Massive disk galaxies with high surface brightness plus low surface brightness stellar disks, hosted by massive dark matter halo -- a TNG50 simulation study

Abstract: We study massive disk galaxies (total stellar mass$&gt;=10<sup>{11}$ $\mathrm{M_{\odot}}$) from IllustrisTNG50 simulation, and perform 2-D structural decomposition of the galaxies using their idealised, synthetic SDSS images for z=0. We find an interesting sample of galaxies having a central high surface brightness (HSB) stellar disk, surrounded by an extended low surface brightness (LSB) stellar disk, similar to giant LSB galaxies. These massive, double-exponential disk galaxies are found to be hosted by dark matter haloes of $\sim 10^{12} \mathrm{M_{\odot}}$ in agreement to observations of such galaxies. Their maximum rotation velocity, an approximate measure of their dynamical mass, lies within $\sim$ (300-500) km/s. The stellar-to-dark matter mass ratio and the baryon-to-dark matter mass ratio of the sample lies in the range of $\sim$ (0.04 - 0.46) and $\sim$ (0.07 - 0.47) respectively. Our results show that cosmological simulations are able to form disc galaxies with HSB plus LSB disks, as in observations.