Detections of [OIII] 88 $\mu$m in Two Quasars in the Reionization Epoch

With the Atacama Large Millimeter/sub-millimeter Array (ALMA), we report detections of the far-infrared (FIR) [OIII] 88 $\mu$m line and the underlying dust continuum in the two quasars in the reionization epoch, J205406.48-000514.8 (hereafter J2054-0005) at $z=6.0391\pm 0.0002$ and J231038.88+185519.7 (hereafter J2310+1855) at $z=6.0035\pm 0.0007$. The [OIII] luminosity of J2054-0005 and J2310+1855 are $L_{\rm [OIII]} = (6.8\pm0.6) \times 10^{9}$and$(2.4\pm0.6) \times 10^{9}$ $L_{\odot }$, corresponding to $\approx$ 0.05%\ and 0.01%\ of the total infrared luminosity, $L_{\rm TIR}$,respectively\mathrm{.}Combiningthese[OIII]luminositieswith[CII]158$\mu$m luminosities in the literature, we find that J2054-0005 and J2310+1855 have the [OIII]-to-[CII] luminosity ratio of $2.1\pm 0.4$ and $0.3\pm 0.1$, respectively, the latter of which is the lowest among objects so far reported at $z>6$. Combining [OIII] observations at $z\approx 6-9$ from our study and the literature, we identify the [OIII] line deficit: objects with larger $L_{\rm TIR}$havelower$L_{\rm [OIII]}$-to-$L_{\rm TIR}$ ratios. Furthermore, we also find that the anti-correlation is shifted toward higher $L_{\mathrm{T}\mathrm{I}\mathrm{R}}$ value when compared to the local [OIII] line deficit.