Early results from GLASS-JWST. VI: Extreme rest-optical equivalent widths detected in NIRISS Wide Field Slitless Spectroscopy

TL;DR

This study uses JWST/NIRISS WFSS to measure rest-optical emission line equivalent widths in star-forming galaxies at z=1-3.4, revealing a significant fraction of extreme emission line galaxies and demonstrating JWST's capabilities in crowded environments.

Contribution

First measurement of [OIII]$ m{ extlambda}5007$ EW distribution in galaxies at z=1-3.4 using JWST/NIRISS WFSS, including faint galaxies, and establishing a correlation with H$eta$ EW.

Findings

12% of galaxies have EW > 750A, indicating extreme emission line activity.

Strong correlation between H$eta$ and [OIII]$ m{ extlambda}5007$ EWs.

JWST/NIRISS can observe faint galaxies in crowded cluster fields.

Abstract

Wide Field Slitless Spectroscopy (WFSS) provides a powerful tool for detecting strong line emission in star forming galaxies (SFGs) without the need for target pre-selection. As part of the GLASS-JWST-ERS program, we leverage the near-infrared wavelength capabilities of NIRISS ($1-2.2\mu$m) to observe rest-optical emission lines out to $\rm{z}\sim 3.4$, to a depth and with a spatial resolution higher than ever before (H$\alpha$ to z<2.4; [OIII]+H$\beta$ to z<3.4). In this letter we constrain the rest-frame [OIII]$\lambda5007$ equivalent width (EW) distribution for a sample of 76 $1<\rm{z}<3.4$ SFGs in the Abell 2744 Hubble Frontier Field and determine an abundance fraction of extreme emission line galaxies with EW$>750$A in our sample to be $12\%$. We determine a strong correlation between the measured H$\beta$ and [OIII]$\lambda5007$ EWs, supporting that the high [OIII]$\lambda5007$ EW objects require massive stars in young stellar populations to generate the high energy photons needed to doubly ionise oxygen. We extracted spectra for objects up to 2 mag fainter in the near-infrared than previous WFSS studies with the Hubble Space Telescope. Thus, this work clearly highlights the potential of JWST/NIRISS to provide high quality WFSS datasets in crowded cluster environments.