  We present our early results of the mapping of the nucleus of the starburst
galaxy NGC 253 and its immediate surroundings using the Infrared Spectrograph
onboard the Spitzer Space Telescope. The map is centered on the nucleus of the
galaxy and spans the inner 800 x 688 pc2. The spatial distribution of the
\neiii line at 15.55 microns and the polycyclic aromatic hydrocarbons feature
at 11.3 microns peaks at the center while the purely rotationnal transition of
molecular hydrogen at 17.03 microns is strong over several slit positions. We
perform a brief investigation of the implications of these measurement on the
properties of the star formation in this region using theories developped to
explain the deficiency of massive stars in starbursts.
