First look with JWST spectroscopy: $z 8$ galaxies resemble local
analogues
(2022)cite arxiv:2207.10034Comment: 5 pages, 5 Figures. Submitted to Astronomy & Astrophysics Letters.Abstract
Deep images and near-IR spectra of galaxies in the field of the lensing
cluster SMACS J0723-37327 were recently taken in the Early Release Observations
program of JWST. Among these, two NIRSpec spectra of galaxies at $z=7.7$ and
one at $z=8.5$ were obtained, revealing for the first time rest-frame optical
emission line spectra of galaxies in the epoch of reionization, including the
detection of the important OIII4363 auroral line (see JWST PR 2022-035). We
present an analysis of the emission line properties of these galaxies, finding
that these galaxies have a high excitation (as indicated by high ratios of
OIII/OII, NeIII/OII), strong OIII4363/H$\gamma$, high equivalent
widths, and other properties which are typical of low-metallicity star-forming
galaxies. Using the direct method we determine oxygen abundances of
$12+łog(O/H)=7.85$ in two $z=7.7$ galaxies, and a lower metallicity of
$12+łog(O/H)7.36-7.50$ in the $z=8.5$ galaxy using different strong
line methods. With stellar masses estimated from SED fits, we find that the
three galaxies lie close to or below the $z 2$ mass-metallicity relation.
Overall, these first galaxy spectra at $z 8$ show a strong resemblance of
the emission lines properties of galaxies in the epoch of reionization with
those of relatively rare local analogues previously studied from the SDSS.
Clearly, these first JWST observations demonstrate already the incredible power
of spectroscopy to reveal properties of galaxies in the early Universe.
Description
First look with JWST spectroscopy: $z \sim 8$ galaxies resemble local analogues