Large Scale Compressible Turbulence in the Interstellar Medium of CSWA13, a Star-Forming Lensed Galaxy at z = 1.87

Core Concepts

Analysis of the velocity fields of CSWA13, a star-forming galaxy at z=1.87, reveals evidence of large-scale supersonic compressible turbulence in the interstellar medium, suggesting its origin predates the formation of young stars and wind outflows, potentially stemming from a merger or tidal event.

Abstract

Bibliographic Information:

Goldman, I. (2024). Evidence for large scale compressible turbulence in the ism of CSWA13, a star-Forming Lensed Galaxy at z = 1.87 with outflowing wind. arXiv preprint arXiv:2406.08578v2.

Research Objective:

This study investigates the presence and nature of turbulence in the interstellar medium (ISM) of CSWA13, a gravitationally lensed star-forming galaxy at a redshift z=1.87, by analyzing the spatially resolved velocity fields of its nebular gas and wind outflow.

Methodology:

The authors digitized velocity curves of the nebular gas and wind outflow from previous observations of CSWA13. They then derived and analyzed the autocorrelation functions and structure functions of the residual velocity fields along the galaxy's major axis to characterize the turbulence.

Key Findings:

• The structure functions of both the nebular gas and wind velocity fields exhibit a logarithmic slope of 1 on large spatial scales and 2 on small spatial scales, consistent with supersonic compressible turbulence characterized by a one-dimensional power spectrum ∝ k−2.
• The autocorrelation functions reveal correlations over scales comparable to the size of the galaxy's major axis, indicating the large-scale nature of the turbulence.
• The estimated turbulent timescale (approximately 200 Myr) suggests that the turbulence predates the formation of young stars and the wind outflow in CSWA13.
• Analysis of the structure functions provides an estimated effective depth of the turbulent layer, approximately 2 kpc.

Main Conclusions:

The study concludes that the observed velocity fields in CSWA13 are best explained by the presence of large-scale supersonic compressible turbulence in its ISM. This turbulence likely originated from a large-scale event, such as a merger or tidal interaction, which predates the formation of young stars and their associated wind outflows.

Significance:

This research provides valuable insights into the dynamics of the ISM in high-redshift galaxies and the role of turbulence in galaxy evolution. The findings suggest that large-scale events like mergers can drive turbulence, which may influence subsequent star formation and wind outflows.

Limitations and Future Research:

The study relies on the analysis of velocity fields along a single axis (the galaxy's major axis). Future research with three-dimensional velocity data would provide a more comprehensive understanding of the turbulence. Further investigations into the properties of similar high-redshift galaxies could help confirm the prevalence and implications of large-scale compressible turbulence in the early universe.

Stats

The turbulent timescale corresponding to the largest scale is about 200 Myr.
The estimated age of the wind and of the young stars is an order of magnitude smaller than the turbulent timescale.
The effective depth of the turbulent layer is ∼2kpc.

Quotes

Key Insights Distilled From

Evidence for large scale compressible turbulence in the ism of CSWA13, a star-Forming Lensed Galaxy at z = 1.87 with outflowing wind

by Itzhak Goldm... at arxiv.org 11-06-2024

https://arxiv.org/pdf/2406.08578.pdf

Deeper Inquiries

How might the presence of large-scale compressible turbulence in the early universe impact the formation and evolution of galaxies other than CSWA13?

Large-scale compressible turbulence in the early universe could have significantly impacted the formation and evolution of galaxies in several ways:

Regulation of Star Formation: Turbulence, especially on large scales, can act as a regulating mechanism for star formation. The turbulent energy cascade can create local regions of high density, promoting gravitational collapse and star formation. Conversely, turbulence can also disperse dense gas, effectively suppressing star formation. This dual role makes turbulence a crucial factor in shaping the star formation history of galaxies.
Galaxy Morphology: The turbulent energy cascade can influence the morphology of galaxies. Large-scale turbulence can disrupt the formation of well-defined disks, leading to more irregular or clumpy structures. This is particularly relevant for high-redshift galaxies, which are observed to be more irregular than their local counterparts.
Metal Enrichment and Feedback: Turbulence can drive the mixing of metals produced in supernova explosions throughout the interstellar medium (ISM). This metal enrichment is essential for the formation of subsequent generations of stars and planets. Furthermore, turbulence can facilitate the transport of energy and momentum from supernovae and stellar winds, influencing the dynamics of the ISM and regulating further star formation.
Galaxy Mergers and Interactions: As galaxies merge and interact, large-scale turbulence can be generated by the violent gravitational forces involved. This turbulence can trigger starbursts, drive gas outflows, and reshape the merging galaxies, ultimately influencing their final morphology and star formation properties.
Observing the characteristics of turbulence in high-redshift galaxies like CSWA13 provides valuable insights into the complex interplay between these processes in the early universe.

Could other phenomena, such as supernova explosions or active galactic nuclei, contribute to the observed turbulence in CSWA13, or is a merger or tidal event the most plausible explanation?

While the study strongly suggests a merger or tidal event as the most plausible explanation for the large-scale compressible turbulence observed in CSWA13, other phenomena could contribute to the overall turbulent energy budget within the galaxy:

Supernova Explosions: Supernovae inject a tremendous amount of energy into the ISM, driving powerful shock waves that can generate turbulence. However, the spatial scales associated with individual supernova remnants are typically smaller than the large-scale turbulence observed in CSWA13. It's possible that multiple supernovae clustered in space and time could contribute to larger-scale turbulence, but this scenario might not be as likely as a single, more energetic event like a merger.
Active Galactic Nuclei (AGN): AGN, powered by accretion onto supermassive black holes, can launch powerful jets and outflows that interact with the surrounding ISM. These interactions can drive shocks and turbulence on various scales. However, there's no direct evidence of AGN activity in CSWA13.
The study emphasizes the long timescale of the observed turbulence (∼200 Myr) as a key factor supporting the merger/tidal event hypothesis. This timescale is significantly longer than the typical lifetimes of individual supernova remnants or even the active phases of some AGN. A merger or tidal event, on the other hand, can inject energy on much longer timescales, potentially explaining the observed turbulence in CSWA13.

If turbulence is a common feature of high-redshift galaxies, what are the implications for our understanding of the processes that govern the formation of stars and galaxies in the early universe?

If large-scale turbulence is confirmed as a common feature of high-redshift galaxies, it would have profound implications for our understanding of the early universe:

Revised Galaxy Formation Models: Current galaxy formation models would need to incorporate the significant impact of turbulence on the dynamics of gas, star formation, and feedback mechanisms. This would require more sophisticated simulations and a deeper understanding of turbulence on galactic scales.
Early Enrichment and Chemical Evolution: The efficient mixing of metals by turbulence in the early universe could explain the observed metallicity of early stars and galaxies. This has implications for understanding the timescales of chemical enrichment and the formation of the first metal-rich objects.
Impact on the Intergalactic Medium: Turbulent outflows driven by supernovae and stellar winds, potentially enhanced by large-scale turbulence, could have enriched the intergalactic medium with metals and influenced its thermal and ionization states. This has consequences for the formation of subsequent generations of galaxies and the overall evolution of the universe.
Observing and characterizing turbulence in high-redshift galaxies is crucial for refining our understanding of the complex processes that governed the formation and evolution of galaxies in the early universe. The study of CSWA13 provides a compelling example of how turbulence can shape the properties of individual galaxies and offers a glimpse into the turbulent nature of the early universe.