A ring-shaped starburst as a galactic wind-generating mechanism: Morphology, emission, and mass ejection

TL;DR

This paper investigates how ring-shaped nuclear starbursts influence galactic winds in NGC 253 by performing axisymmetric hydrodynamic simulations with the AMRVAC code, injecting winds from a central RSS at various heights. It demonstrates that RSSs yield a more complex, collimated wind structure with multi-phase gas and H$\alpha$ filaments, and that even modest vertical offsets create pronounced north–south asymmetries in morphology and mass flux. Through synthetic H$\alpha$ and X-ray maps and a mass-flux analysis, the work identifies conditions that best reproduce observed features, notably a ~100 pc offset and ~2.3 Myr age, while highlighting strong, short-lived mass-loading differences between hemispheres. These findings underscore the importance of starburst geometry and radiative cooling in shaping galactic winds and offer a framework for interpreting winds in ring-starburst galaxies such as NGC 253, with a path forward to fully 3D modeling and inclusion of additional physics.

Abstract

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. 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 analyze the asymmetry of the outflows due to the bursts 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. We used the hydrodynamic code AMRVAC to simulate galactic wind ejection coming from a central ring-like starburst located at different vertical positions. 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 H alpha 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.

Figures (14)

• Figure 1: Mass loss (left side) and mechanical luminosity (right side) for an instantaneous burst (blue) and a continuous one (orange) obtained with SB99.
• Figure 2: Set up for a ring-like starburst on an axisymmetric simulation, with a radius of injection equal to the internal radius of the torus, $R_i$, and positioned at a distance from the symmetry axes equal to the external radius of the torus: $R_e$ minus $R_i$.
• Figure 3: Simulation for a central and continuous starburst (MCENc) at t= 4 Myr; the left side shows density and the right side shows H$\alpha$(orange) and X-rays (blue) emissions.
• Figure 4: Gas density maps for the 0.1 kpc off-centre continuous model (MOC100c) going from a time of 2 Myr on the top to 4 Myr on the bottom.
• Figure 5: H$\alpha$ and X-ray emission maps of the wind simulated for the off-centre continuous starburst model (MOC100c), shifted by 0.1 kpc, at t=$4$ Myr.