Detections of [OIII] 88 $\hat{I}¼$m in Two Quasars in the Reionization Epoch

Abstract

With the Atacama Large Millimeter/sub-millimeter Array (ALMA), we report detections of the far-infrared (FIR) [OIII] 88 $\hat{I}¼$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 $L_{[\mathrm{OIII}]}=(6.8\pm 0.6)\times 10^9$ and $(2.4\pm 0.6)\times 10^9$ $L_{\odot }$, corresponding to $\approx$ 0.05\%\ and 0.01\%\ of the total infrared luminosity, $L_{\mathrm{TIR}}$, respectively. Combining these [OIII] luminosities with [CII] 158 $\hat{I}¼$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 $L_{\mathrm{TIR}}$ have lower $L_{[\mathrm{OIII}]}$-to-$L_{\mathrm{TIR}}$ ratios. Furthermore, we also find that the anti-correlation is shifted toward higher $L_{\mathrm{TIR}}$ value when compared to the local [OIII] line deficit.

10 pages, 3 figures, 1 table, accepted for publication in PASJ