# A Near-Infrared Faint, Far-Infrared-Luminous Dusty Galaxy at z~5 in COSMOS-Web

**Authors:** Jed McKinney, Sinclaire M. Manning, Olivia R. Cooper, Arianna S. Long, Hollis Akins, Caitlin M. Casey, Andreas L. Faisst, Maximilien Franco, Christopher C. Hayward, Erini Lambrides, Georgios Magdis, Katherine E. Whitaker, Min Yun, Jaclyn B. Champagne, Nicole E. Drakos, Fabrizio Gentile, Steven Gillman, Ghassem Gozaliasl, Olivier Ilbert, Shuowen Jin  
**arXiv:** [2304.07316](https://arxiv.org/abs/2304.07316)  
**Date:** 2023-04-14  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.07316v1/

## Key points

- A recent study has discovered a population of dusty, star-forming galaxies at high redshifts (z>4)
- These galaxies are invisible in deep extragalactic optical surveys but have been detected through far-infrared observations
- The researchers used the James Webb Space Telescope (JWST) to detect the rest-frame optical light of one such galaxy, AzTECC71
- AzTECC71 is among the reddest galaxies in COSMOS-Web and was previously undetected at wavelengths shorter than 850 microns
- It is undetected in near-infrared observations with NIRCam/F150W and F115W filters and appears fainter in the F444W filter compared to other sub-millimeter galaxies identified in COSMOS-Web
- There is a high probability (99%) that AzTECC71 is at a redshift greater than 4 (z>4), specifically with z_phot=5.7(+0.8,-0.7)
- AzTECC71 is found to be massive (logM*/Msun~10.7) and IR-luminous (logLIR/Lsun~12.7), comparable to other optically undetected but far infrared bright dusty, star forming galaxies at z>4
- This population of luminous infrared galaxies at z>4 serves as a bridge between extremely dust obscured galaxies and more typical high redshift star forming galaxies
- Far infrared observations play a significant role in uncovering hidden populations of galaxies at high redshifts
- The detection and characterization of these dusty star forming galaxies contribute to our understanding of galaxy formation and evolution in the early universe

## Summary

A recent study has shed light on a previously elusive population of dusty, star-forming galaxies at high redshifts (z>4). These galaxies are completely invisible in deep extragalactic optical surveys but have been detected through far-infrared observations. The researchers used the James Webb Space Telescope (JWST) to detect the rest-frame optical light of one such galaxy, AzTECC71, as part of the COSMOS-Web survey. AzTECC71 is among the reddest galaxies in COSMOS-Web and was previously undetected at wavelengths shorter than 850 microns. It is undetected in near-infrared observations with NIRCam/F150W and F115W filters and appears fainter in the F444W filter compared to other sub-millimeter galaxies identified in COSMOS-Web. This suggests that AzTECC71 has a lower stellar mass and higher redshift than the median dusty, star-forming galaxy. By combining deep ground- and space-based upper limits with detections in specific filters and far-infrared observations including ALMA Band 6, the researchers determined that there is a high probability (99%) that AzTECC71 is at a redshift greater than 4 (z>4), specifically with z_phot=5.7(+0.8,-0.7). The galaxy is found to be massive (logM*/Msun~10.7) and IR-luminous (logLIR/Lsun~12.7), comparable to other optically-undetected but far infrared bright dusty, star forming galaxies at z>4. This population of luminous infrared galaxies at z>4 represents an important bridge between extremely dust obscured galaxies and more typical high redshift star forming galaxies. However, their properties and characteristics are largely unconstrained due to their invisibility in optical surveys. If there are more far infrared selected galaxies like AzTECC71 that drop out of the F150W filter in COSMOS Web and have redshifts greater than 4, then the volume density of such sources may be approximately 3 - 10 times greater than previously estimated. Overall, this study highlights the significance of far infrared observations and the role they play in uncovering hidden populations of galaxies at high redshifts. The detection and characterization of these dusty star forming galaxies provide valuable insights into their stellar properties and contribute to our understanding of galaxy formation and evolution in the early universe.