The Effects of the WISE/GALEX Photometry for the SED-Fitting with M31 Star Clusters and Candidates

Abstract

Spectral energy distribution (SED) fitting of stellar population synthesis models is an important and popular way to constrain the physical parameters ---e.g., the ages, metallicities, masses for stellar population analysis. The previous works suggest that both blue-bands and red-bands photometry works for the SED-fitting. Either blue-domained or red-domained SED-fitting usually lead to the unreliable or biased results. Meanwhile, it seems that extending the wavelength coverage could be helpful. Since the Galaxy Evolution Explorer ({\it GALEX}) and Wide-field Infrared Survey Explorer (WISE) provide the FUV/NUV and mid-infrared $W1$/$W2$ band data, we extend the SED-fitting to a wider wavelength coverage. In our work, we analyzed the effect of adding the FUV/NUV and $W1$/$W2$ band to the optical and near-infrared $UBVRIJHK$ bands for the fitting with the Bruzual \& Charlot 2003 (BC03) models and {\sc galev} models. It is found that the FUV/NUV bands data affect the fitting results of both ages and metallicities much more significantly than that of the WISE $W1$/$W2$ band with the BC03 models. While for the {\sc galev} models, the effect of the WISE $W1$/$W2$ band for the metallicity fitting seems comparable to that of {\it GALEX} FUV/NUV bands, but for age the effect of the $W1$/$W2$ band seems less crucial than that of the FUV/NUV bands. Thus we conclude that the {\it GALEX} FUV/NUV bands are more crucial for the SED-fitting of ages and metallicities, than the other bands, and the high-quality UV data (with high photometry precision) are required.