Stellar mass estimation based on IRAC photometry for Spitzer SWIRE-field galaxies

We analyze the feasibility of estimating the stellar mass of galaxies by mid-infrared luminosities based on a large sample of galaxies cross-identified from Spitzer SWIRE fields and the SDSS spectrographic survey. We derived the formulae to calculate the stellar mass by using IRAC 3.6 mu m and 4.5 mu m luminosities. The mass-to-luminosity ratios of IRAC 3.6 mu m and 4.5 mu m luminosities are more sensitive to the star formation history of galaxies than to other factors, such as the intrinsic extinction,. metallicity and star formation rate. To remove the effect of star formation history, we used g-r color to recalibrate the formulae and obtain a better result. Researchers must. be more careful when estimating the stellar mass of low metallicity galaxies using our formulae. Due to the emission from dust heated by the hottest young stars, luminous infrared galaxies present higher IRAC 4.5 mu m luminosities compared to IRAC 3.6 mu m luminosities. For most of type-II AGNs, the nuclear activity cannot enhance 3.6 mu m and 4.5 mu m luminosities compared with normal galaxies. Star formation in our AGN-hosting galaxies is also very weak, almost all of which are early-type galaxies.