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, $R_b=1.5_{-0.2}^{+0.3}$ 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, $\delta =1.8_{-0.6}^{+3.0}$, 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.

accepted for publication in ApJ