Warped Disk Galaxies. II. From the Cosmic Web to the Galactic Warp

TL;DR

This paper tests whether galactic warps are connected to the cosmic web by using a large SDSS-derived sample of warped disk galaxies and a carefully matched unwarped control. By analyzing the spatial distribution of satellites as a proxy for underlying dark matter halo shapes, and examining the proximity and orientation of filaments identified with DisPerSE, the study finds that warped hosts exhibit more satellites, lower satellite-to-central mass ratios, and pronounced anisotropy in satellite positions, with S-type warps aligning with nearby filaments and U-type warps preferring perpendicular orientations. The incidence of warps increases closer to filaments, and the satellite–filament alignment differs by warp morphology, suggesting that filamentary accretion and halo torques regulate warp formation. These results provide observational evidence linking the cosmic web to halo structure and disk warps, implying a coherent framework for warp formation that depends on the evolutionary stage of the halo–filament system and motivating future kinematic studies and simulations to flesh out the halo–web–disk coevolution.

Abstract

Galactic warps are common in disk galaxies. While often attributed to galaxy--galaxy tides, a non-spherical dark matter (DM) halo has also been proposed as a driver of disk warping. We investigate links among warp morphology, satellite distribution, and large-scale structure using the Sloan Digital Sky Survey catalog of warped disks compiled by Zee et al.\ (2022). Warps are classified into 244 S and 127 U types, hosting 1,373 and 740 satellites, respectively, and are compared to an unwarped control matched in stellar mass, redshift, and local density. As an indirect, population-level proxy for the host halo's shape and orientation, we analyze the stacked spatial distribution of satellites. Warped hosts show a significant anisotropy: an excess at $45^{\circ}<φ<90^{\circ}$ (measured from the host major axis), peaking at $P(φ)\simeq 0.003$, versus nearly isotropic controls. Satellites of S-type warps preferentially align with the nearest cosmic filament, whereas those of U-type warps are more often perpendicular. The incidence of warps increases toward filaments ($r_{\rm fil}<4,{\rm Mpc},h^{-1}$), while the number of satellites around warped hosts remains approximately constant with filament distance, indicating a direct influence of the large-scale environment. We discuss possible links between galactic warps and the cosmic web, including anisotropic tidal fields and differences in evolutionary stage.

Figures (8)

• Figure 1: Left: The normalized histogram of the number of satellites per central galaxy for the unwarped control sample (dashed black), S type (red), and U type warped galaxies (blue). The mean satellite count for each category is described by triangle symbols, showing that warped galaxies systematically host more satellites than their unwarped counterparts. Middle: The distribution of satellite-to-central stellar mass ratios for the same three groups. The mean mass ratio is displayed as triangle symbols, revealing that warped galaxies tend to host lower-mass satellites on average. Right: The radial number density of satellites as a function of projected separation ($r_{\rm p}$) from the central galaxy, for unwarped control galaxies (dashed black), S type (red), and U type (blue) warped galaxies. Shaded region represents Poisson errors for each bin.
• Figure 2: Upper: Density distribution of stacked satellite galaxies in $\Delta x$–$\Delta y$ space relative to their central galaxies for the unwarped control sample (left), S-type warped galaxies (middle), and the residual map obtained by subtracting the control sample from the S-type distribution (right). White contours are drawn at 0.5$\sigma$ intervals. An equal number of all stacked satellites, randomly selected from the control sample, is used as indicated. Larger and smaller black arrows mark the directions of the stronger and weaker warp sides, respectively. Lower: Same as the upper panels, but for U-type warped galaxies.
• Figure 3: Same as Figure \ref{['fig:2']}, but for central galaxies that host at least six satellites ($N_\textrm{Sat}\ge 6$).
• Figure 4: Upper: Probability density function, $P(\phi)$, of satellite position angle, $\phi$, relative to the major axis of the central galaxy, for unwarped control sample (left, black), S type (middle, red), and U type (right, blue) warped galaxies. Shaded region represents Poisson errors for each bin. For comparison, the expected isotropic distribution with the same number of central and satellite galaxies is shown as a gray horizontal line, while the 3$\sigma$ range of its random distribution is shaded in gray. For S and U type warped galaxies, significant anisotropies appear, with satellites preferentially clustering at $45^{\circ} < \phi < 90^{\circ}$. Lower: Same as the upper panels, but for central galaxies that host at least six satellites ($N_\textrm{Sat}\ge 6$).
• Figure 5: Left: The normalized histogram of the distance to the nearest filament, $r_\textrm{Fila}$, for the unwarped control sample (dashed black), S type (red), and U type warped galaxies (blue). Middle: Fraction of warped galaxies of S type (red) and U type (blue) as a function of $D_\textrm{Fila}$. Shaded region represents Poisson errors in each $r_\textrm{Fila}$ bin. Right: Same as the middle panel, but for strongly warped galaxies ($\alpha \geq 4.9^\circ$).