2023ApJ...957...77P

Strong lensing offers a precious opportunity for studying the formation and early evolution of super star clusters that are rare in our cosmic backyard. The Sunburst Arc, a lensed Cosmic Noon galaxy, hosts a young super star cluster with escaping Lyman continuum radiation. Analyzing archival Hubble Space Telescope images and emission line data from Very Large Telescope/MUSE and X-shooter, we construct a physical model for the cluster and its surrounding photoionized nebula. We confirm that the cluster is ≲4 Myr old, is extremely massive M_⋆ ∼ 10⁷M_⊙, and yet has a central component as compact as several parsecs, and we find a gas-phase metallicity Z = (0.22 ± 0.03)Z_⊙. The cluster is surrounded by ≳10⁵M_⊙ of dense clouds that have been pressurized to P ∼ 10⁹ K cm^–3 by perhaps stellar radiation at within 10 pc. These should have large neutral columns N_HI > 10^22.8 cm^–2 to survive rapid ejection by radiation pressure. The clouds are likely dusty as they show gas-phase depletion of silicon, and may be conducive to secondary star formation if N_HI > 10²⁴ cm^–2 or if they sink farther toward the cluster center. Detecting strong [N III]λλ 1750,1752, we infer heavy nitrogen enrichment $\mathrm{log}({\rm{N}}/{\rm{O}})=-{0.21}_{-0.11}^{+0.10}$. This requires efficiently retaining ≳500 M_⊙ of nitrogen in the high-pressure clouds from massive stars heavier than 60 M_⊙ up to 4 Myr. We suggest a physical origin of the high-pressure clouds from partial or complete condensation of slow massive star ejecta, which may have an important implication for the puzzle of multiple stellar populations in globular clusters.