Connecting Lyman-$\alpha$ and ionizing photon escape in the Sunburst Arc

M. Riley Owens; Keunho J. Kim; Matthew B. Bayliss; T. Emil Rivera-Thorsen; Keren Sharon; Jane R. Rigby; Alexander Navarre; Michael Florian; Michael D. Gladders; Jessica G. Burns; Gourav Khullar; John Chisholm; Guillaume Mahler; Hakon Dahle; Christopher M. Malhas; Brian Welch; Taylor A. Hutchison; Raven Gassis; Suhyeon Choe; Prasanna Adhikari

arXiv · 2410.03660

Connecting Lyman-$\alpha$ and ionizing photon escape in the Sunburst Arc

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Abstract

We investigate the Lyman-$\alpha$ (Ly$\alpha$) and Lyman continuum (LyC) properties of the Sunburst Arc, a $z=2.37$ gravitationally lensed galaxy with a multiply-imaged, compact region leaking LyC and a triple-peaked Ly$\alpha$ profile indicating direct Ly$\alpha$ escape. Non-LyC-leaking regions show a redshifted Ly$\alpha$ peak, a redshifted and central Ly$\alpha$ peak, or a triple-peaked Ly$\alpha$ profile. We measure the properties of the Ly$\alpha$ profile from different regions of the galaxy using $R\sim5000$ Magellan/MagE spectra. We compare the Ly$\alpha$ spectral properties to LyC and narrowband Ly$\alpha$ maps from Hubble Space Telescope (HST) imaging to explore the subgalactic Ly$\alpha-$LyC connection. We find strong correlations (Pearson correlation coefficient $r>0.6$) between the LyC escape fraction ($f_{\rm esc}^{\rm LyC}$) and Ly$\alpha$ (1) peak separation $v_{\rm{sep}}$, (2) ratio of the minimum flux density between the redshifted and blueshifted Ly$\alpha$ peaks to continuum flux density $f_{\rm{min}}/f_{\rm{cont}}$, and (3) equivalent width. We favor a complex \ion{H}{1} geometry to explain the Ly$\alpha$ profiles from non-LyC-leaking regions and suggest two \ion{H}{1} geometries that could diffuse and/or rescatter the central Ly$\alpha$ peak from the LyC-leaking region into our sightline across transverse distances of several hundred parsecs. Our results emphasize the complexity of Ly$\alpha$ radiative transfer and its sensitivity to the anisotropies of \ion{H}{1} gas on subgalactic scales. Large differences in the physical scales on which we observe spatially variable direct escape Ly$\alpha$, blueshifted Ly$\alpha$, and escaping LyC photons in the Sunburst Arc underscore the importance of resolving the physical scales that govern Ly$\alpha$ and LyC escape.

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M. Riley Owens, Keunho J. Kim, Matthew B. Bayliss, T. Emil Rivera-Thorsen, Keren Sharon, Jane R. Rigby, Alexander Navarre, Michael Florian, Michael D. Gladders, Jessica G. Burns, Gourav Khullar, John Chisholm, Guillaume Mahler, Hakon Dahle, Christopher M. Malhas, Brian Welch, Taylor A. Hutchison, Raven Gassis, Suhyeon Choe, Prasanna Adhikari. 2024-10-04. Connecting Lyman-$\alpha$ and ionizing photon escape in the Sunburst Arc. https://arxiv.org/abs/2410.03660

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