The impact of supernovae driven winds on stream-fed protogalaxies

Abstract: SNe driven winds are widely thought to be very influential in the high-redshift Universe, shaping the properties of the circum-galactic medium, enriching the IGM with metals and driving the evolution of low-mass galaxies. However, it is not yet fully understood how SNe driven winds interact with their surroundings in a cosmological context, nor is it clear whether they are able to significantly impact the evolution of low-mass galaxies from which they originate by altering the amount of cold material these accrete from the cosmic web. We implement a standard Taylor-Sedov type solution, widely used in the community to depict the combined action of many SN explosions, in a cosmological resimulation of a low mass galaxy at z =9 from the 'Nut' suite. However, in contrast with previous work, we achieve a resolution high enough to capture individual SN remnants in the Taylor-Sedov phase, for which the solution provides an accurate description of the expansion. We report the development of a high-velocity, far-reaching galactic wind produced by the combined action of SNe in the main galaxy and its satellites, which are located in the same or a neighbouring dark matter halo. Despite this, we find that (i) this wind carries out very little mass (the measured outflow is of the order of a tenth of the inflow/star formation rate) and (ii) the cold gas inflow rate remains essentially unchanged from the run without SNe feedback. Moreover, there are epochs during which star formation is enhanced in the feedback run relative to its radiative cooling only counterpart. We attribute this 'positive' feedback to the metal enrichment that is present only in the former. We conclude that at very high redshift, efficient SNe feedback can drive large-scale galactic winds but does not prevent massive cold gas inflow from fuelling galaxies, resulting in long-lived episodes of intense star formation.(abridged)

• The paper shows that supernova-driven winds extend up to 5–6 virial radii, predominantly affecting hot and warm gas phases.
• The paper finds that dense cosmic filaments sustain cold gas inflow, ensuring continued star formation despite wind feedback.
• The paper reveals that metal enrichment from SN winds enhances cooling and star formation while distributing metals into the IGM.

Analysis of Supernovae Driven Winds in High-Redshift Protogalaxies

The paper "The impact of supernovae driven winds on stream-fed protogalaxies" provides a comprehensive investigation into the role of supernovae (SNe) driven winds in shaping the evolution of low-mass galaxies at high redshift, focusing particularly on their interaction with cold accretion streams. Utilizing cosmological hydrodynamic simulations, the study models a protogalaxy at redshift $z \geq 9$, implementing a resolution sufficiently high to capture individual SN remnants in the Taylor-Sedov expansion phase. This advancement resolves a critical limitation in previous simulations, which typically rely on subgrid wind models due to inadequate resolution.

Key Findings

1. Development of Galactic Winds: The simulations demonstrate that SNe can indeed drive a galactic wind, predominantly comprising hot ($T > 2 \times 10^5$ K) and warm ($2 \times 10^4$ K $\leq T \leq 2 \times 10^5$ K) gas phases. These winds extend to approximately 5-6 virial radii and sweep through the interstellar medium, contrasting with earlier models where winds required direct imposition.
2. Impacts on Accretion Processes: Despite the development of significant winds, the study observes that the cold gas inflow from cosmic web filaments remains largely unchanged compared to a no-feedback scenario. This suggests that the dense, filamentary structures effectively sustain gas delivery to the galaxy, shielding it from the disruptive effects of winds.
3. Star Formation and Feedback: Notably, epochs of enhanced star formation occur in simulations with SN feedback, attributed to metal enrichment which enhances cooling efficiency. This positive feedback challenges conventional views of SNe winds as solely suppressive agents in galactic evolution.
4. Winds and Metal Distribution: The wind extends metal enrichment into the intergalactic medium (IGM), potentially contributing to observed metal levels in high-redshift IGM. The simulated metallicity of the wind reaches values consistent with observations of local starburst galaxies, at roughly 0.1 to 0.5 solar metallicity.
5. Mass Loss and Efficiency: The simulated wind carries little mass, with outflow rates approximating a tenth of inflow or star formation rates. This challenges prior assumptions of efficient mass ejection and points to the need for additional mechanisms to explain observed galactic mass loss.

Implications and Future Directions

This study elucidates the complex interplay between accretion and feedback processes in early galaxy formation, suggesting that supernovae-driven winds may not significantly disrupt cold accretion flows as previously believed. Instead, the dense streams from cosmic filaments maintain their integrity, providing a steady fuel supply for star formation even in the presence of galactic winds.

The role of SN-driven winds in shaping early galaxy evolution, therefore, appears to be more nuanced, serving as a potential catalyst for metal recycling and enhancement of star formation rather than a straightforward inhibitory force. This has significant ramifications for our understanding of galaxy evolution, star formation histories, and the chemical enrichment of the universe.

Further research should explore higher mass and lower redshift environments to assess the universality of these results. Additionally, incorporating more detailed models of other feedback mechanisms, such as active galactic nuclei and cosmic ray feedback, could offer a more holistic picture of feedback-driven evolution in cosmological simulations.

Ultimately, this study is a testament to the value of high-resolution simulations in deciphering the intricacies of cosmic evolution, challenging existing paradigms, and paving the way for more accurate models of the early universe.