Super star cluster feedback driving ionization, shocks and outflows in the halo of the nearby starburst ESO 338-IG04

Abstract

Context. Stellar feedback strongly affects the interstellar medium (ISM) of galaxies. Stellar feedback in the first galaxies likely plays a major role in enabling the escape of LyC photons, which contribute to the re-ionization of the Universe. Nearby starburst galaxies serve as local analogues allowing for a spatially resolved assessment of the feedback processes in these galaxies. Aims.We aim to characterize the feedback effects from the star clusters in the local high-redshift analogue ESO 338-IG04 on the ISM and compare the results with the properties of the most massive clusters. Methods. We used high quality VLT/MUSE optical integral field data to derive the physical properties of the ISM such as ionization, density, shocks, and performed new fitting of the spectral energy distributions of the brightest clusters in ESO 338-IG04 from HST imaging. Results.We find that ESO 338-IG04 has a large ionized halo which we detect to a distance of 9 kpc. We identify four Wolf-Rayet (WR) clusters based on the blue and red WR bump. We follow previously identified ionization cones and find that the ionization of the halo increases with distance. Analysis of the galaxy kinematics shows two complex outflows driven by the numerous young clusters in the galaxy. We find a ring of shocked emission traced by an enhanced [O I]/Hα ratio surrounding the starburst and at the end of the outflow. Finally we detect nitrogen enriched gas associated with the outflow, likely caused by the WR stars in the massive star clusters. Conclusions. Photoionization dominates the central starburst and sets the ionization structure of the entire halo, resulting in a density bounded halo, facilitating the escape of LyC photons. Outside the central starburst, shocks triggered by an expanding super bubble become important. The shocks at the end of the outflow suggest interaction between the hot outflowing material and the more quiescent halo gas.