An Hα view of galaxy buildup in the first 2 Gyr: Luminosity functions at z  ∼  4−6.5 from NIRCam/grism spectroscopy

¹ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
² Cosmic Dawn Center (DAWN), Copenhagen, Denmark
³ Niels Bohr Insitute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen, Denmark
⁴ Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
⁵ Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800 9700 AV Groningen, The Netherlands
⁶ Department of Physics and Astronomy, Tufts University, 574 Boston Avenue, Medford, MA 02155, USA
⁷ MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Ave., Cambridge, MA 02139, USA
⁸ Institute of Astronomy, Kharkiv National University, 4 Svobody Sq., Kharkiv 61022, Ukraine
⁹ European Southern Observatory, Karl-Schwarzschildstrasse 2, D-85748 Garching bei München, Germany
¹⁰ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
¹¹ Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USA
¹² Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
¹³ Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
¹⁴ Department of Astronomy, University of Wisconsin–Madison, 475 N. Charter St., Madison, WI 53706, USA
¹⁵ Department for Astrophysical and Planetary Science, University of Colorado, Boulder, CO 80309, USA
¹⁶ Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA
¹⁷ Departament d’Astronomia i Astrofìsica, Universitat de València, C. Dr. Moliner 50, E-46100 Burjassot, València, Spain
¹⁸ Unidad Asociada CSIC “Grupo de Astrofísica Extragaláctica y Cosmología” (Instituto de Física de Cantabria – Universitat de València), Valencia, Spain

^⋆ Corresponding author; alba.covelopaz@unige.ch

Received: 24 September 2024
Accepted: 14 January 2025

Abstract

The Hα nebular emission line is an optimal tracer for recent star formation in galaxies. With the advent of JWST, this line has recently become observable at z > 3 for the first time. We present a catalog of 1050 Hα emitters at 3.7 < z < 6.7 in the GOODS fields obtained from a blind search in JWST NIRCam/grism data. We made use of the FRESCO survey’s 124 arcmin² of observations in GOODS-North and GOODS-South with the F444W filter, probing Hα at 4.9 < z < 6.7, and the CONGRESS survey’s 62 arcmin² of observations in GOODS-North with F356W, probing Hα at 3.8 < z < 5.1. We found an overdensity with 98 sources at z ∼ 4.4 in GOODS-N, and confirmed previously reported overdensities at z ∼ 5.2 in GOODS-N and at z ∼ 5.4 and z ∼ 5.9 in GOODS-S. We computed the observed Hα luminosity functions (LFs) in three bins centered at z ∼ 4.45, 5.30, and 6.15, which are the first such measurements at z > 3 obtained based purely on spectroscopic data, robustly tracing galaxy star formation rates (SFRs) beyond the peak of the cosmic star formation history. We compared our results with theoretical predictions from three different simulations and found good agreement at z ∼ 4 − 6. The UV LFs of this spectroscopically confirmed sample are in good agreement with pre-JWST measurements obtained with photometrically selected objects. Finally, we derived SFR functions and integrated them to compute the evolution of the cosmic SFR densities across z ∼ 4 − 6, finding values in good agreement with recent UV estimates from Lyman-break galaxies, which imply a continuous decrease in SFR density by a factor of three over z ∼ 4 to z ∼ 6. Our work shows the power of NIRCam grism observations to efficiently provide new tests for early galaxy formation models based on emission line statistics.