Formation of Ultra-diffuse Galaxies in the field and in galaxy groups

We study ultra-diffuse galaxies (UDGs) in zoom in cosmological simulations, compar- ing UDGs in the field and in galaxy groups. We find that while field dwarfs puff up to UDGs by multiple episodes of supernova feedback (Di Cintio et al.), as satellites, they become quiescent and diffuse by ram-pressure stripping and tidal puffing up. The field and group UDGs share surprisingly similar properties, independent of distance from the host-halo center. Their dark-matter halo mass is in a characteristic narrow mass range log(Mvir/M⊙) = 10.6 ± 0.4, with a typical spin parameter, a particularly low concentration, and a flat core that dominates within the stellar effective radius. Their stellar components are of a characteristic mass range log(M⋆/M⊙) = 7.8 ± 0.6, and tend to have a prolate shape although the surface density profiles have a Sersic indices ∼ 1. Ram-pressure removes the gas from the group UDGs when they are at pericenter, quenching star formation in them and making them redder. This gener- ates a color/star-formation-rate gradient with distance from the host-halo center, as observed in clusters. We find that ∼ 20 per cent of the field UDGs survive as satel- lite UDGs after falling into a massive halo. In addition, less diffuse field galaxies on highly eccentric orbits can become UDGs near pericenter due to tidal puffing up, which contribute an almost equal amount to the group-UDG population. We interpret our findings using simple toy models.  

Speaker: 
Fangzhou Jiang
Place: 
KIAA-PKU Auditorium
Time: 
Friday, November 2, 2018 - 4:00pm to 5:00pm