The Formation of Dwarf Galaxy Disks

Abstract Dwarf galaxies are dark matter-dominated systems that are sensitive to feedback and display a diversity of baryonic morphologies. This makes them excellent probes for understanding dark matter and galaxy evolution. This work investigates the physical processes that influence the sizes of isolated dwarf galaxies using high-resolution cosmological zoom-in simulations of 39 dwarf galaxies drawn from the Marvelous Massive Dwarfs simulation suite (7.5 < log ( M ⋆ / M ⊙ ) < 9.1). Our simulations show that dwarf galaxies initially form as compact galaxies ( R e < 2 kpc). However, several of these galaxies (54%) experience periods of gradual size growth at relatively stable specific star formation rate, allowing them to become extended galaxies. While previous simulations have struggled to produce dwarf galaxy disks, we find that the growth of rotation-supported stellar disks is the primary means by which isolated dwarfs become extended in size. These stellar disks are formed by mergers with high orbital angular momentum (AM) satellites on high AM (spiraling-in) orbits, which spin up the gas surrounding the central galaxy and contribute ≈30% of the cold gas mass at z = 0. For these systems, star formation in the AM-supported gas and the gradual buildup of stars in the disk result in secular size growth.