Resolved UV and Optical Color Gradients Reveal Environmental Influence on Galaxy Evolution at Redshift z ∼ 1.6

The changes in colors across a galaxy are intimately connected to the galaxy’s formation, growth, quenching history, and dust content. A particularly important epoch in the growth of galaxies is near z ∼ 2, often referred to as “cosmic noon,” where galaxies on average reach the peak of their star formation. We study a population of 125 cluster galaxies at z ∼ 1.6 in three Hubble Space Telescope filters, F475W, F625W, and F160W, roughly corresponding to the rest-frame far-ultraviolet, near-ultraviolet, and r band, respectively. By comparing to a control sample of 200 field galaxies at similar redshift, we reveal clear, statistically significant differences in the overall spatially resolved colors and color gradients in galaxies across these two different environments. On average, cluster galaxies have redder ultraviolet colors in both the inner and outer regions bounded by r 50, as well as an overall wider dispersion of outside-in color gradients. The presence of these observed differences, along with evidence from ancillary data from previous studies, strongly suggests that the environment drives these population-level color differences, by affecting the stellar populations and/or dust content.