A ring-shaped starburst as a galactic wind-generating mechanism

Context. Star formation bursts promote the ejection of material from the hosting galaxies due to the momentum and energy injected by winds from massive stars and supernova explosions. Numerical or analytical models generally consider that the mass, momentum, and energy injections result from bursts in a nuclear star formation region. However, star formation bursts have recently been observed in ring-like regions in the nuclear part of the galaxies. One example is NGC 253, which has shown a central toroidal burst and an asymmetric galactic wind observed in thermal X-ray emission. Aims. The general aim of this work is to study the effect of mechanical energy injection from stellar winds and supernova explosions in star-forming bursts distributed in rings around the nucleus of the galaxy NGC 253. Additionally, these partial objectives allow us to analyse the asymmetry of the outflows due to the burst’s position as well as to study the formation of filaments with optical emission and make comparisons with recent observations of galaxies with these types of star-forming bursts. Methods. We used the hydrodynamic code AMRVAC to simulate galactic wind ejection coming from a central ring-like starburst located at different vertical positions: at the centre and in 10 pc and 0.1 kpc from the centre. Our models considered the starburst evolution following the stellar population of an instantaneous and continuous burst, using the SB99 synthesis models, where the mechanical energy injected via SN and stellar wind are considered. To compare our results with the X-ray emission from the outflow from NGC253, we built the Hα and X-ray emissions maps and quantified the mass flux of the galactic wind. Results. We showed that including a ring-shaped starburst (RSS) generates a more complex structured wind than what would be expected for a spherical starburst injection. Besides the interaction between the wind generated by the RSS and the host galaxy, it can generate dense filamentary structures with Hα emission. The mass flux analysis of our models shows that the variation in the vertical position of the starburst can generate a variation in the mass flux of each lobe of the wind up to an order of magnitude. However, this difference is sustained only for a short period, with the flux tending to be symmetrical once it enters into a free-wind solution. Conclusions. The inclusion of RSS in our simulations generates a wind with a more defined structure, with a more collimated cone of injection. This allows it to break through the thick disk and generate a double flow galactic wind with an off-centre starburst, resulting in expected structures such as Hα filaments. Through the change in the vertical position of the starburst about the host galaxy, our simulations were able to generate an asymmetric wind, revealing important differences in terms of size and mass flux. On the gas multi-phase structure of each side of the wind, the level of variation is in direct correlation with the variation in position, offering a plausible explanation for the kind of winds observed on NGC 253.