The Sunburst Arc with JWST. IV. The importance of interaction, turbulence, and feedback for Lyman-continuum escape

TL;DR

This study uses JWST/NIRSpec IFU observations of the gravitationally lensed Sunburst Arc (z≈2.37) to map rest-frame optical ISM properties across multiple lensed images. Through CubeFitter.jl–driven line fitting and uncertainty corrections, the authors produce high-resolution maps of kinematics, dust, ionization, and abundances, and construct a magnification-weighted global spectrum for direct comparison to unlensed Lyman-Continuum emitters. They find a rotating but turbulence-dominated ISM, with a highly ionized LCE cluster and little mechanical feedback around the escape region, supporting a LyC escape scenario in which tidal stripping exposes a thin HI envelope that is readily ionized by the cluster. The results imply that photoionization, aided by interaction-driven gas removal, creates escape paths without requiring large-scale feedback, and demonstrate JWST’s capability to reveal the microphysics of LyC leakage in distant galaxies.

Abstract

At present, the best opportunity for detailed Lyman Continuum escape studies is in gravitationally lensed galaxies at z >~ 2. Only one such galaxy currently exists in the literature with sufficient spatial magnification: The Sunburst Arc at redshift z = 2.37. Here, we present rest-frame optical JWST NIRSpec integral field observations of the Sunburst Arc that cover a large fraction of the source plane. From this dataset, we generate precise maps of ISM kinematics, dust geometry, ionization, and chemical enrichment. We extract a stacked spectrum of five gravitationally lensed images of the Lyman-Continuum leaking cluster, as well as an magnification-corrected, integrated spectrum of most of the galaxy, enabling a direct comparison to other LyC leakers in the literature. We find that the galaxy rotates but also shows strong, possibly dominant, signatures of turbulence, which are indicative of recent or ongoing major interaction. The cluster that leaks ionizing photons shows little variation in kinematics or dust coverage, but dramatically elevated ionization, indicating that photoionization is the predominant mechanism that creates paths for LyC escape. We conjecture that tidal stripping of H I gas due to an interaction could have removed a large portion of the neutral ISM around the LyC emitting cluster, making it easier for the cluster to completely ionize the rest.

Figures (16)

• Figure 1: Left: NIRCam color composite of the N and NW segments of the Sunburst Arc and member galaxies of the lensing foreground cluster. The approximate footprints of NIRSpec IFU pointings are overlaid in cyan (P1), magenta (P2), and yellow (P3). The RGB channels show the rest-frame near-IR in the NIRCam filter F444W, rest-frame green in F200W, and rest-frame blue/optical in F115W, respectively. The image is oriented with N up, E to the left. Right: Median NIRSpec IFU cube of P1 (upper) and P2+P3 (lower). Six lensed images of the LCE cluster plus the object "Godzilla" diego2022choe2025 are marked. All three panels are shown using square root -stretched color scales, to strike a balance between bright and faint features.
• Figure 2: An artist's impression approximate view of the de-lensed source galaxy, with the approximate de-lensed footprints of the three IFU pointings overlaid along with an approximate physical scale bar. While the upper, diffuse areas are ray traced from image plane to source plane, the approximate position, color and brightness of the observed clumps/clusters seen in the bottom parts are added by hand. The arrow points to the LCE cluster. Adapted from sharon2022.
• Figure 3: Restframe blue/optical spectrum of the LCE cluster in the Sunburst Arc. The upper panel shows the flux on a log $y$-axis to display features on a wide range of scales, while the lower panel shows continuum and uncertainty spectrum on a linear scale.
• Figure 4: Mask used for kinematic measurements. The median map of P1 is shown in grayscale. Overlaid is the the inverse magnification map of sharon2022, with higher values meaning that a spaxel is weighted more when deriving global properties of the galaxy. Spaxels in pure grayscale are not included in these derivations. Also shown are the $\mu=100$ contours from the lensing model of sharon2022.
• Figure 5: Maps of line emission within Pointing 1, based on single-component Gaussian profile fits for each individual spaxel. Fluxes are given in ergs/(s cm2) except stellar continuum which is given in MJy/SR. Stellar continuum is also shown as contours in the line maps to show the relative position of line emission features. The line maps are showed on a logarithmic color scale to better present extended, low surface brightness structure. The hand drawn masks of Sect. \ref{['sec:masking']} are applied. The four bright spots in the center of the Ne3 map are an artifact.