Massive galaxy formation caught in action at z ∼ 5 with JWST

Abstract

We report the discovery of a compact group of galaxies, CGG-z5, at z ∼ 5.2 in the EGS field covered by the JWST/CEERS survey. CGG-z5 was selected as the highest overdensity of galaxies at z > 2 in recent JWST public surveys and it consists of six candidate members lying within a projected area of 1.5 ′′ × 3 ′′ (10×20 kpc 2 ). All group members are HST/F435W and HST/F606W dropouts while securely detected in the JWST/NIRCam bands, yielding a narrow range of robust photometric redshifts 5.0 < z < 5.3. The most massive galaxy in the group has a stellar mass log(M * /M ⊙ ) ≈ 9.8, while the rest are low-mass satellites (log(M * /M ⊙ ) ≈ 8.4-9.2). While several group members were already detected in the HST and IRAC bands, the low stellar masses and the compactness of the structure required the sensitivity and resolution of JWST for its identification. To assess the nature and evolutionary path of CGG-z5, we searched for similar compact structures in the Eagle simulations and followed their evolution with time. We find that all the identified structures merge into a single galaxy by z = 3 and form a massive galaxy (log(M * /M ⊙ ) >11) at z ∼ 1. This implies that CGG-z5 could be a "proto-massive galaxy" captured during a short-lived phase of massive galaxy formation.

JADES: Resolving the Stellar Component and Filamentary Overdense Environment of Hubble Space Telescope (HST)-dark Submillimeter Galaxy HDF850.1 at z = 5.18

“…Five galaxies are spectroscopically confirmed at z = 5.220-5.222 within a separation of 2″ (∼12 proper kpc, hereafter pkpc), making it the most overdense region of z > 5 galaxies in the joint footprint of JADES and FRESCO in the GOODS-N field. Similar compact assemblies of z  5 galaxies have been reported in recent JWST/NIRCam studies (Helton et al 2023;Jin et al 2023), which are suggested as the progenitors of massive galaxies (stellar mass M star  10 11 M e ) seen at lower redshifts. The two galaxies to the northwest of the bright central galaxy are blended in ground-based images obtained with the SHARDS survey (SHARDS20013448; Pérez- González et al 2013;Arrabal Haro et al 2018), which were later spectroscopically confirmed at z = 5.224 through the detection of Lyα emission (Calvi et al 2021).…”

JWST Insight into a Lensed HST-dark Galaxy and Its Quiescent Companion at z = 2.58

“…We extract the sources by using a detection image combined from all noise weighted "wide" (W) NIRCam Long Wavelength (LW) filters available, this includes F277W, F356W, and F444W. A similar detection method for JWST data was employed in Jin et al (2023). For source extraction and the segmentation map, we used SEP (Barbary 2016), a PYTHON version of SEXTRACTOR (Bertin & Arnouts 1996).…”

“…At higher redshift, galaxies are less massive and more compact given the mass-size relation (e.g., see van der Wel et al 2014). Therefore, we scale the intrinsic SED accounting for multiple effects: (1) surface brightness dimming with (1 + z) 4 ; (2) using the merger trees in Jin et al (2023), we assumed that the galaxy has log (M * /M e ) = 10.8 at z = 4 and log (M * /M e ) = 10 at z = 6; (3) adopting the stellar mass-size relation at different redshift from Costantin et al (2022) for simulated 3 < z < 6 galaxies in JWST F356W image, i.e., r eff ∝ (1 + z) −0.14 ; (4) accounting for the physical scale to angular scale scaling at the assumed redshift. In order to consistently compare to the depths of JWST surveys.…”

A Massive Quiescent Galaxy in a Group Environment at z = 4.53

“…Our work suggests this core-scale quenching has already occurred at z > 4 by gas consumption due to the starburst and/or AGN feedback. Furthermore, recent JWST observations confirm compact galaxy groups at 5 < z < 8 (e.g., Hashimoto et al 2023;Helton et al 2024;Jin et al 2023;Morishita et al 2023;Sun et al 2024). Member galaxies are mostly low-mass SFGs, but Helton et al (2024) show that more massive galaxies with larger SFR populate the overdensity region compared to the field.…”