  Using cosmological hydrodynamical zoom-in simulations, we explore the
properties of subhalos in Milky Way analogs that contain a sub-component of
Atomic Dark Matter (ADM). ADM differs from Cold Dark Matter (CDM) due to the
presence of self interactions that lead to energy dissipation and bound-state
formation, analogous to Standard Model baryons. This model can arise in complex
dark sectors that are natural and theoretically-motivated extensions to the
Standard Model. The simulations used in this work were carried out using GIZMO
and utilize the FIRE-2 galaxy formation physics in the Standard Model baryonic
sector. For the parameter points we consider, the ADM gas cools efficiently,
allowing it to collapse to the center of subhalos. This increases a subhalo's
central density and affects its orbit, with more subhalos surviving small
pericentric passages. The subset of subhalos that host visible satellite
galaxies have cuspier density profiles and smaller stellar-half-mass radii
relative to CDM. The entire population of dwarf galaxies produced in the ADM
simulations is much more compact than those seen in CDM simulations, unable to
reproduce the entire diversity of observed dwarf galaxy structures.
Additionally, we also identify a population of highly compact subhalos that
consist nearly entirely of ADM and form in the central region of the host,
where they can leave distinctive imprints in the baryonic disk. This work
presents the first detailed exploration of subhalo properties in a strongly
dissipative dark matter scenario, providing intuition for how other regions of
ADM parameter space, as well as other dark sector models, would impact
galactic-scale observables.
