Satellite compaction pathways: environmental drivers shaping dwarf galaxy corpulence in the TNG50 simulation

This study aims to understand the processes that lead to the growth in size of dwarf galaxies, especially those that become compact satellites. We use the TNG50 hydrodynamical simulation to examine dwarf galaxies at z=0 with stellar masses in the range [8.4, 9.2] log(M_*/M_sun) and avoid including systems that may be spurious. Compact dwarfs are distinguished from “Normal” galaxies on the main branch spine by where they lie on the lower envelope of the z=0 size-mass relation of the main branch and lower-size secondary branch. We find two main pathways to compaction. The first pathway involves compact satellites that still have a considerable amount of dark matter and are located

in a sparse environment where there are fewer mergers. Such circumstances are conducive to the accretion of lower-angular-momentum gas, which in turn, causes strong inner star formation and galactic compaction, a phenomenon we have documented in central galaxies. The second pathway operates largely on dark matter deficient satellites, which are usually red and have higher than expected metal content for their stellar mass. The outer stellar components of these satellites are predominantly responsible for their compaction. The process of compaction is observed to be accelerated by at least 15% when gas is present, even when stronger tidal fields are dominant. We also discuss a third pathway that is less certain.

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