Stacking PANCAKEZ: sPectroscopic Analysis with NirspeC stAcKs in the Epoch of reioniZation. Weak ISM Absorption and Implications for Ionizing Photon Escape at $z\sim7$

Understand

We present a spectral stacking analysis of galaxies at $z\geq6$ observed with the James Webb Space Telescope (JWST).

• We curate a sample of $64$ galaxies spanning redshifts $z_{\rm spec} = 6.0 - 9.4$ which have NIRSpec medium resolution data.
• The stacks achieve sufficient signal-to-noise to measure equivalent widths (EW) and velocity centroids ($v_{\rm{cen}}$) of low-ionization species (LIS) absorption features, transmitted Lyman-alpha ($\rm{Ly\alpha}$) emission, and nebular emission lines.
• Overall, we find our sample has weaker LIS absorption lines ($\rm{EW}(\rm{LIS}) \approx 1 \r{A}$), smaller $v_{\rm{cen,LIS}} \approx -20 \pm 50~ \rm{km} \; \rm{s}^{-1}$, and significantly suppressed $\rm{Ly\alpha}$ emission ($\rm{EW}(\rm{Ly\alpha}) \approx 5~\r{A}$), compared to similar studies undertaken at lower redshift.