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Journal Club
JWST, ALMA, and Keck Spectroscopic Constraints on the UV Luminosity Functions at z~7-14: Clumpiness and Compactness of the Brightest Galaxies in the Early Universe
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Europe/Rome
Aula Rosino (Dipartimento di Fisica e Astronomia - Edificio ex-Rizzato)
Aula Rosino
Dipartimento di Fisica e Astronomia - Edificio ex-Rizzato
Description
Speakers: Michele Catone (Università degli Studi di Padova)
We present a JWST and Atacama Large Millimeter/submillimeter Array (ALMA) detailed study of the interstellar medium properties of high-redshift galaxies. Our JWST/NIRSpec integral field unit spectroscopy targeting three galaxies at z = 6─7 detects key rest-frame optical emission lines, allowing us to derive [O II] λλ3726, 3729─based electron densities of ne,optical ∼ 1000 cm−3 on average and [O III] λ4363─based metallicities of 12+log(O/H)=8.0-8.2 in two galaxies. New ALMA Band 9 and 10 observations detect the [O III] 52 μm line in one galaxy but do not in the others, resulting in far-infrared (FIR)-based densities of ne,FIR ≲ 500 cm−3 from the [O III] 52 μm/[O III] 88 μm ratio, systematically lower than the optical [O II]-based measurements. These low FIR-based densities are comparable to those at both z ∼ 0 and z > 6 in the literature, including JADES-GS-z14-0 at z = 14.18, suggesting little evolution up to z ∼ 14, in contrast to the increasing trend of optical-based densities with redshift. By conducting a JWST and ALMA joint analysis using emission lines detected with both telescopes, we find that the observed FIR [O III] 52 and 88 μm luminosities are too high to be explained by the optical-based densities at which they would be significantly collisionally de-excited. Instead, a two-zone model with distinct high- and low-density regions is required to reproduce all observed lines, indicating that FIR [O III] emission arises predominantly from low-density gas, while the optical [O III] and [O II] lines trace both regions. We further demonstrate that the direct-Te method can sometimes significantly underestimate metallicities up to 0.8 dex due to the presence of the low-density gas not fully traced by optical lines alone, highlighting the importance of combining optical and FIR lines to accurately determine gas-phase metallicities in the early Universe.