The Sunburst Arc with JWST
T. Emil Rivera-Thorsen, J. Chisholm, Brian Welch, Jane R. Rigby, Taylor A. Hutchison, Michael Florian, Keren Sharon, S. Choe, H. Dahle, Matthew Bayliss, Gourav Khullar, Michael D. Gladders, Matthew Hayes, Angela Adamo, M. Riley Owens, K. Kim
Abstract
We report the detection of a population of Wolf-Rayet (WR) stars in the Sunburst Arc, a strongly gravitationally lensed galaxy at redshift z = 2.37. As the brightest known lensed galaxy, the Sunburst Arc has become an important cosmic laboratory for studying star and cluster formation, Lyman α (Ly α ) radiative transfer, and Lyman continuum (LyC) escape. Here, we present the first results of JWST/NIRSpec IFU observations of the Sunburst Arc, focusing on a stacked spectrum of the 12-fold imaged Sunburst LyC-emitting (LCE) cluster. In agreement with previous studies, we find that the Sunburst LCE cluster is a very massive, compact star cluster with M dyn = (9 ± 1)×10 6 M ⊙ . Our age estimate of 4.2–4.5 Myr is much larger than the crossing time of t cross = 183 ± 9 kyr, indicating that the cluster is dynamically evolved and consistent with it being gravitationally bound. We find a significant nitrogen enhancement of the low ionization state interstellar medium (ISM), with log(N/O) = − 0.74 ± 0.09, which is ≈0.8 dex above typical values for H II regions of a similar metallicity in the local Universe. We find broad stellar emission complexes around He II λ 4686 and C IV λ 5808 with associated nitrogen emission; this is the first time WR signatures have been directly observed at redshifts above ∼0.5. The strength of the WR signatures cannot be reproduced by stellar population models that only include single-star evolution. While models with binary evolution better match the WR features, they still struggle to reproduce the nitrogen-enhanced WR features. JWST reveals the Sunburst LCE cluster to be a highly ionized proto-globular cluster with low oxygen abundance and extreme nitrogen enhancement that hosts a population of WR stars, likely including a previously suggested population of very massive stars (VMSs), which together are rapidly enriching the surrounding medium.