Spitzer Space Telescope view of diffuse near-infrared continuum emission in the Galaxy

The Infrared Array Camera (IRAC) multiband images from the Spitzer Space Telescope First Look Survey of two 1degreesx5' areas of diffuse interstellar medium (ISM) are used to study the near-infrared (NIR; 2-5 mum) continuum emission and its relation to the mid-infrared (6-10 mum) aromatic features in emission (AFEs). We illustrate that the high sensitivity and spatial resolution of IRAC make it possible to separate the extended emission from stars independently of any model of the distribution of stars in the Galaxy. It is shown that the two independently observed areas have similar colors. Taking into account the current IRAC calibration uncertainties, these colors agree with previous Cosmic Background Explorer measurements in the Galaxy and with Infrared Space Observatory spectra of the ISM in normal star-forming galaxies. Our results imply that the average 3-10 mum spectral shape of the ISM emission does not vary significantly from diffuse sources to star-forming regions, suggesting a close physical relation between the carriers of the NIR continuum and AFEs.