ИСТИНА

Ultra-diffuse galaxies (UDGs) have sizes comparable to the Milky Way and stellar masses of about 1/1000 of it. They attracted a lot of attention as possible “dark galaxies” heavily dominated by dark matter, however, no reliable dynamical mass estimates were done because of their extremely low surface brightness. Post-starburst galaxies (PSGs) on the other hand are gas free diffuse young (300–500 Myr) objects with the stellar masses comparable with UDGs, but having somewhat higher surface brightness. We have recently obtained deep spectroscopic observations of Coma cluster with 11 PSG and 40 UDG targets. All PSGs and 7 of UDGs allowed to derive their internal kinematics together with stellar population properties. The dynamical modelling of ultra-diffuse galaxies using JAM routine showed that their dark matter fractions are generally consistent with those of normal galaxies. However the majority of these objects were found to be anisotropic, with beta_z ~ 0.5-0.7. The modelling of PSGs kinematics also demonstrated a high anisotropy, which is not typical for regular stellar disks. This fact advocates for suggestion that PSGs have recently experienced ram pressure stripping of gas, and at least some of them, should they evolve passively, will convert into UDGs on the timescale of 2-5 Gyr due to aging of stellar population and dynamic inflation of their disks.