The JWST Emission Line Survey (JELS): A narrow-band determination of the H alpha Luminosity Function and Cosmic Star Formation into the Epoch of Reionization

The recent star-formation activity in galaxies can be optimally traced by the H α emission line, with the resulting H α luminosity function (LF) at a given epoch providing a reliable probe of cosmic star formation. We present the first narrow-band determined H α LF into the Epoch of Reionization (EoR) at z about6.1, using 39 H α emitters selected from the JWST Emission Line Survey (JELS). The observed and dust-corrected LFs are broadly consistent with recent slitless spectroscopic measurements but show notable discrepancies with predictions from cosmological simulations, likely reflecting differences in emission-line and dust modelling. Fits combining multiple LF datasets help constrain the high-redshift faint-end slope of the H α LF (-1.79<α<-1.62), but there remains uncertainty in its evolution with redshift. Integrating the JELS dust-corrected H α LFs yields a star-formation rate density of 10(ρ,/,)=-1.93,+0.14-0.12 or-2.00,+0.16-0.10, assuming a continuum-to-line extinction ratios η=A/A=1 and 0.44, respectively. Both measurements are consistent within uncertainties with previous results using standard assumptions for the LF integration limit (L) and SFR calibration constant κ, despite the uncertainties in the dust corrections. We explore the metallicity dependence of κ and find ρ decreases 0.43 dex compared to the fiducial result and is no longer consistent with UV-determined ρ at z about6. This work highlights the importance of narrow-band surveys in probing the faint H α population and providing new constraints on cosmic star-formation activity into the EoR.