JWST Observations of SN 2024ggi. II. NIRSpec Spectroscopy and CO Modeling at +285–385 Days past the Explosion

Mera, T ORCID: 0000-0001-5888-2542, Ashall, C ORCID: 0000-0002-5221-7557, Hoeflich, P ORCID: 0000-0002-4338-6586, Medler, K ORCID: 0000-0001-7186-105X, Shahbandeh, M ORCID: 0000-0002-9301-5302, Burns, CR ORCID: 0000-0003-4625-6629, Baron, E ORCID: 0000-0001-5393-1608, DerKacy, JM ORCID: 0000-0002-7566-6080, Morrell, N, Lu, J ORCID: 0000-0002-3900-1452, Hinkle, JT ORCID: 0000-0001-9668-2920, Mazzali, PA ORCID: 0000-0001-6876-8284, Fereidouni, E ORCID: 0009-0001-9148-8421, Pfeffer, CM ORCID: 0000-0002-7305-8321, Shiber, S ORCID: 0000-0001-6107-0887, Temim, T ORCID: 0000-0001-7380-3144, Galbany, L ORCID: 0000-0002-1296-6887, Coulter, DA ORCID: 0000-0003-4263-2228, Ferrari, L ORCID: 0009-0000-6303-4169, Hoogendam, WB ORCID: 0000-0003-3953-9532 et al (2026) JWST Observations of SN 2024ggi. II. NIRSpec Spectroscopy and CO Modeling at +285–385 Days past the Explosion. The Astrophysical Journal, 997 (2). ISSN 0004-637X

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Abstract

We present James Webb Space Telescope (JWST) Near-Infrared Spectrograph observations of SN 2024ggi, spanning wavelengths of 1.7–5.5 μm at +285.51 and +385.27 days postexplosion. These nebular spectra are dominated by asymmetric emission lines from atomic species including H, Ca, Ar, C, Mg, Ni, Co, and Fe, indicative of an aspherical explosion. The other strong features are molecular CO vibrational bands from the fundamental and first overtone. We introduce a novel, data-driven approach using non–local thermodynamic equilibrium three-dimensional (3D) radiative transfer simulations to model the CO emission with high fidelity. This method enables us to constrain the 3D CO distribution and its radial temperature structure. CO formation is found to occur prior to day +285, with subsequent evolution characterized by progressive evaporation. The CO mass decreases from approximately 8.7 to 1.3 ×10−3M⊙, while the average temperature drops from ≈2900 to ≈2500 K. Concurrently, the CO distribution transitions from nearly homogeneous to highly clumped (density contrast increasing from fc ≈ 1.2 to 2). The minimum velocity of the CO-emitting region remains nearly constant (v1 ≈ 1200 to 1100 km s−1), significantly above the receding photosphere velocity (vph ≈ 500 km s−1), suggesting the photosphere resides within Si-rich layers. However, the temperature profile indicates that only a narrow zone reaches the conditions necessary for SiO formation. Due to a lack of observational constraints, SiO clumping is not modeled, and thus, synthetic SiO profiles for mass estimates are not highlighted. We discuss the implications of these findings for dust formation processes in SN 2024ggi.

Item Type:	Article
Uncontrolled Keywords:	5109 Space Sciences; 51 Physical Sciences; 5101 Astronomical Sciences; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	1 December 2025
Date of first compliant Open Access:	5 June 2026
Date Deposited:	05 Jun 2026 10:32
Last Modified:	05 Jun 2026 10:32
DOI or ID number:	10.3847/1538-4357/ae317e
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28747

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