What drives the corpulence of galaxies? I. The formation of central compact dwarf galaxies in TNG50
Abhner P. De Almeida, Gary A. Mamon, Avishai Dekel, Gast~ao B. Lima Neto
arXiv:2404.15482v1 Announce Type: new
Abstract: Nearby dwarf galaxies display a variety of effective radii (sizes) at given stellar mass, suggesting different evolution scenarios according to their final “stellar” size. The TNG hydrodynamical simulations present a bimodality in the z = 0 size-mass relation (SMRz0) of dwarf galaxies, at $r_{1/2,star}$ ~ 450 pc. Using the TNG50 simulation, we explore the evolution of the most massive progenitors of dwarf galaxies (z=0 $log( M_star / mathrm{M}_odot)$ between 8.4 and 9.2) that ended up as central galaxies of their groups. We split these dwarfs into three classes of the SMRz0: Normals from the central spine of the main branch and Compacts from the secondary branch as well as from the lower envelope of the main branch. Both classes of Compacts see their stellar sizes decrease since z ~ 1 in contrast to Normals, while the sizes of the gas and dark matter (DM) components keep increasing (as for Normals). A detailed analysis reveals that Compacts live in poorer environments, thus suffer fewer major mergers since z=0.8 that otherwise pump angular momentum into the gas, allowing strong gas inflows, producing inner star formation, hence the buildup of a stellar core. Compacts are predicted to be rounder and with bluer cores. Compact dwarfs of similar sizes are observed in the GAMA survey, but the bimodality in sizes is less evident and the most compact dwarfs tend to be passive rather than star forming as in TNG50. Therefore, our conclusions should be confirmed with future cosmological hydrodynamical simulations.arXiv:2404.15482v1 Announce Type: new
Abstract: Nearby dwarf galaxies display a variety of effective radii (sizes) at given stellar mass, suggesting different evolution scenarios according to their final “stellar” size. The TNG hydrodynamical simulations present a bimodality in the z = 0 size-mass relation (SMRz0) of dwarf galaxies, at $r_{1/2,star}$ ~ 450 pc. Using the TNG50 simulation, we explore the evolution of the most massive progenitors of dwarf galaxies (z=0 $log( M_star / mathrm{M}_odot)$ between 8.4 and 9.2) that ended up as central galaxies of their groups. We split these dwarfs into three classes of the SMRz0: Normals from the central spine of the main branch and Compacts from the secondary branch as well as from the lower envelope of the main branch. Both classes of Compacts see their stellar sizes decrease since z ~ 1 in contrast to Normals, while the sizes of the gas and dark matter (DM) components keep increasing (as for Normals). A detailed analysis reveals that Compacts live in poorer environments, thus suffer fewer major mergers since z=0.8 that otherwise pump angular momentum into the gas, allowing strong gas inflows, producing inner star formation, hence the buildup of a stellar core. Compacts are predicted to be rounder and with bluer cores. Compact dwarfs of similar sizes are observed in the GAMA survey, but the bimodality in sizes is less evident and the most compact dwarfs tend to be passive rather than star forming as in TNG50. Therefore, our conclusions should be confirmed with future cosmological hydrodynamical simulations.

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