Linking Mg II and [O II] spatial distribution to ionizing photon escape in confirmed LyC leakers and non-leakers^⋆,⋆⋆

¹ Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USA
e-mail: floriane.leclercq@austin.utexas.edu
² Astronomy Department, Williams College, Williamstown, MA 01267, USA
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
⁵ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
⁶ Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, 14-b Metrolohichna Str., Kyiv 03143 } Ukraine
⁷ Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064, USA
⁸ Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁹ Instituto de Investigación Multidisciplinar en Ciencia y Tecnología, Departamento de Física y Astronomía, Universidad de La Serena, Avda. Juan Cisternas 1200, La Serena, Chile
¹⁰ Institut d’Astrophysique de Paris, CNRS UMR7095, Sorbonne Université, 98bis Boulevard Arago, 75014 Paris, France
¹¹ CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Univ. Lyon, Univ. Lyon1, Ens de Lyon, 69230 Saint-Genis-Laval, France
¹² Center for Cosmology and Computational Astrophysics, Institute for Advanced Study in Physics, Zhejiang University, Hangzhou 310058, PR China
¹³ Institute of Astronomy, School of Physics, Zhejiang University, Hangzhou 310058, PR China
¹⁴ Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA
¹⁵ Department of Physics and Astronomy, Johns Hopkins University, School of Earth and Space Exploration, Arizona State University, Baltimore, MD 21218, USA
¹⁶ Astronomy Department, University of Michigan, Ann Arbor, MI 48103, USA
¹⁷ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
¹⁸ Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, 316 Church St. SE, Minneapolis, MN 55455, USA
¹⁹ Astronomy Department, University of Virginia, PO Box 400325 Charlottesville, VA 22904-4325, USA
²⁰ Institut fur Physik und Astronomie, Universitat Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
²¹ Department of Astronomy & Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
²² Institute for Computational & Data Sciences, The Pennsylvania State University, University Park, PA 16802, USA
²³ Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA
²⁴ Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
²⁵ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 1800 Sherman Avenue, Evanston, IL 60201, USA

Received: 26 January 2024
Accepted: 13 March 2024

Abstract

The geometry of the neutral gas in and around galaxies is a key regulator of the escape of ionizing photons. We present the first statistical study aimed at linking the neutral and ionized gas distributions to the Lyman continuum (LyC) escape fraction (f_esc^LyC) in a sample of 22 confirmed LyC leakers and non-leakers at z ≈ 0.35 using the Keck Cosmic Web Imager (Keck/KCWI) and the Low Resolution Spectrograph 2 (HET/LRS2). Our integral field unit data enable the detection of neutral and low-ionization gas, as traced by Mg II, and ionized gas, as traced by [O II], extending beyond the stellar continuum for seven and ten objects, respectively. All but one object with extended Mg II emission also show extended [O II] emission; in this case, Mg II emission is always more extended than [O II] by a factor 1.2 on average. Most of the galaxies with extended emission are non or weak LyC leakers (f_esc^LyC < 5%), but we find a large diversity of neutral and low-ionization gas configurations around these weakly LyC-emitting galaxies. Conversely, the strongest leakers (f_esc^LyC > 5%) appear uniformly compact in both Mg II and [O II] with exponential scale lengths ≲1 kpc. Most are unresolved at the resolution of our data. We also find a trend between f_esc^LyC and the spatial offsets of the nebular gas and the stellar continuum emission. Moreover, we find significant anticorrelations between the spatial extent of the neutral and/or low-ionization gas and the [O III]/[O II] ratio, and Hβ equivalent width, as well as positive correlations with metallicity and UV size, suggesting that galaxies with more compact neutral and/or low-ionization gas sizes are more highly ionized. The observations suggest that strong LyC emitters do not have extended neutral and/or low-ionization gas halos and ionizing photons may be emitted in many directions. Combined with high ionization diagnostics, we propose that the Mg II, and potentially [O II], spatial compactness are indirect indicators of LyC emitting galaxies at high redshift.