predict the intrinsic spectra redward of the Lya emission line. We extend the transmission measurement to z~6.8. Furthermore, taking the advantage that PCA gives a better prediction of the intrinsic spectrum around the Lya emission line, we measure the near zone regions and the damping wings of the quasars, which could be used on revealing the neutral fraction around the quasars.