# TEMPLATES: Characterization of a Merger in the Dusty Lensing SPT0418-47 System

**Authors:** Jared Cathey, Anthony H. Gonzalez, Sidney Lower, Kedar A. Phadke, Justin Spilker, Manuel Aravena, Jack E. Birkin, Simon Birrer, Scott Chapman, Håkon Dahle, Cristopher C. Hayward, Yashar Hezaveh, Ryley Hill, Taylor A. Hutchison, Guillaume Mahler, Daniel P. Marrone, Desika Narayanan, Alexander Navarre, Cassie Reuter, Jane R. Rigby  
**arXiv:** [2307.10115](https://arxiv.org/abs/2307.10115)  
**Date:** 2023-07-19  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.10115v1/

## Key points

- Study presents observations of lensing system SPT0418-47 using JWST and ALMA
- Lensing system consists of a strongly-lensed, dusty star-forming galaxy at z=4.225 and a multiply-imaged companion
- Observations confirm both galaxies are located at the same redshift
- Galaxies have a projected physical separation of $4.42\pm 0.05$ kiloparsecs
- Total magnifications derived: $\mu=29.5\pm1.2$ for SPT0418A and $\mu=4.2\pm 0.9$ for SPT0418B
- Stellar mass ratio approximately 4 to 1 ($4.5\pm 1.0$ for CIGALE and $4.2^{+1.9}_{-1.6}$ for PROSPECTOR)
- Extended structure observed suggesting possible tidal feature between the galaxies
- Despite interaction, star formation rates and stellar masses remain consistent with expectations

## Summary

In this study, the authors present the results of their observations of the lensing system SPT0418-47 using the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA). The lensing system consists of a strongly-lensed, dusty star-forming galaxy at a redshift of z=4.225, along with an associated multiply-imaged companion. The JWST NIRCam and MIRI imaging observations were obtained as part of the Early Release Science program called TEMPLATES (Targeting Extremely Magnified Panchromatic Lensed Arcs and Their Extended Star Formation). These observations provide robust and multiwavelength detection of stellar light in both the main galaxy (SPT0418A) and its companion (SPT0418B), confirming that they are located at the same redshift. From a source plane reconstruction, it is inferred that these two galaxies have a projected physical separation of $4.42\pm 0.05$ kiloparsecs. The authors derive total magnifications of $\mu=29.5\pm1.2$ for SPT0418A and $\mu=4.2\pm 0.9$ for SPT0418B using two different methods: CIGALE and PROSPECTOR. They also estimate the stellar masses of these galaxies; their ratio is approximately 4 to 1 ($4.5\pm 1.0$ for CIGALE and $4.2^{+1.9}_{-1.6}$ for PROSPECTOR). Additionally, extended structure associated with SPT0418A is observed in the lensing reconstruction which suggests a possible tidal feature between them; however, despite this interaction their star formation rates and stellar masses remain consistent with those expected from star-forming galaxies at this epoch indicating that it has not significantly impacted them yet.