A ∼15 kpc outflow cone piercing through the halo of the blue compact metal-poor galaxy SBS 0335–052E^⋆

¹ European Southern Observatory, Av. Alonso de Córdova 3107, 763 0355 Vitacura, Santiago, Chile
e-mail: eherenz@eso.org
² Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
³ Department of Physics & Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN, 55105 USA
⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternware 16, 14482 Potsdam, Germany
⁵ Pontificia Universidad Católica de Chile – Instituto de Astrofísica, Av. Vicuña Mackenna 4860, 897 0117 Macul, Santiago, Chile
⁶ Department of Astronomy, Stockholm University, AlbaNova University Centre, 106 91 Stockholm, Sweden
⁷ Instituto de Astrofísica e Ciências do Espaço – Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
⁸ Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
⁹ Universität Bonn, Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany

Received: 9 September 2022
Accepted: 5 December 2022

Abstract

Context. Outflows from low-mass star-forming galaxies are a fundamental ingredient for models of galaxy evolution and cosmology. Despite seemingly favourable conditions for outflow formation in compact starbursting galaxies, convincing observational evidence for kiloparsec-scale outflows in such systems is scarce.

Aims. The onset of kiloparsec-scale ionised filaments in the halo of the metal-poor compact dwarf SBS 0335−052E was previously not linked to an outflow. In this paper we investigate whether these filaments provide evidence for an outflow.

Methods. We obtained new VLT/MUSE WFM and deep NRAO/VLA B-configuration 21 cm data of the galaxy. The MUSE data provide morphology, kinematics, and emission line ratios of Hβ/Hα and [O III]λ5007/Hα of the low surface-brightness filaments, while the VLA data deliver morphology and kinematics of the neutral gas in and around the system. Both datasets are used in concert for comparisons between the ionised and the neutral phase.

Results. We report the prolongation of a lacy filamentary ionised structure up to a projected distance of 16 kpc at SB_Hα = 1.5 × 10⁻¹⁸ erg s cm⁻² arcsec⁻². The filaments exhibit unusual low Hα/Hβ ≈ 2.4 and low [O III]/Hα ∼ 0.4 − 0.6 typical of diffuse ionised gas. They are spectrally narrow (∼20 km s⁻¹) and exhibit no velocity sub-structure. The filaments extend outwards from the elongated H I halo. On small scales, the N_HI peak is offset from the main star-forming sites. The morphology and kinematics of H I and H II reveal how star-formation-driven feedback interacts differently with the ionised and the neutral phase.

Conclusions. We reason that the filaments are a large-scale manifestation of star-formation- driven feedback, namely limb-brightened edges of a giant outflow cone that protrudes through the halo of this gas-rich system. A simple toy model of such a conical structure is found to be commensurable with the observations.