James Webb Space Telescope Feed Post

The Sunburst Arc with JWST: Detection of Wolf-Rayet stars injecting nitrogen into a low-metallicity, z=2.37 proto-globular cluster leaking ionizing photons

Overview of the arc. Left: NIRCam RGB composite of the N and NW arc segments, with R,G,B being F115W, F200W, and F444W, respectively, together covering the rest-frame wavelength range 3400–13000 Å. Cyan, magenta and yellow dashed overlays show the approximate footprints of the three NIRSpec pointings 1, 2 and 3, respectively. Orange arrows show the images of the gravitationally lensed LCE cluster which were included in the stacked spectrum. Right: NIRSpec IFU continuum images of pointings 1 (top right) and combined pointings 2+3 (bottom right); created from a median stacking along the spectral axis of the F100L/G140H cubes. Orange circles mark the images of the LCE cluster included in the stacked spectrum. 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 a radiative transfer, and Lyman Continuum (LyC) escape. Here, we present the first results of JWST/NIRCam imaging and NIRSpec IFU observations of the Sunburst Arc, focusing on a stacked spectrum of the 12-fold imaged LyC-emitting (Sunburst LCE) cluster. In agreement with previous studies, we find that the cluster is massive and compact, with Mdyn=(9±1)×106M?, Our age estimate of 4.2--4.5 Myr is much larger than the crossing time of tcross=183±9 kyr, indicating that the cluster is dynamically evolved and consistent with being gravitationally bound. We find a significant nitrogen enhancement of the low ionization state ISM, with log(N/O)=-0.74±0.09, which is ˜0.8 dex above typical values for H II regions of similar metallicity in the local Universe. We find broad stellar emission complexes around He II?4686 and C IV?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 to be a highly ionized, proto-globular cluster with low oxygen abundance and extreme nitrogen enhancement that hosts a population of Wolf-Rayet stars, and possibly Very Massive stars (VMSs), which are rapidly enriching the surrounding medium.