First All-Sky maps of the ROSAT Soft X-ray Diffuse Background Survey

The first all-sky maps from the ROSAT survey of the diffuse X-ray background have been released by the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. The maps cover approximately 98 % of the sky in the 1/4 keV, 3/4 keV, and 1.5 keV bands, with an angular resolution of about 2 degrees and high sensitivity for low surface brightness extended features. The effects of non-X-ray contamination and X-rays of solar system origin have been eliminated to the greatest possible extent, but discrete X-ray sources have not been removed. The much improved angular resolution, statistical precision, and completeness of coverage of these maps reveals considerable structure over the entire 0.1 - 2.0 keV energy range that was not observed previously. The data compare well with previous all-sky surveys in terms of absolute normalization and zero point.

The maps were constructed using an equal-area (Aitoff-Hammer) projection. Intensities are in units 10^-6 counts/second/arcmin². The projections are in Galactic coordinates centered at 0 longitude with longitude increasing to the left.

Figure 1. 1/4 keV diffuse background map from the ROSAT all-sky survey. The projection is an Aitoff-Hammer equal-area in galactic coordinates with the Galactic center in the middle. The image shows the general increase in intensity from the Galactic plane to the poles, but it also shows considerable detailed structure never before observed in this energy range.

Credit: The Max Planck Institute for Extraterrestrial Physics, Snowden et al. 1995, ApJ, 454, 643

Figure 2. Map of the column density of Galactic neutral hydrogen in the same projection as Figure 1. Note the general negative correlation between the 1/4 keV diffuse X-ray background of Figure 1 and the neutral hydrogen column density of Figure 2.

Credit: Dickey and Lockman 1990, ARAA, 28, 215

Figure 3. 3/4 keV diffuse background map from the ROSAT all-sky survey in the same projection as Figure 1. The image shows a radically different structure than the 1/4 keV background of Figure 1. At 3/4 keV, the sky is dominated by the relatively smooth extragalactic background and a limited number of bright extended Galactic objects.

Credit: The Max Planck Institute for Extraterrestrial Physics, Snowden et al. 1995, ApJ, 454, 643

Figure 4. ROSAT 1.5 keV band map. This image of the X-ray sky is similar to the 3/4 keV map except that the Galactic contribution is reduced.

Credit: S.L. Snowden et al. 1995, The Astrophysical Journal, Vol. 454, pp. 643-653 and MPE