A first look at a complete view of spatially resolved star formation at 1  <  z  <  1.8 with JWST NGDEEP+FRESCO slitless spectroscopy

¹ Cosmic Dawn Center, Copenhagen, Denmark
² Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200, Copenhagen, Denmark
³ Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg, Germany
⁴ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁵ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77845-4242, USA
⁶ Centro de Astrobiología (CAB), CSIC-INTA, Carretera de Ajalvir km 4, Torrejón de Ardoz, 28850, Madrid, Spain
⁷ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290, Versoix, Switzerland
⁸ Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA
⁹ Department of Astronomy, University of Washington, Seattle, WA 98195, USA
¹⁰ University of Massachusetts Amherst, 710 North Pleasant Street, Amherst, MA 01003-9305, USA
¹¹ Astronomy Department, Yale University, 52 Hillhouse Ave, New Haven, CT 06511, USA
¹² Department of Astronomy, The University of Texas at Austin, Austin, TX, USA
¹³ Cosmic Frontier Center, The University of Texas at Austin, Austin, TX 78712, USA
¹⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁵ Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA
¹⁶ Institute of Science and Technology Austria (ISTA), Am Campus 1, A-3400, Klosterneuburg, Austria
¹⁷ Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH, UK
¹⁸ Institute of Space Sciences and Astronomy, University of Malta, Msida MSD 2080, Malta

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Received: 21 November 2025
Accepted: 27 February 2026

Abstract

The previously inaccessible star formation tracer Paschen-Alpha (Paα) can now be spatially resolved by JWST NIRCam slitless spectroscopy in distant galaxies up to cosmic noon. In the first study of its kind, we combine JWST NGDEEP NIRISS and FRESCO NIRCam slitless spectroscopy to provide the first direct comparison of spatially resolved dust-obscured (traced by Paα) versus unobscured (traced by Hα) star formation across the main sequence. We stacked Paα and Hα emission-line maps, along with stellar continuum images at both wavelengths of 31 galaxies at 1 < z < 1.8 in three bins of stellar mass spanning 7.7 ≤ log(M_*/M_⊙) < 11. Surface brightness profiles were measured and equivalent width (EW) profiles computed. Increasing Paα and Hα EW profiles with galactocentric radius across all stellar masses probed provides direct evidence for the inside-out growth of galaxies both via dust-obscured and unobscured star formation for the first time. For galaxies predominantly on the main sequence (log(M_*/M_⊙)≥8.8), a weakly positive (0.1 ± 0.1) Paα/Hα line profile gradient as a function of radius is found at 8.8 ≤ log(M_*/M_⊙) < 9.9, with a negative (−0.4 ± 0.1) Paα/Hα line profile gradient as a function of radius found at the highest stellar masses of 9.9 ≤ log(M_*/M_⊙) < 11.0. Low-mass galaxies (7.7 ≤ log(M_*/M_⊙) < 8.8) with predominantly high specific star formation rates relative to the main sequence are also found to have a negative (−0.5 ± 0.1) Paα/Hα line profile gradient as a function of radius. Our results demonstrate that while inside-out growth via star formation is ubiquitous across the main sequence just after cosmic noon, centrally concentrated dust attenuation is not. Along with other recent work in the literature, our findings now motivate future studies of resolved SFR and dust attenuation profiles in large samples of individual cosmic noon galaxies across the main sequence, aimed at understanding the intrinsic scatter in spatially resolved star formation.