DIRBE EVIDENCE FOR A WARP IN THE INTERSTELLAR DUST LAYER AND STELLAR DISK OF THE GALAXY

The Diffuse Infrared Background Experiment (DIRBE) of the Cosmic Background Explorer (COBE) has mapped the surface brightness distributions of the Galactic plane at wavelengths from 1.25 to 240 mum. In these maps the latitude of peak brightness, as a function of longitude, traces a roughly sinusoidal curve of period approximately 360-degrees. In the far-infrared, where emission by interstellar dust dominates the surface brightness, this curve agrees well with that derived from maps of the velocity-integrated H I, suggesting that the layers of dust and neutral atomic hydrogen are similarly displaced from the Galactic plane. In the near-infrared (lambda < 5 mum), where old disk stars dominate the emission, the brightness crest exhibits the same phase but roughly half the amplitude. The reduced amplitude of the warp in stellar light could result from a lesser warping of the stellar disk, or from a more rapid falloff of the density of stars relative to the density of gas, possibly due to a radial truncation of the disk.