Comparison of the spectrum of SN 2024igg (solid black) at −13.9 days relative to B-band maximum, the synthetic spectrum using TARDIS (dashed blue), and a spectrum taken from the carbon-rich CSM interaction model (solid orange, labeled CSM_M2023) (Maeda et al. 2023). The spectrum of SN 2024igg has been calibrated by the photometry and corrected for reddening and host redshift. The flux density of the spectrum of CSM_M2023, with a CSM mass of 0.1 M_⊙, is multiplied by a factor of 0.14 to match the emission peak at ∼6500 Å for visual comparison. The decomposition of the TARDIS spectrum is also shown in the plot, with the positive emission and negative absorption components labeled as different colors. The absorption features of C II and O I are denoted by vertical lines.