The JWST EXCELS survey: an extremely metal-poor galaxy at $z=8.271$ hosting an unusual population of massive stars
F. Cullen, A. C. Carnall, D. Scholte, D. J. McLeod, R. J. McLure, K. Z. Arellano-C\'ordova, T. M Stanton, C. T. Donnan, J. S. Dunlop, A. E. Shapley, L. Barrufet, R. Begley, C. Bondestam, M. Cirasuolo, H.-H. Leung, C. L. Pollock, S. Stevenson

TL;DR
This paper reports the discovery of an extremely metal-poor galaxy at redshift 8.271 with unusual stellar populations, analyzed through JWST spectroscopy, revealing insights into early galaxy formation and stellar initial mass functions.
Contribution
It provides the first detailed spectroscopic analysis of a very low-metallicity galaxy at high redshift, suggesting a possible top-heavy IMF or exotic stellar populations.
Findings
Oxygen abundance is among the lowest measured in any galaxy.
The galaxy hosts an ionizing source with very high effective temperature.
Standard stellar population models cannot explain the observed heating.
Abstract
We present an analysis of the rest-frame optical (\r{A}) spectrum of a star-forming galaxy at from JWST/NIRSpec medium-resolution observations taken as part of the EXCELS survey. The galaxy (EXCELS-63107) is compact, with a size consistent with the size of local star-forming cluster complexes () and has an extremely steep UV continuum measured from JWST/NIRCam photometry (). The JWST/NIRSpec G395M spectrum of EXCELS-63107 is notable for its strong [OIII] auroral-line emission relative to the [OIII] forbidden line. Via a detailed emission-line and photoionization-modelling analysis, we find that the the observed properties of EXCELS-63107 are consistent with the presence of an ionizing source with an effective temperature of $T_{\rm eff}…
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Taxonomy
TopicsAstronomy and Astrophysical Research · Galaxies: Formation, Evolution, Phenomena · Stellar, planetary, and galactic studies
