Chandra X-ray images of the central part of M 82 integrated over the 13 observations. Top left: 2−4 keV image. Top right: 4−8 keV band. The colour scale of these two images is in logarithmic with the brightest point sources are saturated. Bottom left: The 4−6 keV image of the ellipse where the data of the diffuse emission spectrum were taken. The detected discrete sources were masked. The region where the brightest ULXs along with a few others are clustered is masked in a block. This image is in a linear scale as the dynamic range of the brightness is narrow: 1−19, as a result of the removal of discrete sources. Bottom right: The same image as top right overlaid by the ellipse and the 38 region segments for spatially resolved spectral study.