A first systematic study of [OIII] 88$\hat{I}¼$m at $z>8$: two luminous oxygen lines and a powerful ionized outflow in the first 600 million years

Abstract

We present deep ALMA Band 7 observations of the [OIII] $88\hat{I}¼$m line and underlying dust continuum emission in four UV-bright, gravitationally lensed (magnification $\hat{I}¼=1.4-3.8$), JWST-selected galaxies at $z=8.5-10.3$, with observed magnitudes $-22.5\lesssim M_{\mathrm{UV}}\lesssim -20.5$. [OIII] $88\hat{I}¼$m is confidently detected in UNCOVER-10646 at $z=8.5080\pm 0.0011$ ($15\ddot{I}ƒ$) and DHZ1 at $z=9.3113\pm 0.0006$ ($6\ddot{I}ƒ$), with both being intrinsically luminous systems [$L_{\text{[OIII]}}=(1.1-1.6)\times 10^9{L}_{\odot }$] that follow the local [OIII]-SFR relation. [OIII] $88\hat{I}¼$m remains undetected in the two $z>10$ targets, including in the $z=10.07$ X-ray AGN UHZ1, where we obtain a deep limit of $L_{\text{[OIII]}}<6\times 10^7{L}_{\odot }$. Dust emission is not detected in any individual source nor in a stack ($<3\ddot{I}ƒ$). The high S/N [OIII] $88\hat{I}¼$m detection in UNCOVER-10646 uniquely reveals an additional broad component ($\mathrm{FWHM}=1366_{-329}^{+473}km/s$; $\hat{I}”\mathrm{BIC}\approx 20$) indicative of an ionized outflow. We infer a high outflow rate of ${\dot{M}}_{\mathrm{out}}=128_{-46}^{+80}{M}_{\odot }{\mathrm{yr}}^{-1}$, corresponding to a mass loading factor $\hat{I}\cdot ={\dot{M}}_{\mathrm{out}}/\mathrm{SFR}=2.9_{-1.0}^{+1.8}$ that matches or exceeds theoretical predictions and JWST-based studies of ionized outflows at high redshift. While high-resolution ALMA follow-up is required to confirm and spatially resolve the outflow, this first systematic study at $z>8$ highlights the unique diagnostic power of [OIII] $88\hat{I}¼$m in characterizing galaxies in the early Universe.

Published in the Open Journal of Astrophysics