James Webb Space Telescope Feed Post

Harvard ADS: Low [O/Fe] Ratio in a Luminous Galaxy at the Early Cosmic Epoch (z>10): Signature of Short Delay Time or Bright Hypernovae/Pair-Instability Supernovae?

Paper abstract: We present an [O/Fe] ratio of a luminous galaxy GN-z11 at z=10.60 derived with the deep public JWST/NIRSpec data. We fit the medium-resolution grating data with the model spectra consisting of BPASS-stellar and CLOUDY-nebular spectra in the rest-frame UV wavelength ranges with Fe absorption lines, carefully masking out the other emission and absorption lines in the same manner as previous studies conducted for lower redshift (z~ 2-6) galaxies with oxygen abundance measurements. We obtain an Fe-rich abundance ratio \mathrm{[O/Fe]}=-0.39^{+0.59}_{-0.36} that is confirmed with the independent deep prism data as well as by the classic 1978 index method. This [O/Fe] measurement is lower than that at z~ 2-3 and comparable with those at z~ 6. Because z=10.60 is an early epoch after the Big Bang (~ 430 Myr) and the first star formation (likely ~ 200 Myr), there is a difficulty in efficiently producing Fe by Type Ia supernovae (SNeIa) requiring sufficient delay time for white-dwarf formation and gas accretion. The Fe-rich abundance ratio in GN-z11 suggests that the delay time is short, or that the major Fe enrichment is not accomplished by SNeIa but bright hypernovae (BrHNe) and/or pair-instability supernovae (PISNe), where the yield models of BrHNe and PISNe explain Fe, Ne, and O abundance ratios of GN-z11. The [O/Fe] measurement is not too low to rule out the connection between GN-z11 and globular clusters (GCs) previously suggested by the nitrogen abundance, but rather confirms the connection with a GC population at high [N/O] if a metal dilution process exists.