Spitzer Infrared Spectrograph (IRS) Mapping of the Inner Kiloparsec of NGC 253: Spatial Distribution of the [Ne III], Polycyclic Aromatic Hydrocarbon 11.3 Micron, and H2 (0-0) S(1) lines and a Gradient in the [Ne III]/[Ne II] Line Ratio

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 on board the Spitzer Space Telescope. The map is centered on the nucleus of the galaxy and spans the inner 800 × 688 pc2. The spatial distribution of the [Ne III] line at 15.55 μm and the polycyclic aromatic hydrocarbon feature at 11.3 μm peaks at the center, while the purely rotational transition of molecular hydrogen at 17.03 μm is strong over several slit positions. We perform a brief investigation of the implications of these measurements on the properties of the star formation in this region, using theories developed to explain the deficiency of massive stars in starbursts.