2004ApJS..154..281I

We investigate the density structure of the interstellar medium using new high-resolution maps of the 8, 24, and 70 µm surface brightness toward a molecular cloud in the Gum Nebula, made as part of the Spitzer Space Telescope Galactic First Look Survey. The maps are correlated with 100 µm images measured with IRAS. At 24 and 70 µm, the spatial power spectrum of surface brightness follows a power law with a spectral index of -3.5. At 24 µm, the power-law behavior is remarkably consistent from the ∼0°.2 size of our maps down to the ∼5" spatial resolution. Thus, the structure of the 24 µm emission is self-similar even at milliparsec scales. The combined power spectrum produced from Spitzer 24 µm and IRAS 25 µm images is consistent with a change in the power-law exponent from -2.6 at spatial wavenumber k∼2x10^–3/arcsec to -3.5 at k∼4x10^–3/arcsec. The decrease may be due to the transition from a two-dimensional to three-dimensional structure. Under this hypothesis, we estimate the thickness of the emitting medium to be 0.3 pc.