A Nitrogen-rich AGN Powering a Large Ionizing Bubble at z=8.63

Abstract

We report the detection of Ly${\alpha}$ in CANUCS-LRD-z8.6, a recently discovered AGN at z = 8.63 by Tripodi et al. (2024), in new NIRSpec/MSA G140H/F070LP observations. We detect broad Ly${\alpha}$ emission (FWHM $= 1540 \pm 260$ km/s) near the systemic velocity, which suggests a large ionizing bubble considering that the universe is almost fully neutral at the redshift. Through Ly${\alpha}$ line-shape modeling assuming a Stromgren sphere, we find a large bubble radius, $R_b = 1.5^{+0.3}_{-0.2}$ pMpc, and a moderately high Ly${\alpha}$ escape fraction, $f_{esc} = 11 \pm 3$ %. The intrinsic line width is inferred to be broad ($2200 \pm 280$ km/s), likely originating in the broad-line region. Existing data indicate that CANUCS-LRD-z8.6 is within a mild overdensity, $\delta = 1.8^{+3.0}_{-0.6}$, suggesting that other galaxies in its proximity might have contributed to the formation of the bubble. The high N IV]${\lambda}$1488 / C IV${\lambda}$1548 and N IV]${\lambda}$1488 / O III]${\lambda}$1661 line ratios measured in existing NIRSpec/PRISM data indicate nitrogen enrichment in this metal-poor, low-luminosity AGN. The spectroscopic features are overall similar to other nitrogen-rich galaxies discovered in the literature, such as GN-z11 and GHZ2/GLASSz12. This suggests that CANUCS-LRD-z8.6 may represent one of the evolutionary phases of those nitrogen-rich galaxies.