A first look at the SMACS0723 JWST ERO: spectroscopic redshifts, stellar masses, and star-formation histories

Abstract

We present a first-look analysis of the JWST ERO data in the SMACS J0723.3-7327 cluster field. We begin by reporting 10 new spectroscopic redshifts from λobs = 1.8 − 5.2μm NIRSpec medium-resolution (R = λ/Δλ = 1000) data. These are determined via multiple high-SNR emission line detections, with 5 objects at 1 < z < 3 displaying multiple rest-frame near-infrared Hydrogen Paschen lines, and 5 objects at 5 < z < 9 displaying rest-frame optical Oxygen and Hydrogen Balmer lines. For the 5 higher-redshift galaxies we extract fluxes in 6 NIRCam bands spanning λobs = 0.8 − 5μm and perform spectral energy distribution fitting, in combination with existing HST photometry. The 7 < z < 9 objects exhibit a U-shaped pattern across the F277W, F356W and F444W bands, indicating a Balmer break seen in emission (Balmer jump) and high-equivalent-width [O iii] emission. This indicates an extremely young stellar population, with the bulk of the current mass having formed within the past 10 Myr. We report robust stellar masses and mean stellar ages from our spectral fitting, with the four z > 6 galaxies exhibiting low stellar masses from log10(M*/M⊙) = 7.1 − 8.2 and correspondingly young mean stellar ages of only a few Myr. This work highlights the critical importance of combining large upcoming NIRCam surveys with NIRSpec follow-up to measure the spectroscopic redshifts necessary to robustly constrain physical parameters.

JWST Sneaks a Peek at the Stellar Morphology of z ∼ 2 Submillimeter Galaxies: Bulge Formation at Cosmic Noon

“…However the much higher signal-to-noise ratio detection from the MIPS imaging suggests that the northern spiral galaxy is the counterpart. In addition, one recent JWST study has suggested that the southern compact source to be a z ∼ 4.5 quiescent galaxy (Carnall et al 2022). We therefore identify the northern spiral galaxy to be the JWST counterpart for 850.025.…”

Finding Peas in the Early Universe with JWST

“…The directly measured circularized half-light radii (i.e., corrected for the galaxy ellipticity) range from 0.28 to 0.42 kpc (see Table 3). If we apply a rough correction for lensing amplification due to the foreground galaxy cluster, using the reported magnification values from Carnall et al (2023) that were obtained from the lens model provided by the RELICS team (Coe et al 2019), the sizes drop to 0.1-0.26 kpc. These lensing corrections are modest for two of the sources, with the exception being a magnification ∼10 and a corresponding reduction in circularized radius of ∼1/3× for J072326-732656 (04590) (04590).…”

“…a Gravitational lensing magnifications are taken fromCarnall et al (2023). b Lensing corrected sizes are approximated as (observed radius)/ magnification .…”

A Comprehensive Study of Galaxies at z ∼ 9–16 Found in the Early JWST Data: Ultraviolet Luminosity Functions and Cosmic Star Formation History at the Pre-reionization Epoch

“…The infrared photometric properties of galaxies at z ∼ 1-2 are studied with the NIRCam and MIRI images of the ERO SMACS J0723 observations in conjunction with the ALMA archival data (Cheng et al 2022). The ERO NIRSpec observations in SMACS J0723 provide high-quality spectra that allow us to identify 10 galaxies at z = 1.2-8.5, 3 of which reside at z = 7.7-8.5 (Carnall et al 2023), and to characterize the interstellar medium of the galaxies (Schaerer et al 2022;Curti et al 2023). NIRISS spectroscopic data complements the NIRSpec observations and provide a spectroscopic sample of z ∼ 1-8 galaxies (Boyett et al 2022;Roberts-Borsani et al 2022;Wang et al 2022;Marchesini et al 2023).…”