Several features are evident. There are localized bright spots, corresponding to individual gamma-ray sources. These include active galaxies -- such as 3C 279, the brown spot up and to the right from the center of the picture -- gamma-ray pulsars, and some sources which have not yet been identified with any known object. We also see the band in the inner Milky Way, corresponding to a fairly bright excess from the Galactic plane. This excess was known previously, and remains unexplained; similar comments apply to the bright hump above the Galactic center.
Finally, there is the gamma-ray halo, which appears in shades of blue. Perhaps the biggest surprise is the apparent size of this halo. There has been some previous discussion of the possibility of a gamma-ray halo, but not of the size seen in this image. We note that one should take the details of this image with a grain of salt. Though the image processing we have applied removes much of the noise, it can't possibly get rid of all of it, and the smaller bumps and wiggles in the halo are suspect. It is very clear, however, that the data supports some sort of large scale emission around the Milky Way.
An annotated version of this figure is also available.
