Li-Wen Liao (NTHU); Andrew Cooper (NTHU)
Color gradients trace radial variations of age and metallicity in galaxies. They may help to distinguish between different models for how and when stellar mass was assembled in galaxies of a given present day mass and average color. Previous work on the correlation of color gradients with average color and magnitude has focused on early-type galaxies and dense environments. Only a few studies discussed the color gradient in spiral galaxies. To improve our understanding of color gradients across the bulk of the galaxy population, we use photometry from DR8 of the DESI Legacy Imaging Survey (LS), which reaches r ~ 24 over ~14,000 deg2. Here we present a study of g-r and r-z color gradients and their correlations with other galaxy properties for 47,000 bright LS galaxies with SDSS spectra. Consistent with the literature, we find almost all galaxies are redder at the center than in the outskirts, and there is a clear trend for galaxies with redder average g-r colors to have relatively redder cores (steeper gradients). The same trend is seen with increasing absolute magnitude (and stellar mass), but reverses at Mr >~ -21 such that the brightest galaxies have shallower gradients. This could be explained by the mixing of stellar populations in mergers. We compare our results to the predictions of the Illustris TNG-100 simulation.