# Spectroscopy from Photometry: A Population of Extreme Emission Line Galaxies at $1.7 \lesssim z \lesssim 6.7$ Selected with JWST Medium Band Filters

**Authors:** Sunna Withers, Adam Muzzin, Swara Ravindranath, Ghassan T. Sarrouh, Roberto Abraham, Yoshihisa Asada, Marusa Bradac, Gabriel Brammer, Guillaume Desprez, Kartheik Iyer, Nicholas Martis, Lamiya Mowla, Gaël Noirot, Marcin Sawicki, Victoria Strait, Chris J. Willott  
**arXiv:** [2304.11181](https://arxiv.org/abs/2304.11181)  
**Date:** 2023-04-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.11181v1/

## Key points

- Study utilizes JWST/NIRCam medium band photometry in CANUCS
- Identifies 118 Extreme Emission Line Galaxies (EELGs) within redshift range of $1.7 \lesssim z \lesssim 6.7$
- Selection based on color cuts targeting extreme $\text{[OIII] + H}\beta$ and H$\alpha$ emission
- Medium band color selections allow identification based on emission line equivalent width (EW)
- Median EW(\Ha) = 893 Å, median EW(\OIIIHb) = 1255 Å
- EELGs are compact with low stellar mass, low metallicity, minimal dust content, and high specific star formation rates
- Increase in both EW(\Ha) and EW(\OIIIHb) with increasing redshift
- Anti-correlation between EW(\Ha) and stellar mass; no correlation between EW(\OIIIHb) and stellar mass
- NIRSpec spectroscopy confirms redshifts and equivalent widths for 15 EELGs
- Advantages of using medium band photometry to study EELGs without relying on strong continuum emission
- Insights into properties and evolution of EELGs related to redshift, stellar mass, and emission line strengths

## Summary

This study utilizes JWST/NIRCam medium band photometry in a single pointing of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS) to identify 118 Extreme Emission Line Galaxies (EELGs) within the redshift range of $1.7 \lesssim z \lesssim 6.7$. The selection of these galaxies is based on specific color cuts that target extreme $\text{[OIII] + H}\beta$ and H$\alpha$ emission. The advantage of using medium band color selections is that it allows for the identification of galaxies based on their emission line equivalent width (EW), without requiring strong continuum emission. This method is particularly useful for selecting galaxies with faint or red continuum fluxes. The median equivalent widths of the identified sample are $EW(\text{H}\alpha) = 893 $ Å and $ EW(\text{[OIII] + H}\beta) = 1255 $ Å, with some objects exhibiting even higher values, such as $EW(\text{[OIII] + H}\beta) \sim 3000$ Å. These EELGs are predominantly compact in nature, characterized by low stellar mass (median $\log(M_\star/M_\odot) = 8.03$), low metallicity (median $Z = 0.14 Z_\odot$), minimal dust content (median $A_V = 0.18$ mag), and high specific star formation rates (median $SSFR = 1.18 \times 10^{-8}/yr$). Furthermore, an analysis reveals several interesting trends: there is a clear increase in both EW(\Ha) and EW(\OIIIHb) with increasing redshift; an anti-correlation between EW(\Ha) and stellar mass; however, no correlation between EW(\OIIIHb) and stellar mass. To validate the accuracy and efficiency of their color selections, the authors present NIRSpec spectroscopy results for 15 EELGs in their sample which confirm the redshifts and equivalent widths calculated from the medium bands. In conclusion, this study demonstrates the advantages of using medium band photometry to identify and study EELGs across a wide range of redshifts without relying on strong continuum emission which allows for including galaxies with faint or red continuum fluxes. The findings also provide valuable insights into the properties and evolution of EELGs related to redshift, stellar mass, and emission line strengths.