Unveiling galaxy structures: systematic analysis of bulge + disc decomposition using simulated JWST/NIRCam observations

Abstract

Characterizing and accurately decomposing galaxies into structural components, such as bulges and discs, is essential for understanding galaxy formation and evolution, particularly at high redshift, where galaxies are compact and faint. Leveraging the unparalleled resolution and sensitivity of JWST and imaging data from CEERs programme, we simulate galaxies with bulge + disc components and assess the effectiveness of single and double Sérsic model fittings, respectively. We first evaluate the performance of single Sérsic fits, and find it can recover total magnitudes (i.e. within 0.5 mag), and size (i.e. within 0.2 dex), down to 27 mag. The features that emerged in the residual map can properly reflect the underlying two-component structures. We also show that Sérsic indices can serve as proxies for the bulge-to-total flux ratio (B/T). For double Sérsic models, we find comparable accuracy in recovering bulge and disc magnitudes (i.e. within 0.5 mag), and effective radius (i.e. within 0.2 dex), down to 26 mag. To quantitatively determine whether a double Sérsic model better describes our two-component systems compared to a single Sérsic profile, we evaluate the Bayesian Information Criterion for both model configurations. To extend the applicability of our results to other NIRCam programmes, we evaluate the signal-to-noise ratio (SNR) of the simulated galaxies and find that model parameters are reliably reproduced when the SNR exceeds 10. Our work demonstrates the detailed morphological measurement uncertainties using single and double Sérsic models, which provides an essential reference for future JWST/NIRCam-based morphological studies, especially for high-redshift galaxies.