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Abstract

Highly resolved images of the edge-on galaxy NGC 7814 from 2MASS and Spitzer were used to extract the morphologies and spectral energy distributions (SEDs) of the disk, bulge and halo components of this galaxy over a wavelength range from 1.25 to 24 μm. This represents the first direct determination of the mid-infrared emission of the bulge and halo components of a galaxy other than the Milky Way. The SEDs of all three structures imply the presence of emission components from direct stellar light and from at least one further component. For the disk, this further component is interpreted as dust emission having properties typical of star forming disks. The emission from the bulge and the halo is very significantly in excess of that from an extrapolation of the near infrared emission from stars. This excess has a flat spectrum between 8 and 24 μm bands and has an unknown origin. I discuss potential explanations such as dust emission in an interstellar medium, galactic winds, star forming regions and circumstellar dust, as well as emission from brown dwarfs. Further analysis is needed to test these hypotheses.