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

TL;DR

The paper addresses how the most massive disk galaxies—with an inner high surface brightness (HSB) disk and an extended outer low surface brightness (LSB) disk—form in a cosmological context. It leverages the TNG50-1 simulation, creates idealised synthetic SDSS images, and applies 2D GALFIT decomposition to identify seven double-disk systems among galaxies with $M_* \ge 10^{11} M_{ m \odot}$. These systems reside in halos of $M_{ m DM} \sim 10^{12} M_{ m \odot}$, exhibit $V_{\max}$ between $290$ and $530$ km s$^{-1}$, and have stellar-to-dark-matter and baryon-to-dark-matter mass ratios in the ranges $[0.04,0.46]$ and $[0.07,0.47]$, respectively. The findings demonstrate that $\Lambda$CDM-based cosmological simulations can reproduce giant LSB-like disks and offer insights into their formation and mass distribution in the massive-disk regime.

Abstract

We study massive disk galaxies (total stellar mass$>=10^{11}$ $\mathrm{M_{\odot}}$) 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.

Figures (1)

• Figure 1: Two examples of the massive double-exponential disk galaxies obtained from TNG50-1. Left column: Synthetic SDSS g-band idealised images (displayed in gray scale), shown using the same color bar (in log stretch). Subhalo IDs, i.e., galaxy IDs are mentioned in the images. Middle column: Plot of the 1D surface brightness profiles (red data points) obtained from elliptical isophote fitting of the images. The best-fit central sersic (blue dotted curve), inner (magenta dashed curve) and outer exponential (green dash-dotted curve) disk profiles, calculated analytically from the corresponding best-fit 2D GALFIT model, are over-plotted on the above 1-D surface brightness profile. The total,i.e, the analytical sum of the GALFIT model profiles (black solid curve), agrees well with the 1-D profile of each galaxy. Right column: Residual images obtained from GALFIT modeling, displayed following the same color bar (in log stretch).