Stellar mass-size relation for the central disk galaxies with tiny stellar halos we selected in the TNG50 simulation at z = 0. A linear fit of the mass-size correlation is represented by the solid black line. We categorize galaxies based on their deviation within ±0.5σ from the linear fit, as the dashed lines indicate. Galaxies falling within the range of −0.5σ to 0.5σ are identified as ‘normal galaxies’ (green dots), those exceeding 0.5σ are labeled as ‘extended galaxies’ (blue dots), and those falling below −0.5σ are designated as ‘compact galaxies’ (red dots). The dotted lines partition the galaxies into four mass bins (M1–M4) encompassing 10^{9 − 9.5} M_⊙, 10^{9.5 − 10} M_⊙, 10^{10 − 10.5} M_⊙, and 10^{10.5 − 11.5} M_⊙. The bottom of this figure provides the count of galaxies of each type within M1–M4.