Metallicity profiles of Ultra Diffuse Galaxies in NIHAO simulations

Supernovae feedback driven expansion has proven to be a viable mechanism to explain the average properties, such as size, colour, mass and internal kinematics, of a large fraction of Ultra Diffuse Galaxies (UDGs). Here, we explore the origin of stellar metallicity gradients in feedback driven simulated UDGs from the NIHAO project and compare them with the observed distribution of metallicity gradients of both Local Group dwarfs as well as of the recently observed UDG DF44. Simulated UDGs display a large variety of metallicity profiles, showing flat to negative gradients, similarly to what is observed in Local Group dwarfs, while DF44 data suggest a flat to positive gradient. The variety of metallicity gradients in simulations is set by the interplay between the radius at which star formation occurs and the subsequent supernovae feedback driven stellar redistribution: rotation supported systems tend to have flat metallicity profiles while dispersion supported galaxies show negative and steep profiles. Our results suggest that UDGs are not peculiar in what regards their metallicity gradients, when compared to regular dwarfs. We predict that UDGs formed via SNae feedback should have flat-to-negative metallicity profiles: desirably, a larger observational sample of UDGs’ gradients shall be available in the future, in order to test our predictions.