The JWST Emission Line Survey (JELS): An untargeted search for H$\hat{I}\pm$ emission line galaxies at $z>6$ and their physical properties

Abstract

We present the first results of the JWST Emission Line Survey (JELS). Utilising the first NIRCam narrow-band imaging at 4.7$\hat{I}¼$m, over 63 arcmin${}^2$ in the PRIMER/COSMOS field, we identified 609 emission line galaxy candidates. From these, we robustly selected 35 H$\hat{I}\pm$ star-forming galaxies at $z\sim 6.1$, with H$\hat{I}\pm$ star-formation rates ($\mathrm{SF}{\mathrm{R}}_{\mathrm{H}\hat{\mathrm{I}}\pm }$) $\sim 0.9-15{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$. Combining our unique H$\hat{I}\pm$ sample with the exquisite panchromatic data in the field, we explored their physical properties and star-formation histories, and compared these to a broad-band selected sample at $z\sim 6$ which offered vital new insights into the nature of high-redshift galaxies. UV-continuum slopes (${\hat{I}}^2$) were considerably redder for our H$\hat{I}\pm$ sample ($⟨{\hat{I}}^2⟩\sim -1.92$) compared to the broad-band sample ($⟨{\hat{I}}^2⟩\sim -2.35$). This was not due to dust attenuation as our H$\hat{I}\pm$ sample was relatively dust-poor (median $A_V=0.23$); instead, we argued the reddened slopes could be due to nebular continuum. We compared $\mathrm{SF}{\mathrm{R}}_{\mathrm{H}\hat{\mathrm{I}}\pm }$ and the UV-continuum-derived $\mathrm{SF}{\mathrm{R}}_{\mathrm{UV}}$ to SED-fitted measurements averaged over canonical timescales of 10 and 100 Myr ($\mathrm{SF}{\mathrm{R}}_{10}$ and $\mathrm{SF}{\mathrm{R}}_{100}$). We found an increase in recent SFR for our sample of H$\hat{I}\pm$ emitters, particularly at lower stellar masses ($<10^9{\mathrm{M}}_{\odot }$). We also found $\mathrm{SF}{\mathrm{R}}_{\mathrm{H}\hat{\mathrm{I}}\pm }$ strongly traced SFR averaged over 10 Myr timescales, whereas the UV-continuum over-predicts SFR on 100 Myr timescales at low stellar masses. These results point to our H$\hat{I}\pm$ sample undergoing `bursty' star formation. Our F356W $z\sim 6$ sample showed a larger scatter in $\mathrm{SF}{\mathrm{R}}_{10}/SF{\mathrm{R}}_{100}$ across all stellar masses, which highlighted how narrow-band photometric selections of H$\hat{I}\pm$ emitters are key to quantifying the burstiness of star-formation activity.

29 pages, 19 figures, Accepted for publication in MNRAS after minor revisions