Formation of an Ultra Diffuse Satellite Galaxy

The formation of ultra diffuse galaxies within the ΛCDM model remains an open question, and is central to addressing the need for galaxy formation models to produce a wide variety of low-mass galaxy morphologies. We identified 36 ultra diffuse satellite galaxies (UDSGs) around MW-mass hosts in the FIRE-2 simulations, and we selected an analogue to the Antlia 2 galaxy for further study. Our analysis of the analogue galaxy evolution indicates that it underwent a tidal shock near its first pericenter passage as it came within < 10 kpc of its host. The analogue galaxy subsequently experienced significant tidal stripping of its dark matter and puffing up of its stellar distribution, causing it to transform from an average-sized galaxy into an ultra diffuse galaxy. In agreement with current estimates for Antlia 2 within ΛCDM cosmology, we find that the analogue galaxy has lost over 98% of its dark matter from infall to z=0 while retaining most of its stellar mass. We compared the sizes of typical satellite galaxies to our UDSGs to contextualize their morphology in our model. We find that UDSGs display a wide range of galaxy sizes of about 2-8 kpc at stellar masses of about 10^6-6.5 M_☉. Pending further analysis, we will explore the mechanisms of UDSG formation by analyzing the shape of the analogue’s dark matter density profile and tidal track at infall and during pericenter passages.