SPURS: Massive Stars, Dense Gas, and Ly$\alpha$ Escape in GN-z11 at $z=10.6$

Abstract

We present ultra-deep {\it JWST} spectroscopy of GN-z11 ($z=10.6$) obtained through the SPURS Cycle 4 Large Program, providing the deepest rest-UV view yet obtained of a galaxy at $z>10$. GN-z11 was previously found to be nitrogen-enhanced with detectable Ly$\alpha$. The SPURS spectrum reveals P-Cygni stellar wind features and broad He II emission that are jointly reproduced by stellar population models incorporating very massive stars (VMS; $>100M_{\odot }$) at low metallicity and young ages ($\lesssim 3$ Myr). We also detect a broad ($\mathrm{FWHM}=1670$ km s${}^{-1}$) component to N IV] $\lambda 1486$, now seen in several nitrogen emitters, potentially arising from dense WN-like winds or LBV-like outbursts associated with a population of VMS in a dense environment, though an AGN-driven wind cannot be excluded. In either scenario, this broad component may trace the gas producing GN-z11's nitrogen enhancement. Rest-UV absorption lines reveal a fast ($\sim 500$~km~s${}^{-1}$), highly ionized outflow and a negligible neutral gas covering fraction. We resolve the weak Ly$\alpha$ emission (EW=5.6 Å, $f_{\mathrm{esc},\mathrm{Ly}\alpha }=2.7$\%), finding a broad red wing (44\% of flux at $>500$ km s${}^{-1}$) that should experience reduced IGM damping wing suppression and help explain Ly$\alpha$ visibility at $z>10$. Fine-structure O I* $\lambda 1304$ emission indicates dense neutral gas near a subset of the ionizing sources, which may also scatter Ly$\alpha$ to the large observed velocities. The weak low-ionization absorption favors a picture in which this dense neutral gas is confined to a compact nuclear region. Together, these results are consistent with a rapid burst of star formation building up the dense nuclear regions and surrounding clusters in GN-z11.

46 pages, 25 figures. Submitted to ApJ