2025ApJ...995...90C

We analyze the morphology of 125 submillimeter galaxies (SMGs) in the PRIMER-COSMOS field using double Sérsic modeling on JWST NIRCam images across six bands (F150W, F200W, F277W, F356W, F410M, and F444W), with SMGs being classified by the bulge Sérsic index (n_bulge) and bulge-to-total luminosity ratio (B/T). The Kolmogorov-Smirnov test between the bright (SFR > 175M_⊙ yr^–1) and the faint groups (SFR < 175M_⊙ yr^–1) reveals no significant statistical differences in morphology across bands. However, we notice that SMGs skew towards higher B/T ratios and lower n_bulge from shorter to longer wavelengths. In F444W, bright SMGs exhibit higher B/T and lower n_bulge, indicating flatter, disturbed bulges, while faint SMGs show lower B/T and higher n_bulge. Notably, SMGs with higher B/T tend to have low Sérsic, challenging the local Universe dichotomy of classical bulges (B/T > 0.5, n > 4) versus pseudo-bulges (B/T < 0.35, n < 2). In the F277W, nonparametric morphological measurements indicate predominantly disk-dominated patterns, with only 24% of SMGs demonstrating merger signatures. After the removal of SMGs with disturbed morphology, the bulge classification scheme in F277W shows pseudo-bulges (21%) and clump migration bulges (16%) from secular evolution, compared to 4% merger-built bulges. Surprisingly, 48% of SMGs defy the classification scheme, showing high B/T (∼0.7) but low Sérsic index (n_bulge ≤ 1). Bars are confirmed in 7% of SMGs. This work suggests that secular evolution takes precedence over major mergers, supporting the idea that isolated evolution fueled by filamentary gas inflow plays a nonnegligible role in the formation of SMGs.