2025/03/05 by Shuqi Fu, Fengwu Sun, Fu, Shuqi +73 · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2503.03829
openalex publication_date 2025/03/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We measure Hα luminosity functions (LFs) at redshifts z ∼ 4.5 and 6.3 using the JWST MAGNIF (Medium-band Astrophysics with the Grism of NIRCam In Frontier fields) survey. MAGNIF obtained NIRCam grism spectra with the F360M and F480M filters in four Frontier Fields. We identify 248 Hα emitters based on the grism spectra and photometric redshifts from combined HST and JWST imaging data. The numbers of the Hα emitters show a large field-to-field variation, highlighting the necessity of multiple fields to mitigate cosmic variance. We calculate both observed and dust-corrected Hα LFs in the two redshift bins. Thanks to the gravitational lensing, the measured Hα LFs span three orders of magnitude in luminosity, and the faint-end luminosity reaches LHα ∼ 1040.3 erg s-1 at z ∼ 4.5 and 1041.5 erg s-1 at z ∼ 6.3, corresponding to star-formation rates (SFRs) of ∼ 0.1 and 1.7 M_\odot yr-1. We conclude no or weak redshift evolution of the faint-end slope of Hα LF across z≃0.4-6.3, and the comparison with the faint-end slopes of UV LF indicates stochastic star formation history among low-mass Hα emitters. The derived cosmic SFR densities are 0.058+0.008-0.006 M_\odot yr-1 Mpc-3 at z ∼ 4.5 and 0.025+0.009-0.007 M_\odot yr-1 Mpc-3 at z ∼ 6.3. These are approximately 2.2 times higher than previous estimates based on dust-corrected UV LFs, but consistent with recent measurements from infrared surveys. We discuss uncertainties in the Hα LF measurements, including those propagate from the lens models, cosmic variance, and AGN contribution.