Massive double-exponential disk galaxies with outer, extended low surface brightness stellar disk

The formation and evolution of the most massive (stellar mass = 10**11 solar mass) disk galaxies in the nearby universe represents many intriguing questions. One class of such galaxies are the giant low surface brightness galaxies. Several of them ( e.g, Malin 1, UGC 1382, UGC 1378 etc) are observed to have a central high surface brightness exponential disk surrounded by a photometrically distinct, extended (R_d more than 10 kpc) low surface brightness stellar disk. Several mechanisms e.g., accretion of dwarf satellites in the outskirt of the host galaxy, interaction with another galaxy, or even secular evolution have been suggested to create such hybrid morphology. We aimed to build a sample of such massive double-exponential disk galaxies from cosmological simulations in order to understand the mass assembly process across cosmic time. We used IllustrisTNG50 data and performed 2D light modeling on the synthetic SDSS-g band images of disk galaxies (M_star>=10^11 solar mass) made from TNG50 data. We found 7 galaxies (12% of the parent sample) to show HSB plus extended LSB structure, similar to the observed counterparts. The simulated double-disk galaxies are found to lie in the green-valley region of the sSFR vs M_star plane and also satisfy Baryonic Tully-Fisher relation (Sarkar S., Saha K., arXiv:2409.20309). We aim to study the mass assembly process and the survival process of the outer faint envelope of these galaxies in the follow-up work.