James Webb Space Telescope Feed Post

Harvard ADS: The JWST Emission Line Survey (JELS): An untargeted search for H\alpha emission line galaxies at z > 6 and their physical properties

Paper abstract: We present the first results of the JWST Emission Line Survey (JELS). Utilising the first NIRCam narrow-band imaging at 4.7\mum, over 63 arcmin^{2} in the PRIMER/COSMOS field, we have identified 609 emission line galaxy candidates. From these, we robustly selected 35 H\alpha star-forming galaxies at z ~ 6.1, with H\alpha star-formation rates (\rm{SFR_{H\alpha}}) of ~0.9-15\ \rm{M_{\odot} yr^{-1}}. Combining our unique H\alpha sample with the exquisite panchromatic data in the field, we explore their physical properties and star-formation histories, and compare these to a broad-band selected sample at z~ 6 to offer vital new insight into the nature of high-redshift galaxies. UV-continuum slopes (\beta) are considerably redder for our H\alpha sample (\langle\beta\rangle~-1.92) compared to the broad-band sample (\langle\beta\rangle~-2.35). This is not due to dust attenuation as our H\alpha sample is relatively dust-poor (median A_V=0.23); instead, we argue that the reddened slopes could be due to nebular continuum. We compared \rm{SFR_{H\alpha}} and the UV-continuum-derived \rm{SFR_{UV}} to SED-fitted measurements averaged over canonical timescales of 10 and 100 Myr (\rm{SFR_{10}} and \rm{SFR_{100}}). We find an increase in recent SFR for our sample of H\alpha emitters, particularly at lower stellar masses (<10^9 \rm{M_{\odot}}). We also find that \rm{SFR_{H\alpha}} strongly traces 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\alpha sample undergoing `bursty' star formation. Our F356W z ~ 6 sample show a larger scatter in \rm{SFR_{10}/SFR_{100}} across all stellar masses, highlighting how narrow-band photometric selections of H\alpha emitters are key to quantifying the burstiness of star-formation activity.