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Galactic disc warps from $z = 2.5$ to modern epoch: ruling out observational effects

Ilia V. Chugunov, Vladimir P. Reshetnikov, Alexander A. Marchuk

TL;DR

The study investigates how galactic disc warps evolve from the early universe to today by assembling a large sample of over 1000 edge-on galaxies imaged by HST and JWST and measuring warp shapes with a skeletonization method. It finds that strong S-shaped warps are much more prevalent at high redshift (about 50% near z = 2) than locally (10-15%), whereas U-shaped warps show little evolution, with the trend robust to selection effects and image quality. The results imply a physical link to the higher merger and interaction rates in the past, supporting tidal interactions as a primary mechanism for S-shaped warp formation and suggesting distinct formation channels for U-shaped warps. The work constrains warp formation theories in galaxy evolution and demonstrates the value of pushing warp studies to z less than or equal to 2.5 with HST/JWST data.

Abstract

A significant fraction of galaxies show warps in their discs, usually noticeable at its periphery. The exact origin of this phenomenon is not fully established, although multiple warp formation mechanisms are proposed. In this study, we create a sample of more than 1000 distant ($z \lesssim 2.5$) edge-on galaxies imaged by HST and JWST. For these galaxies, we measurd characteristics of warps and finally analyse how their parameters and frequency change with time. We focus on our main result that galaxies with strong warps were more prevalent in the past compared to the modern epoch. We check how selection effects and varying image quality between objects in our sample could influence our results and conclude that varying fraction of warped galaxies is not caused by observational effects, but represents a genuine evolution. Such a trend may be consistent with mergers and interactions between galaxies being the primary mechanism of warp formation, as number density of galaxies decreases with time, implying higher rate of mergers and interactions in the past.

Galactic disc warps from $z = 2.5$ to modern epoch: ruling out observational effects

TL;DR

The study investigates how galactic disc warps evolve from the early universe to today by assembling a large sample of over 1000 edge-on galaxies imaged by HST and JWST and measuring warp shapes with a skeletonization method. It finds that strong S-shaped warps are much more prevalent at high redshift (about 50% near z = 2) than locally (10-15%), whereas U-shaped warps show little evolution, with the trend robust to selection effects and image quality. The results imply a physical link to the higher merger and interaction rates in the past, supporting tidal interactions as a primary mechanism for S-shaped warp formation and suggesting distinct formation channels for U-shaped warps. The work constrains warp formation theories in galaxy evolution and demonstrates the value of pushing warp studies to z less than or equal to 2.5 with HST/JWST data.

Abstract

A significant fraction of galaxies show warps in their discs, usually noticeable at its periphery. The exact origin of this phenomenon is not fully established, although multiple warp formation mechanisms are proposed. In this study, we create a sample of more than 1000 distant () edge-on galaxies imaged by HST and JWST. For these galaxies, we measurd characteristics of warps and finally analyse how their parameters and frequency change with time. We focus on our main result that galaxies with strong warps were more prevalent in the past compared to the modern epoch. We check how selection effects and varying image quality between objects in our sample could influence our results and conclude that varying fraction of warped galaxies is not caused by observational effects, but represents a genuine evolution. Such a trend may be consistent with mergers and interactions between galaxies being the primary mechanism of warp formation, as number density of galaxies decreases with time, implying higher rate of mergers and interactions in the past.
Paper Structure (5 sections, 5 figures)

This paper contains 5 sections, 5 figures.

Table of Contents

  1. INTRODUCTION
  2. SAMPLE AND DATA ANALYSIS
  3. RESULTS
  4. VALIDATION
  5. CONCLUSIONS

Figures (5)

  • Figure 1: Distribution of galaxies by redshift (top) and the diagram showing stellar mass in solar units and redshift for galaxies in the sample (bottom).
  • Figure 2: An example showing a galaxy, its isophotes and measured centre-line (top) and the illustration of how warp angle is defined (bottom). This galaxy is located at $z = 0.20$ and has a conspicuous warp which angle is $\psi_e = 5.3^\circ$.
  • Figure 3: This diagram shows the fraction of strong S-shaped or U-shaped warps in different redshift bins. Redshift range of the bin is shown by horizontal error bars, whereas 95% confidence interval is represented by vertical ones.
  • Figure 4: An example of a galaxy artificially redshifted to different $z$. Measured warp angles and data extents are also shown.
  • Figure 5: The dependence of $\psi_e$ on $z$, stellar mass $M_*$ and data extent $d_e$ and trilinear fit to the data. Black squares with error bars represent value averaged by bins, with the parameter range of the bin being shown by horizontal error bars, and the standard deviation is represented by vertical ones.