A Nitrogen-rich AGN Powering a Large Ionizing Bubble at <i>z</i> = 8.63

Abstract We report the detection of Ly α in CANUCS-LRD-z8.6, a recently discovered active galactic nucleus (AGN) at z = 8.63 by R. Tripodi et al. (2025), in new NIRSpec/MSA G140H/F070LP observations. We detect broad Ly α emission (FWHM = 1540 ± 260 km s −1 ) near the systemic velocity, which suggests a large ionizing bubble, considering that the Universe is almost fully neutral at the redshift. Through Ly α line-shape modeling assuming a Strömgren sphere, we find a large bubble radius, R b = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> pMpc, and a moderately high Ly α escape fraction, f esc = 11% ± 3%. The intrinsic line width is inferred to be broad (2200 ± 280 km s −1 ), likely originating in the broad-line region. Existing data indicate that CANUCS-LRD-z8.6 is within a mild overdensity, δ = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3.0</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , suggesting that other galaxies in its proximity might have contributed to the formation of the bubble. The high N IV ] λ 1488 /C IV λ 1548 and N IV ] λ 1488 /O III ] λ 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 those of 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.