Evidence for a large off-centered galactic outflow and its connection to the extraplanar diffuse ionized gas in IC 1553

¹ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), Universitätsstrasse 150, 44801 Bochum, Germany
e-mail: dirks@astro.rub.de
² Ruhr University Bochum, Research Department “Plasmas with Complex Interaction”, 44801 Bochum, Germany
³ Ruhr Astroparticle and Plasma Physics Center (RAPP Center), 44780 Bochum, Germany

Received: 13 December 2022
Accepted: 1 August 2023

Abstract

Aims. We analyze a MUSE optical integral field spectrum of the star-forming edge-on galaxy IC 1553 in order to study its extraplanar diffuse ionized gas (eDIG) and the processes shaping its disk-halo interface.

Methods. We extracted the optical emission line properties from the integral field spectrum and generated the commonly used emission line diagnostic diagrams in order to analyze the ionization conditions and the distribution of the eDIG. Furthermore, we performed gravitational potential fitting to investigate the kinematics of a suspected galactic outflow.

Results. We find that the eDIG scale height has a maximum value of approximately 1.0 kpc and decreases roughly linearly with the radial distance from the galactic center in projection. The ionization state of the eDIG is not consistent with a pure photoionization scenario and instead requires a significant contribution from shock ionization. This, in addition to the gas kinematics, strongly suggests the presence of a galactic scale outflow, the origin of which lies at least 1.4 kpc away from the galactic center. The inferred shock velocity in the eDIG of approximately 225 km s⁻¹ is comparable to the escape velocity estimated from our potential modelling. The asymmetric distribution of currently star-forming clusters produces a range of different ionization conditions in the eDIG. As a result, the vertical emission line profiles vary quantitatively and qualitatively along the major axis of the galaxy. This analysis illustrates that it is crucial in studies of the eDIG to use observations that take the spatial and kinematical distributions into account, such as those done with integral field units, to form an accurate picture of the relevant physical properties.