Galactic Warps Through Time: Bending Disks from the Early Universe to Today

In a new study led by Vladimir Reshetnikov and collaborators, astronomers explore a peculiar and often overlooked feature of disk galaxies — vertical warps. These are gentle bends in the galactic disk that typically only appear in the outer regions. While many galaxies, including our own Milky Way, display such warps, the phenomenon has not been thoroughly studied across cosmic time. This paper seeks to fill that gap by analyzing how common and pronounced these warps were in the distant Universe.

A Look at the Galaxy Sample

To trace the history of galactic warps, the researchers gathered a sample of nearly 1,000 edge-on galaxies from two major telescope surveys: the Hubble Space Telescope’s COSMOS field and the James Webb Space Telescope’s DAWN archive. By focusing on galaxies seen from the side, they were able to directly observe vertical distortions in the disks. The team used a technique called isophote skeletonization to track the shape of each galaxy's disk and identify how much it bent from a flat, straight structure. Two specific measurements of the warp angle were used to capture these deformations: one at a fixed distance from the center, and another at the furthest point measurable in the image.

Trends in Warp Frequency

The study revealed that about 60% of the galaxies exhibited some form of disk warping, but what stood out most was how the frequency of strong S-shaped warps — those bending more than 4 degrees — changed over time. In today’s Universe (z ≈ 0), only about 10–15% of galaxies show such features. However, looking back to z ≈ 2, or roughly 10 billion years ago, that number increases to around 50%. This dramatic shift suggests that strong warps were much more prevalent in the early stages of galaxy evolution.

Why Were Warps More Common in the Past?

The authors attribute the increased warp frequency in the early Universe to the higher rate of galaxy interactions and mergers during that era. When galaxies pass close to one another or merge, gravitational forces can disturb the structure of their disks, often leading to vertical warping. These external influences are thought to play a major role in the formation of S-shaped warps. Additionally, high-redshift galaxies tend to be more gas-rich than nearby ones. Since gas responds more easily to gravitational disturbances, this could further enhance the formation of warps, especially when star formation occurs in already-distorted gas regions.

Measuring the Nature of the Warps

Beyond counting how many galaxies are warped, the researchers also studied the characteristics of the warps themselves. They observed that the average warp angle increases with redshift — a sign that warps were not just more frequent, but also potentially stronger in the past. Furthermore, they found that warps in earlier galaxies tend to begin closer to the galaxy center, suggesting a deeper influence of bending forces. Interestingly, the level of asymmetry — how different one side of the warp is from the other — remained mostly constant across time, indicating that the general shape of warps has not changed significantly.

Testing for Bias and Uncertainty

To ensure their results were not skewed by observational limitations, the team performed artificial redshifting tests, simulating what nearby galaxies would look like at higher redshifts. This helped confirm that the observed trends in warp strength and frequency were real and not artifacts of the imaging process. They also excluded smaller galaxies and those with unreliable measurements to reduce bias in their sample.

Final Thoughts and Implications

This work provides the most comprehensive look yet at the evolution of stellar disk warps across cosmic history. The clear increase in the frequency and strength of warps at higher redshifts supports the idea that galaxy interactions and gas content are crucial factors in warp formation. As galaxies evolved and settled into quieter environments, these dramatic features became less common. By studying warps, astronomers gain another tool for understanding the dynamic past of galaxies — revealing how external forces have shaped their structures over billions of years.

Source: Reshetnikov