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Arxiv: Between the Extremes: A JWST Spectroscopic Benchmark for High Redshift Galaxies Using ~500 Confirmed Sources at z\geqslant5 Published: 3/11/2024 8:57:00 PM Updated: 3/11/2024 8:57:00 PM

Paper abstract: The exceptional spectra of the most luminous z>10 sources observed so farhave challenged our understanding of early galaxy evolution, requiring a newobservational benchmark for meaningful interpretation. As such, we constructspectroscopic templates representative of high-redshift, star-formingpopulations, using 482 confirmed sources at z=5.0-12.9 with JWST/NIRSpecprism observations, and report on their average properties. We find z=5-11galaxies are dominated by blue UV continuum slopes (\beta=-2.3 to -2.7) andinverse Balmer jumps, characteristic of dust-poor and young systems, with ashift towards bluer slopes and younger ages with redshift. The evolution ismirrored by ubiquitous CIII] detections across all redshifts (EW_{0}=5-14\r{A}), which increase in strength towards early times. Rest-frame opticallines reveal elevated ratios (O32=7-31, R23=5-8, and Ne3O2=1-2) andsubsolar metallicities (log O/H=7.3-7.9), typical of ionization conditionsand metallicities rarely observed in z~0 populations. Within our sample,we identify 57 Ly\alpha-emitters which we stack and compare to a matchedsample of non-emitters. The former are characterized by more extreme ionizingconditions with enhanced CIII], CIV, and HeII+[OIII] line emission, youngerstellar populations from inverse Balmer jumps, and a more pristine ISM seenthrough bluer UV slopes and elevated rest-frame optical line ratios. The novelcomparison illustrates important intrinsic differences between the twopopulations, with implications for Ly\alpha visibility. The spectraltemplates derived here represent a new observational benchmark with which tointerpret high-redshift sources, lifting our constraints on their globalproperties to unprecedented heights and extending out to the earliest of cosmictimes.