# Hidden giants in JWST's PEARLS: An ultra-massive z=4.26 sub-millimeter galaxy that is invisible to HST

**Authors:** Ian Smail, Ugne Dudzeviciute, Mark Gurwell, Giovanni G. Fazio, S. P. Willner, A. M. Swinbank, Vinodiran Arumugam, Jake Summers, Seth H. Cohen, Rolf A. Jansen, Rogier A. Windhorst, Ashish Meena, Adi Zitrin, William C. Keel, Dan Coe, Christopher J. Conselice, Jordan C. J. D'Silva, Simon P. Driver, Brenda Frye, Norman A. Grogin  
**arXiv:** [2306.16039](https://arxiv.org/abs/2306.16039)  
**Date:** 2023-06-28  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.16039v1/

## Key points

- Study focuses on two strongly star-forming galaxies, 850.1 and 850.2, at redshift z=4.26
- Various telescopes used for analysis: SMA, JCMT, NOEMA, JWST, HST, SST
- Both galaxies exhibit bright dust continuum emission at submillimeter wavelengths
- 850.2 detected in UV as a Lyman-break galaxy, while 850.1 remains undetected at wavelengths shorter than 2um
- Pixel-level spectral energy distribution (SED) analysis used to derive maps of stellar mass and visual extinction (Av)
- 850.1 is one of the most massive and highly obscured galaxies known at z>4 with Av ~5 and stellar mass ~10^11.8 Mo
- Galaxy formation for 850.1 likely occurred at redshifts greater than 6
- 850.2 is one of the least massive and least obscured members of dusty star-forming population at z>4 with Av ~1
- Diversity between the two galaxies highlights incompleteness of surveys conducted solely on imaging <2um when studying high redshift galaxies comprehensively
- Resolved mass map shows compact stellar mass distribution for galaxy 850.1 with effective radius Re ~1 kpc
- Galaxy expected to evolve into a massive quiescent system due to merging events with its satellite companion galaxy 850.2
- Stellar morphology exhibits arms and linear bar feature attributed to active dynamical processes within group environment

## Summary

In this study, the authors present a multi-wavelength analysis of two strongly star-forming galaxies, 850.1 and 850.2, located at redshift z=4.26 and observed through the massive cluster lens A1489. The authors utilize data from various telescopes including SMA, JCMT, NOEMA, JWST, HST, and SST to investigate the stellar, ISM (interstellar medium), and dynamical properties of these galaxies. Both 850.1 and 850.2 exhibit bright dust continuum emission at submillimeter wavelengths. However, while 850.2 is also detected in the UV as a Lyman-break galaxy, 850.1 remains undetected at wavelengths shorter than 2 micrometers (um), even with deep JWST/NIRCam observations. The authors perform a pixel-level spectral energy distribution (SED) analysis to derive sub-kiloparsec-resolution maps of stellar mass and visual extinction (Av). They find that 850.1 is one of the most massive and highly obscured galaxies known at redshifts greater than 4 (z>4), with an Av value of approximately 5 and a stellar mass of around 10^11.8 times the mass of the Sun (Mo). This suggests that galaxy formation for 850.1 likely occurred at redshifts greater than 6. On the other hand, 850.2 is one of the least massive and least obscured members of the dusty star-forming population at z>4, with an Av value of approximately 1. The diversity exhibited by these two dust-mass-selected galaxies highlights the incompleteness of galaxy surveys conducted solely on imaging at wavelengths shorter than 2um – which are typically feasible using instruments such as HST or ground-based telescopes – when attempting to understand high redshift galaxies in their entirety. The resolved mass map of galaxy 850.1 reveals a compact stellar mass distribution with an effective radius (Re) of approximately 1 kiloparsec (kpc). The expected evolution of this galaxy to lower redshifts aligns with properties observed in massive quiescent galaxies at z~1.5 and ultra-massive early type galaxies at z~0; suggesting that it will eventually become one such system in its future evolution cycle due to merging events with its satellite companion galaxy 850.2 which has been identified as part of its group environment by this study's authors based on its proximity to galaxy 850 . Additionally ,the stellar morphology exhibits arms and a linear bar feature which can be attributed to active dynamical processes occurring within this group environment . Overall ,this study provides valuable insights into high redshift strongly star forming galaxies ,emphasizing how multi wavelength observations are necessary for obtaining comprehensive understanding about them .