Color gradients in nearby galaxies with the DESI Imaging Legacy Survey

Li-Wen Liao^1,2*, Andrew P. Cooper^1,2

¹Institute of Astronomy, National Tsing Hua University, Hsinchu, Taiwan
²Center for Informatics and Computation in Astronomy, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Li-Wen Liao, email:liwen@gapp.nthu.edu.tw

Radial color gradients within galaxies arise from stellar population gradients. Large samples of color gradients can be measured in wide-area imaging surveys to complement much smaller samples of spectroscopic IFU observations and provide statistical constraints on galaxy evolution models. Here we measure color gradients for low-redshift galaxies (z<0.1) using photometry from the DESI Legacy Imaging Survey. Our sample comprises ~63,000 galaxies with spectroscopic redshifts and ~480,000 galaxies with photometric redshifts. We find the color gradients of most galaxies in this sample are negative (redder in the center), consistent with the literature. We investigate the relationship between color gradient, overall g-r and r-z color, Mr, M*, and sSFR. We find that redder galaxies tend to have steeper color gradients. Trends of gradients with Mr (M*) show an inflection around Mr~ -21 (log10 M*/Msun ~10.5). For less massive galaxies, color gradients become steeper with increasing M*, whereas color gradients in more massive galaxies become shallower. We also compute color gradients for Illustris-TNG galaxies using mock SDSS images. The trends with Mr and M* in the simulation are consistent with our observational results but the trends of g-r and sSFR behave differently. We attribute this to an excess of low-redshift star formation in massive TNG galaxies. Overall, our results support concordance ΛCDM galaxy formation theory, in which galaxies assemble inside-out through dissipative collapse and star formation is strongly suppressed by AGN feedback above a critical mass.

Keywords: galaxies, galaxies: formation, galaxies: structure, galaxies: general