Letter to the Editor

Ubiquitous broad-line emission and the relation between ionized gas outflows and Lyman continuum escape in Green Pea galaxies

¹ ARAID Foundation, Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Unidad Asociada al CSIC, Plaza San Juan 1, 44001 Teruel, Spain
e-mail: ramorin@cefca.es
² Departamento de Astronomía, Universidad de La Serena, Avda. Juan Cisternas 1200, La Serena, Chile
³ Gemini Observatory, 670 N. A’ohoku Place, Hilo, HI 96720, USA
⁴ University of Michigan, Department of Astronomy, 323 West Hall, 1085 S. University Ave, Ann Arbor, MI 48109, USA
⁵ Instituto de Investigación Multidisciplinar de Investigación y Posgrado, Universidad de La Serena, Raúl Bitrán 1305, La Serena, Chile
⁶ Instituto de Astrofísica de Andalucía, CSIC, Apartado de correos 3004, 18080 Granada, Spain
⁷ Department of Astronomy, University of Geneva, 51 Chemin Pegasi, 1290 Versoix, Switzerland
⁸ Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, 14-b Metrolohichna str., Kyiv 03143, Ukraine
⁹ Gemini Observatory/NSF’s NOIRLab, Casilla 603, La Serena, Chile
¹⁰ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
¹¹ Center for Cosmology and Computational Astrophysics, Institute for Advanced Study in Physics, Zhejiang University, Hangzhou 310058, PR China
¹² Institute of Astronomy, School of Physics, Zhejiang University, Hangzhou 310058, PR China
¹³ Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USA
¹⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁵ Department of Astronomy, Oskar Klein Centre, Stockholm University, 106 91 Stockholm, Sweden
¹⁶ Center for Astrophysical Sciences, Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
¹⁷ Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA
¹⁸ INAF – Osservatorio Astronomico di Roma, Via di Frascati 33, 00078 Monte Porzio Catone, Italy
¹⁹ Astronomy Department, University of Virginia, PO Box 400325 Charlottesville, VA 22904-4325, USA
²⁰ Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
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 Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
²⁵ Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern University, Evanston, IL 60201, USA

Received: 8 January 2024
Accepted: 5 February 2024

Abstract

We report observational evidence of highly turbulent ionized gas kinematics in a sample of 20 Lyman continuum (LyC) emitters (LCEs) at low redshift (z ∼ 0.3). Detailed Gaussian modeling of optical emission line profiles in high-dispersion spectra consistently shows that both bright recombination and collisionally excited lines can be fitted as one or two narrow components with intrinsic velocity dispersion of σ ∼ 40 − 100 km s⁻¹, in addition to a broader component with σ ∼ 100 − 300 km s⁻¹, which contributes up to ∼40% of the total flux and is preferentially blueshifted from the systemic velocity. We interpret the narrow emission as highly ionized gas close to the young massive star clusters and the broader emission as a signpost of unresolved ionized outflows, resulting from massive stars and supernova feedback. We find a significant correlation between the width of the broad emission and the LyC escape fraction, with strong LCEs exhibiting more complex and broader line profiles than galaxies with weaker or undetected LyC emission. We provide new observational evidence supporting predictions from models and simulations; our findings suggest that gas turbulence and outflows resulting from strong radiative and mechanical feedback play a key role in clearing channels through which LyC photons escape from galaxies. We propose that the detection of blueshifted broad emission in the nebular lines of compact extreme emission-line galaxies can provide a new indirect diagnostic of Lyman photon escape, which could be useful to identify potential LyC leakers in the epoch of reionization with the JWST.