Evidence of Extreme Ionization Conditions and Low Metallicity in GHZ2/GLASS-Z12 from a Combined Analysis of NIRSpec and MIRI Observations
Journal article, 2024

GHZ2/GLASS-z12, one of the most distant galaxies found in JWST observations, has been recently observed with both the NIRSpec and MIRI spectrographs, establishing a spectroscopic redshift zspec = 12.34 and making it the first system at z > 10 with complete spectroscopic coverage from rest-frame UV to optical wavelengths. This galaxy is identified as a strong C IVλ1549 emitter (EW = 46 Å) with many other detected emission lines, such as N IV]λ1488, He IIλ1640, OIII]λλ1661,1666, NIII]λ1750, C III]λλ1907,1909, [O II]λλ3726,3729, [Ne III]λ3869, [O III]λλ4959,5007, and Hα, including a remarkable detection of the O III Bowen fluorescence line at rest frame λ = 3133 Å. We analyze in this paper the joint NIRSpec + MIRI spectral data set. Combining six optical strong-line diagnostics (namely R2, R3, R23, O32, Ne3O2, and Ne3O2Hd), we find extreme-ionization conditions, with log10 ([O III]λλ4959,5007/[O II]λλ3726,3729) = 1.39 ± 0.19 and log10 ([Ne III]λ3869/[O II]λλ3726,3729) = 0.37 ± 0.18 in stark excess compared to typical values in the interstellar medium (ISM) at lower redshifts. These line properties are compatible either with an active galactic nucleus (AGN) or with a compact, very dense star-forming environment (ΣSFR ; 102-103Me yr-1 kpc-2 and*SM ; 104-105Me pc-2), with a high ionization parameter (log10(U) = -1.75 ± 0.16), a high ionizing photon production efficiency (x ) = - log 25.7+ ion 0.1 0.3, and a low gas-phase metallicity (also confirmed by the direct, Te method) ranging between 4% and 11% Ze, indicating a rapid chemical enrichment of the ISM in the past few megayears. These properties also suggest that a substantial amount of ionizing photons (∼10%) are leaking outside of GHZ2 and starting to reionize the surrounding intergalactic medium, possibly due to strong radiation-driven winds. The general lessons learned from GHZ2 are the following: (i) the UV-to-optical combined nebular indicators are broadly in agreement with UV-only or optical-only indicators; (ii) UV+optical diagnostics fail to discriminate between an AGN and star formation in a low-metallicity, high-density, and extreme-ionization environment; and (iii) comparing the nebular line ratios with local analogs may be approaching its limits at z ≳10, as this approach is potentially challenged by the unique conditions of star formation experienced by galaxies at these extreme redshifts.

Lyman-break galaxies (979)

Early universe (435)

Primordial galaxies (1293)

High-redshift galaxies (734)

Author

Antonello Calabrò

Osservatorio Astronomico di Roma

M. Castellano

Osservatorio Astronomico di Roma

J. A. Zavala

National Astronomical Observatory of Japan

L. Pentericci

Osservatorio Astronomico di Roma

Pablo Arrabal Haro

NOIRLab

Tom Bakx

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

Denis Burgarella

Laboratoire d'Astrophysique de Marseille

Caitlin M. Casey

The University of Texas at Austin

Mark Dickinson

NOIRLab

Steven L. Finkelstein

The University of Texas at Austin

A. Fontana

Osservatorio Astronomico di Roma

Mario Llerena

Osservatorio Astronomico di Roma

Sara Mascia

Osservatorio Astronomico di Roma

E. Merlin

Osservatorio Astronomico di Roma

Ikki Mitsuhashi

National Astronomical Observatory of Japan

University of Tokyo

Lorenzo Napolitano

Sapienza University of Rome

Osservatorio Astronomico di Roma

Diego Paris

Osservatorio Astronomico di Roma

P.G.P. Pérez-González

Centro de Astrobiologia (CAB)

Guido Roberts-Borsani

University of California

P. Santini

Osservatorio Astronomico di Roma

Tommaso Treu

University of California

Eros Vanzella

Istituto nazionale di astrofisica (INAF)

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 975 2 245

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.3847/1538-4357/ad7602

More information

Latest update

11/25/2024