The Lyman-continuum-leaking super star cluster in the Sunburst Arc and its surrounding nebula

Abstract

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 HST images and emission line data from VLT/MUSE and X-shooter, we construct a physical model for the cluster and its surrounding photoionized nebula. We confirm that the cluster is ∼ 3-4 Myr old, is extremely massive M ∼ 10 7 M and yet has a central component as compact as several parsecs, and we find a metallicity Z = (0.26±0.03) Z . The cluster is surrounded by 10 5 M of dense clouds that have been pressurized to P ∼ 10 9 K cm −3 by perhaps stellar radiation at within ten parsecs. These should have large neutral columns N HI > 10 22.5 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 > 10 24 cm −2 or if they sink further toward the cluster center. Detecting strong N III]λλ1750,1752, we infer heavy nitrogen enrichment log(N/O) = −0.23 +0.08 −0.11 . 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 important implication for the puzzle of multiple stellar populations in globular clusters.

GN-z11 in context: possible signatures of globular cluster precursors at redshift 10

“…> 2 in GN-z11 and Mrk 996; Figure 2 and Pascale et al 2023). Pascale et al (2023) conclude from a detailed analysis (leveraging strong constraints on the hydrogen column density and cluster radius unavailable for GN-z11) that this cluster is host to 10 5 M of dense, highly nitrogen enriched (inferring log 10 (N/O) = −0.2 comparable to our gas-phase measurement in GN-z11) material which is likely capable of forming a globular cluster. The similarity of GN-z11 to spectra of the Sunburst cluster (and Mrk 996) is particularly striking given that GN-z11 is at least an order of magnitude more massive, in both photometrically estimated stellar mass and inferred quantity of nitrogenenriched gas involved.…”

“…In particular, strong N III] λ1750 emission is apparent, though at a somewhat lower flux relative to O III] than in these systems (N III] λ1750/O III] λλ1661, 1666 near 0.9, c.f. > 2 in GN-z11 and Mrk 996; Figure 2 and Pascale et al 2023). Pascale et al (2023) conclude from a detailed analysis (leveraging strong constraints on the hydrogen column density and cluster radius unavailable for GN-z11) that this cluster is host to 10 5 M of dense, highly nitrogen enriched (inferring log 10 (N/O) = −0.2 comparable to our gas-phase measurement in GN-z11) material which is likely capable of forming a globular cluster.…”

“…First, a super star cluster complex in the Sunburst Arc stands out as among the most instructive comparison points. We return to discuss the implications of a detailed study of this system (Pascale et al 2023) in Section 5, but note here that it powers an N III] complex nearly as strong relative to the other UV lines as observed in GN-z11.…”

“…However, these clumps were typically too faint even with lensing for spectroscopic study pre-JWST, with the exception of the most massive and lowest-redshift lensed examples (e.g. Pascale et al 2023;Mestric et al 2023). JWST imaging alone has already begun revolutionizing our understanding of this area, with some of the first images revealing surprisingly dense clusters in lensed fields (e.g.…”

On the Reionization-era Globular Cluster in the Low-mass Galaxy Eridanus II

“…One obstacle to deciphering their origins is a paucity of suitable constraints on both metal-poor GCs and their host galaxies. The sensitivity and resolving power of the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST) have revealed a number of possible young clusters and/or compact star-forming clumps that may be progenitors of the GCs found in the local universe (e.g., Vanzella et al 2017Vanzella et al , 2019Vanzella et al , 2022Vanzella et al , 2023Zick et al 2020;Pascale et al 2023;Welch et al 2023). However, given the high stellar masses and star formation rates (SFRs) associated with these objects, they are likely one of the most massive and extreme examples of cluster formation in the early universe, and are unlikely to sample formation of typical metal-poor GCs.…”