Tracing ongoing quenching in jellyfish galaxies at z ∼ 0.35

¹ INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
² Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, 58089 Michoacán, Mexico
³ University of Nottingham School of Physics and Astronomy, University Park, Nottingham, NG7 2RD, UK
⁴ Dipartimento di Fisica e Astronomia, Université di Bologna, Via Gobetti 93/2, I-40129 Bologna, Italy
⁵ INAF, Osservatorio di Astrofisica e Scienza dello Spazio, Via Piero Gobetti 93/3, I-40129 Bologna, Italy
⁶ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
⁷ SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
⁸ Departamento de Física – CFM – Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil
⁹ Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, 10 000 Zagreb, Croatia
¹⁰ Univ. Lyon, Univ Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230 Saint-Genis-Laval, France

^⋆ Corresponding author.

Received: 31 December 2024
Accepted: 23 May 2025

Abstract

Jellyfish galaxies display long tails of gas that was removed from their stellar disks through a process known as ram-pressure stripping. These objects represent a fast transition phase between star-forming and quiescent galaxies and are often regarded as the progenitors of cluster post-starburst galaxies. We explore the evolution of these systems at 0.29<z<0.5 by identifying quenched regions in their stellar disks. To do this, we introduce a new spectral classification method based on convolutional neural networks. Signatures of ongoing quenching are detected in a relevant fraction of the stellar disk in 6 out of 18 jellyfish galaxies. When the objects with the longest tails are considered alone, however, the detection rate of quenched regions is much higher (6 out of 8 galaxies). Quenched regions are typically organized in arc-shaped regions and are concentrated at the leading edge of the disk (opposite to the tail). The global star formation rates (SFRs) of quenching jellyfish galaxies that still remain partially star-forming are systematically higher than those of other jellyfish galaxies. The SFR enhancement in jellyfish galaxies that undergo quenching is concentrated in their central regions (high stellar mass density Σ_M★), while for Σ_M★ < 10^7.5 M_⊙ kpc⁻², they follow the same Σ_M★−Σ_SFR relation as other jellyfish galaxies. Our results indicate a scenario in which gas is quickly stripped from the outskirts of the stellar disks while star formation is boosted toward the central regions of galaxies. This might lead to the outside-in quenching patterns that are observed in cluster post-starburst galaxies.