# JWST reveals a possible $z \sim 11$ galaxy merger in triply-lensed MACS0647$-$JD

**Authors:** Tiger Yu-Yang Hsiao, Dan Coe,  Abdurrouf, Lily Whitler, Intae Jung, Gourav Khullar, Ashish Kumar Meena, Pratika Dayal, Kirk S. S. Barrow, Lillian Santos-Olmsted, Adam Casselman, Eros Vanzella, Mario Nonino, Yolanda Jimenez-Teja, Masamune Oguri, Daniel P. Stark, Lukas J. Furtak, Adi Zitrin, Angela Adamo, Gabriel Brammer  
**arXiv:** [2210.14123](https://arxiv.org/abs/2210.14123)  
**Date:** 2022-10-25  
**Summary page:** https://www.summarizepaper.com/en/paper/2210.14123v1/

## Key points

- MACS0647$-$JD is a galaxy discovered at a redshift of approximately 11 with the Hubble Space Telescope.
- Recent observations using the James Webb Space Telescope (JWST) reveal that it consists of two components, possibly merging galaxies or stellar complexes within a single galaxy.
- Component A is larger and brighter, with an intrinsically blue color indicating recent star formation activity without significant dust obscuration. It has an effective radius of approximately 70 parsecs.
- Component B is smaller and appears redder in color, suggesting an older age and mild dust extinction. It has a smaller radius of about 20 parsecs.
- Simulations suggest that components A and B may be undergoing a galaxy merger occurring approximately 400 million years after the Big Bang.
- Another companion galaxy labeled as C located nearby is likely to merge with A and B in the future.
- The combined light from components A and B is magnified by factors of approximately 8, 5, and 2 in three lensed images named JD1, JD2, and JD3 respectively.
- MACS0647$-$JD stands out as significantly brighter than other galaxies recently discovered at similar redshifts using JWST.
- Its photometric redshift estimate is $z=10.6\pm0.3$, based on measurements in six NIRCam filters spanning a wavelength range from $1-5\mu m$.
- Further observations using the JWST NIRSpec instrument planned for January 2023 will provide a spectroscopic redshift measurement and enable more detailed study into its physical properties.

## Summary

MACS0647$-$JD is a remarkable galaxy discovered at a redshift of approximately 11 with the Hubble Space Telescope. Recent imaging observations using the James Webb Space Telescope (JWST) have provided new insights into this galaxy, revealing that it consists of two components that could either be merging galaxies or stellar complexes within a single galaxy. Both components are relatively small, with stellar masses around $10^8$ solar masses and radii less than 100 parsecs. The larger and brighter component, referred to as "A," exhibits an intrinsically blue color, suggesting recent star formation activity without significant dust obscuration. It has an effective radius of approximately 70 parsecs. On the other hand, the smaller component, labeled as "B," appears redder in color, indicating an older age (around 100-200 million years) and mild dust extinction (with an estimated visual extinction of approximately 0.1 magnitudes). Component B has a smaller radius of about 20 parsecs. Interestingly, simulations of high-redshift galaxies with similar colors reveal that their star formation histories are out of phase; this suggests that we may be witnessing a galaxy merger between components A and B occurring approximately 400 million years after the Big Bang. Furthermore, another companion galaxy labeled as C located about 3 kiloparsecs away from A and B is likely destined to merge with them in the future. The combined light from components A and B is magnified by factors of approximately 8, 5 and 2 in three lensed images named JD1, JD2 and JD3 respectively; their fluxes measured in F356W filter correspond to approximately 322 nJy (AB magnitude of 25.1), 203 nJy (AB magnitude of 25.6) and 86 nJy (AB magnitude of 26.6). MACS0647$-$JD stands out as significantly brighter than other galaxies recently discovered at similar redshifts using JWST; without the gravitational lensing magnification its apparent magnitude would be around 27.3 (corresponding to an absolute magnitude of $M_{UV}=-20.4$). Based on photometry measurements in six NIRCam filters spanning a wavelength range from $1-5\mu m$, a photometric redshift estimate of $z=10.6\pm0.3$ has been obtained for MACS0647$-$JD with a high confidence level; however further observations using the JWST NIRSpec instrument planned for January 2023 will provide a spectroscopic redshift measurement and enable more detailed study into its physical properties..