apjThe Astrophysical JournalApJAstrophys. J.0004-637X1538-4357The American Astronomical Societyapjadddb110.3847/1538-4357/adddb1adddb1AAS63272310Galaxies and CosmologyMedium-band Astrophysics with the Grism of NIRCam In Frontier Fields (MAGNIF): Spectroscopic Census of Hα Luminosity Functions and Cosmic Star Formation at z ∼ 4.5 and 6.30000-0003-0964-7188FuShuqi120000-0002-4622-6617SunFengwu30000-0003-4176-6486JiangLinhua120000-0001-6052-4234LinXiaojing450000-0001-9065-3926DiegoJose M.60000-0001-6278-032XFurtakLukas J.70000-0003-1974-8732JauzacMathilde8910110000-0002-6610-2048KoekemoerAnton M.120000-0001-6251-649XLiMingyu40000-0003-3484-399XOguriMasamune13140000-0001-6804-0621PatelNency R.890000-0001-9262-9997WillmerChristopher N. A.50000-0001-8156-6281WindhorstRogier A.150000-0002-0350-4488ZitrinAdi70000-0002-8686-8737Bauer’sFranz E.160000-0002-3805-0789ChenChian-Chou170000-0003-1060-0723ChenWenlei180000-0003-0202-0534ChengCheng190000-0003-1949-7638ConseliceChristopher J.200000-0002-2929-3121EisensteinDaniel J.30000-0003-1344-9475EgamiEiichi50000-0002-8726-7685EspadaDaniel21220000-0003-3310-0131FanXiaohui50000-0001-7201-5066FujimotoSeiji230000-0003-4512-8705HsiaoTiger Yu-Yang312240000-0002-5768-738XJinXiangyu50000-0002-4052-2394KohnoKotaro25260000-0002-7633-2883LagattutaDavid J.890000-0001-5951-459XLiZihao27280000-0003-3762-7344LiuWeizhe50000-0002-2316-8370Miralda-EscudéJordi2930310000-0001-9442-1217NingYuanhang320000-0002-8224-4505TacchellaSandro33340000-0003-0747-1780TeeWei Leong50000-0003-1937-0573UmehataHideki35360000-0002-7633-431XWangFeige370000-0001-7592-7714YanHaojing380000-0003-3307-7525ZhuYongda5 Department of Astronomy, School of Physics, Peking University, Beijing 100871, People’s Republic of China Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People’s Republic of China Center for Astrophysics ∣ Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA Department of Astronomy, Tsinghua University, Beijing 100084, People’s Republic of China Steward Observatory, University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721, USA Instituto de Física de Cantabria (CSIC-UC). Avda. Los Castros s/n. 39005 Santander, Spain Department of Physics, Ben-Gurion University of the Negev, P.O. Box 653, Be’er-Sheva 84105, Israel Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK Astrophysics Research Centre, University of KwaZulu-Natal, Westville Campus, Durban 4041, South Africa School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Westville Campus, Durban 4041, South Africa Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Center for Frontier Science, Chiba University, 1-33 Yayoicho, Inage, Chiba 263-8522, Japan Department of Physics, Graduate School of Science, Chiba University, 1-33 Yayoicho, Inage, Chiba 263-8522, Japan School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-6004, USA Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), No. 1, Sec. 4, Roosevelt Road, Taipei 106319, Taiwan Department of Physics, Oklahoma State University, 145 Physical Sciences Bldg, Stillwater, OK 74078, USA Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, People’s Republic of China Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Oxford Road, Manchester M13 9PL, UK Departamento de Física Teórica y del Cosmos, Campus de Fuentenueva, Edificio Mecenas, Universidad de Granada, E-18071, Granada, Spain Instituto Carlos I de Física Teórica yComputacional, Facultad de Ciencias, E-18071, Granada, Spain Department of Astronomy, University of Texas at Austin, Austin, TX, USA Center for Astrophysical Sciences, Department of Physics and Astronomy, The Johns Hopkins University, 3400 N Charles St. Baltimore, MD 21218, USA Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Cosmic Dawn Center (DAWN), Denmark Niels Bohr Institute, University of Copenhagen, Jagtvej 128, DK2200 Copenhagen N, Denmark Institut de Ciències del Cosmos, Universitat de Barcelona, 08028 Barcelona, Spain Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain Institut d’Estudis Espacials de Catalunya, 08860 Barcelona, Spain Department of Scientific Research, Beijing Planetarium, Beijing 100044, People’s Republic of China Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK Cavendish Laboratory—Astrophysics Group, University of Cambridge, 19 JJ Thomson Avenue, Cambridge, CB3 0HE, UK Institute for Advanced Research, Nagoya University, Furocho, Chikusa, Nagoya 464-8602, Japan Department of Physics, Graduate School of Science, Nagoya University, Furocho, Chikusa, Nagoya 464-8602, Japan Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109, USA Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA 100720250807202508072025987218605032025140520252505202525052025© 2025. The Author(s). Published by the American Astronomical Society.2025 Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Abstract

We measure Hα luminosity functions (LFs) at redshifts z ∼ 4.5 and 6.3 using the JWST Medium-band Astrophysics with the Grism of NIRCam In Frontier fields (MAGNIF) 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 Hubble Space Telescope 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 observed and dust-corrected Hα LFs at the two redshifts. 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. They correspond to star formation rates of ∼0.1 and 1.7 M⊙ yr−1, respectively. 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 star formation rate densities are 0.058−0.006+0.008M⊙yr−1Mpc−3 at z ∼ 4.5 and 0.025−0.007+0.009M⊙yr−1Mpc−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 propagated from the lens models, cosmic variance, and active galactic nucleus contribution, and we find that they have a negligible impact on the above results.

unified-astronomy-thesaurushttp://astrothesaurus.org/uat/734High-redshift galaxies734http://astrothesaurus.org/uat/2291James Webb Space Telescope2291http://astrothesaurus.org/uat/1569Star formation1569http://astrothesaurus.org/uat/942Luminosity function942http://astrothesaurus.org/uat/1643Strong gravitational lensing1643crossmarkyesdataset Acknowledgments

We acknowledge support from the National Key R&D Program of China (2022YFF0503401) and the National Science Foundation of China (12225301). F.S., E.E., D.J.E., and Y.Z. acknowledge funding from JWST/NIRCam contract to the University of Arizona, NAS 5-02105. F.E.B. acknowledges support from ANID-Chile BASAL CATA FB210003, FONDECYT Regular 1241005, and Millennium Science Initiative, AIM23-0001. M.O. acknowledges support from JSPS KAKENHI grant Nos. JP23K22531, JP22K21349, JP20H05856. R.A.W. acknowledges support from NASA JWST Interdisciplinary Scientist grants NAG5-12460, NNX14AN10G, and 80NSSC18K0200 from GSFC. F.W. acknowledges support from NSF award AST-2513040. A.Z. acknowledges support by grant No. 2020750 from the United States-Israel Binational Science Foundation (BSF) and grant No. 2109066 from the United States National Science Foundation (NSF); and by the Israel Science Foundation grant No. 864/23. C.-C.C. acknowledges support from the National Science and Technology Council of Taiwan (111-2112-M-001-045-MY3), as well as Academia Sinica through the Career Development Award (AS-CDA-112-M02). M.J. and N.P. are supported by the United Kingdom Research and Innovation (UKRI) Future Leaders Fellowship “Using Cosmic Beasts to uncover the Nature of Dark Matter” (grant No. MR/X006069/1). K.K. acknowledges support from JSPS KAKENHI grant Nos. JP22H04939, JP23K20035, and JP24H00004. C.C. is supported by Chinese Academy of Sciences South America Center for Astronomy (CASSACA) Key Research Project E52H540301 and by the National Natural Science Foundation of China, No. 11933003, 12173045. We thank Weston Eck, our JWST-GO-2883 program coordinator, for the valuable support for our observations. F.S. acknowledges helpful discussions with James Trussler.

This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program #1176, 1199, 1208, 1324, 2514, 2561, 2756, 2883, 3362, 3516, 3538, 4111. The authors acknowledge the 1324 (GLASS), 2514 (PANORAMIC), 2561 (UNCOVER), 3362 (Technicolor), 3516 (ALT), 3538, and 4111 (MegaScience) for developing their observing program with a zero-exclusive-access period. Support for program #2883 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127.

Facilities: JWST (NIRCam and NIRISS), HST (ACS).

Software: astropy (The Astropy Collaboration et al. 2013, 2018, 2022), photutils (L. Bradley et al. 2024), cigale (M. Boquien et al. 2019), emcee (D. Foreman-Mackey et al. 2013), JWST (H. Bushouse et al. 2023), Lenstool (E. Jullo et al. 2007), Webbpsf (M. D. Perrin et al. 2014).