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
T. Emil Rivera-Thorsen, J. Chisholm, B. Welch, J. R. Rigby, T. Hutchison, M. Florian, K. Sharon, S. Choe, H. Dahle, M. B. Bayliss, G. Khullar, M. Gladders, M. Hayes, A. Adamo, M. R. Owens, K. Kim
arXiv:2404.08884v1 Announce Type: new
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 $alpha$ 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 $M_{text{dyn}} = (9pm1) times 10^{6} M_{odot}$, Our age estimate of 4.2–4.5 Myr is much larger than the crossing time of $t_{text{cross}} = 183 pm 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 $log(N/O) = -0.74 pm 0.09$, which is $approx 0.8$ dex above typical values for H II regions of similar metallicity in the local Universe. We find broad stellar emission complexes around He II$lambda 4686$ and C IV$lambda 5808$ with associated nitrogen emission — this is the first time WR signatures have been directly observed at redshifts above $sim 0.5$. 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.arXiv:2404.08884v1 Announce Type: new
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 $alpha$ 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 $M_{text{dyn}} = (9pm1) times 10^{6} M_{odot}$, Our age estimate of 4.2–4.5 Myr is much larger than the crossing time of $t_{text{cross}} = 183 pm 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 $log(N/O) = -0.74 pm 0.09$, which is $approx 0.8$ dex above typical values for H II regions of similar metallicity in the local Universe. We find broad stellar emission complexes around He II$lambda 4686$ and C IV$lambda 5808$ with associated nitrogen emission — this is the first time WR signatures have been directly observed at redshifts above $sim 0.5$. 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.

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