The Elusive Corrugations - Caught in the Dust

We report the detection of small-scale bending waves, also known as corrugations, in the dust lanes of five nearby edge-on disk galaxies. This phenomenon, where the disc mid-plane bends to become wavy, just as in warps but on a smaller scale, is seen here for the first time, in the dust lanes. We enhance the visibility of these features using unsharp masking, trace the dust mid-plane across the disc, measure the corrugation amplitude by eye and the corrugation wavelength using Fourier analysis. The corrugation amplitude is found to be in the range of 70–300pc and the wavelengths lie between 1 and 5 kpc. The fact that corrugations are seen in stars, gas (Milky Way, IC 2233 etc) and dust indicate gravitational instability as the likely origin. Corrugations can be, in fact as common as warps but may go undetected because of their small size. We assemble mounting evidence indicating that corrugations in the outskirts of gaseous disks may lead to 'silent' star formation.