Near-infrared and optical observations of galactic warps: A common, unexplained feature of most discs

TL;DR

This study compares near-infrared and optical observations of galactic warps in 20 edge-on galaxies, finding warps are more prominent in optical wavelengths and providing insights into warp characteristics and formation mechanisms.

Contribution

First direct comparison of NIR and optical warp properties in a statistically complete sample of edge-on galaxies, highlighting wavelength-dependent warp features.

Findings

13 of 20 galaxies are warped, more in optical than NIR

Warp transition from inner to outer disc is abrupt

S0 galaxies show minimal or no warps

Abstract

Context: Warps occurring in galactic discs have been studied extensively in HI and in the optical, but rarely in the near-infrared (NIR) bands that trace the older stellar populations. Aims: We provide NIR data of nearby edge-on galaxies, combined with optical observations, for direct comparison of the properties of galactic warps as a function of wavelength, and calculate warp curves for each galaxy and obtain the characteristic warp parameters. We discuss these properties as possible constraints to the different mechanisms that have been proposed for the development and persistence of galactic warps. Methods: We observed 20 galaxies that were selected from a statistically complete diameter-limited subsample of edge-on disc galaxies. We used the Cerro Tololo Infrared Imager (CIRIM) at the CTIO 1.5m Ritchey-Chretien telescope to acquire the NIR data. We used the 1.54m Danish and 0.92m Dutch telescopes at the European Southern Observatory's La Silla site for our optical observations. Results: Our results show that 13 of our 20 sample galaxies are warped, with the warp more pronounced in the optical than at NIR wavelengths. In the remaining seven galaxies, no warp is apparent within the limitations of our automated detection method. The transition between the unperturbed inner disc and the outer, warped region is rather abrupt. S0 galaxies exhibit very small or no warps. The magnetic model remains one of a number of interesting formation scenarios.