  We explore the correlation between morphological types and mid-infrared (MIR)
properties of an optically flux-limited sample of 154 galaxies from the Forth
Data Release (DR4) of Sloan Digital Sky Survey (SDSS), cross-correlated with
Spitzer SWIRE (Spitzer Wide-Area InfraRed Extragalactic Survey) fields of
ELAIS-N1, ELAIS-N2 and Lockman Hole. Aperture photometry is performed on the
SDSS and Spitzer images to obtain optical and MIR properties. The morphological
classifications are given based on both visual inspection and bulge-disk
decomposition on SDSS g- and r-band images. The average bulge-to-total ratio
(B/T) is a smooth function over different morphological types. Both the
8um(dust) and 24um(dust) luminosities and their relative luminosity ratios to
3.6um (MIR dust-to-star ratios) present obvious correlations with both the
Hubble T-type and B/T. The early-type galaxies notably differ from the
late-types in the MIR properties, especially in the MIR dust-to-star ratios. It
is suggested that the MIR dust-to-star ratio is an effective way to separate
the early-type galaxies from the late-type ones. Based on the tight correlation
between the stellar mass and the 3.6um luminosity, we have derived a formula to
calculate the stellar mass from the latter. We have also investigated the MIR
properties of both edge-on galaxies and barred galaxies in our sample. Since
they present similar MIR properties to the other sample galaxies, they do not
influence the MIR properties obtained for the entire sample.
