Finding massive double-exponential disk galaxies with extended low surface brightness stellar disk -- an IllustrisTNG exploration

TL;DR

This study uses the IllustrisTNG simulation to identify and analyze massive disk galaxies with a distinct double-exponential structure, shedding light on their formation, evolution, and star formation properties.

Contribution

First identification of massive double-exponential disk galaxies in IllustrisTNG simulation, matching observed properties and providing insights into their formation and star formation distribution.

Findings

7 double-disk galaxies identified, representing 12% of the sample.

LSB disk scale lengths range from 9.7 to 31.7 kpc.

Double-disk galaxies align with the Baryonic Tully-Fisher relation.

Abstract

We study massive disk galaxies (stellar mass $>=10^{11}\mathrm{M_{\odot}}$) at z=0 from IllustrisTNG simulation to detect galaxies that contain two exponential stellar disks - a central high surface brightness (HSB) disk surrounded by an extended low surface brightness (LSB) envelope. This is motivated by the observation of several giant LSB galaxies (Malin 1, UGC 1378, UGC 1382 etc), reported in the literature, showing such complex morphology. Studying such systems can help us to understand the mass assembly process and growth of stellar disks in massive galaxies and thus can shed light on massive galaxy formation and evolution scenarios. We use the high-resolution IllustrisTNG50 data and perform Sersic plus exponential profile modeling on the idealized, synthetic SDSS g, r-band images of the massive disk galaxies using GALFIT. We identify 7 disk galaxies (12% of the parent sample of disk galaxies) that are best represented by a central S\'{e}rsic plus a central HSB disk surrounded by an extended LSB disk. The radial scale lengths of the LSB disk lie in the range of $\sim$ 9.7-31.7 kpc, in agreement with that found in the literature. We study the star formation properties of these simulated double-disk galaxies to understand the distribution of these from blue star-forming to red-quenched region. Some of these double-disk galaxies display a characteristic minima in their (g-r) color radial profiles. The double-disk galaxies are found to lie within $\sim$ 1.5-$\mathrm{\sigma}$ region of the Baryonic Tully-Fisher relation from observation.