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Extended Lyman-alpha emission is now commonly detected around high redshiftgalaxies through stacking and even on individual basis. Despite recentobservational advances, the physical origin of these Lyman-alpha halos (LAHs),as well as their relationships to galaxies, quasars, circumgalactic gas, andother environmental factors remains unclear. We present results from our newLyman-alpha full radiative transfer code voroILTIS which runs directly on theunstructured Voronoi tessellation of cosmological hydrodynamical simulations.We make use of the TNG50 simulation and simulate LAHs from redshift $z=2$ to$z=5$, focusing on star-forming galaxies with $8.0 <\log_{10}{(M_\star/\rm{M}_\odot)} < 10.5$. While TNG50 does not directly followionizing radiation, it includes an on-the-fly treatment for active galacticnuclei and ultraviolet background radiation with self-shielding, which areimportant processes impacting the cooling and ionization of the gas. Based onthis model, we present the predictions for the stacked radial surfacebrightness profiles of Ly$\alpha$ as a function of galaxy mass and redshift.Comparison with data from the MUSE UDF at $z>3$ reveals a promising level ofagreement. We measure the correlations of LAH size and central brightness withgalaxy properties, finding that at the masses of $8.5 \leq \log_{10}\left(M_\star/\rm{M}_\odot\right) \leq 9.5$, physical LAH sizes roughly doublefrom $z=2$ to $z=5$. Finally, we decompose the profiles into contributions fromdiffuse emission and scattered photons from star-forming regions. In oursimulations, we find rescattered photons from star-forming regions to be themajor source in observed LAHs. Unexpectedly, we find that the flattening of LAHprofiles at large radii becomes dominated by photons originating from othernearby halos rather than diffuse emission itself.

The physical origins and dominant emission mechanisms of Lyman-alpha halos: results from the TNG50 simulation in comparison to MUSE observations