TY - JOUR

T1 - First look with JWST spectroscopy

T2 - Resemblance among z similar to 8 galaxies and local analogs

AU - Schaerer, D.

AU - Marques-Chaves, R.

AU - Barrufet, L.

AU - Oesch, P.

AU - Izotov, Y. I.

AU - Naidu, R.

AU - Guseva, N. G.

AU - Brammer, G.

PY - 2022/9/16

Y1 - 2022/9/16

N2 - Deep images and near-IR spectra of galaxies in the field of the lensing cluster SMACS J0723.3-7327 were recently taken as part of the Early Release Observations (EROs) program of the James Webb Space Telescope (JWST). Among these, two NIRSpec spectra of galaxies, at z = 7.7 and at z = 8.5, were obtained, revealing, for the first time, the rest-frame optical emission line spectra of galaxies in the epoch of reionization, including the detection of the important [O III]lambda 4363 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 [O III]lambda 5007/[O II] lambda 3727, [Ne III] lambda 3869/[O II] lambda 3727), strong [O III]lambda 4363, high equivalent widths, and other properties typical of low-metallicity star-forming galaxies. Using the direct method, we determined oxygen abundances of 12 + log(O/H)approximate to 7.9 in two z = 7.7 galaxies and a lower metallicity of 12 + log(O/H)approximate to 7.4 - 7.5 (similar to 5% solar) in the z = 8.5 galaxy using different strong line methods. More accurate metallicity determinations will require better data. With stellar masses estimated from spectral energy distribution (SED) fits, we find that the three galaxies lie close to or below the z similar to 2 mass-metallicity relation. Overall, these first galaxy spectra at z similar to 8 show a strong resemblance in their the emission line properties of galaxies in the epoch of reionization with those of relatively rare local analogs previously studied with the SDSS. Clearly, the first JWST observations demonstrate already the incredible power of spectroscopy to reveal the properties of galaxies in the early Universe.

AB - Deep images and near-IR spectra of galaxies in the field of the lensing cluster SMACS J0723.3-7327 were recently taken as part of the Early Release Observations (EROs) program of the James Webb Space Telescope (JWST). Among these, two NIRSpec spectra of galaxies, at z = 7.7 and at z = 8.5, were obtained, revealing, for the first time, the rest-frame optical emission line spectra of galaxies in the epoch of reionization, including the detection of the important [O III]lambda 4363 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 [O III]lambda 5007/[O II] lambda 3727, [Ne III] lambda 3869/[O II] lambda 3727), strong [O III]lambda 4363, high equivalent widths, and other properties typical of low-metallicity star-forming galaxies. Using the direct method, we determined oxygen abundances of 12 + log(O/H)approximate to 7.9 in two z = 7.7 galaxies and a lower metallicity of 12 + log(O/H)approximate to 7.4 - 7.5 (similar to 5% solar) in the z = 8.5 galaxy using different strong line methods. More accurate metallicity determinations will require better data. With stellar masses estimated from spectral energy distribution (SED) fits, we find that the three galaxies lie close to or below the z similar to 2 mass-metallicity relation. Overall, these first galaxy spectra at z similar to 8 show a strong resemblance in their the emission line properties of galaxies in the epoch of reionization with those of relatively rare local analogs previously studied with the SDSS. Clearly, the first JWST observations demonstrate already the incredible power of spectroscopy to reveal the properties of galaxies in the early Universe.

KW - galaxies: high-redshift

KW - dark ages, reionization, first stars

KW - galaxies: ISM

KW - EMISSION-LINE GALAXIES

KW - STAR-FORMING GALAXIES

KW - O III EMITTERS

KW - PHOTON PRODUCTION

KW - EVOLUTION

KW - SDSS

KW - I.

U2 - 10.1051/0004-6361/202244556

DO - 10.1051/0004-6361/202244556

M3 - Journal article

VL - 665

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

M1 - L4

ER -