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Boxy/Peanut Bulges: Comparative Analysis of EGIPS Galaxies and TNG50 Models

Anton Smirnov, Alexander Marchuk, Viktor Zozulia, Natalia Sotnikova, Sergey Savchenko

TL;DR

This study analyzes boxy/peanut-shaped (B/PS) bulges in 71 EGIPS galaxies and 20 Illustris TNG50 models by performing a dedicated 2D photometric decomposition that explicitly includes an X-shaped bulge component. The X-shaped bulge is described by an opening angle $\varphi$ and a density truncation scale $s_\mathrm{X}$ with an exponential below the rays (via $h_\mathrm{X}$), allowing measurements such as the B/PS bulge scale $h_\mathrm{X}$ and the bulge-to-total luminosity ratio $X/T$. Key findings show that EGIPS B/PS bulges are larger and more luminous than those in TNG50, while X-structure angles in TNG50 can be unusually small for certain bar orientations; these results imply both projection effects and physical differences in bar properties between real galaxies and simulations. The work highlights the importance of explicitly modeling B/PS bulges in photometric decompositions and how simulation-based bulges and bars compare to observations, with implications for understanding secular evolution in galaxies.

Abstract

We investigated the properties of boxy/peanut-shaped (B/PS) bulges in a sample of 71 galaxies from the Edge-on Galaxies in the Pan-STARRS Survey (EGIPS) and 20 simulated galaxies from Illustris TNG50 using multicomponent photometric decomposition. For each real and simulated galaxy, we obtained a suitable photometric model in which the B/PS bulge was represented by a dedicated 2D photometric function. For real galaxies, we found that more flattened X-structures are generally residing in larger B/PS bulges. When tested against the galaxy masses, we verified that both larger bulges and more flattened X-structures are typically found in more massive galaxies. Since large bars are also known to reside in more massive galaxies, we conclude that the flatness of X-structures in larger B/PS bulges has a physical origin, rather than being solely a result of projection effects due to differences in observed bar viewing angles. When comparing the properties of B/PS bulges between EGIPS galaxies and TNG50 galaxies, with bars rotated for different viewing angles, we found that B/PS bulges in TNG50 are considerably smaller and less luminous in terms of total intensity. This is consistent with previous studies of bar properties in TNG50, indicating the B/PS bulges in TNG50 differ from those in real galaxies, as do their parent bars.

Boxy/Peanut Bulges: Comparative Analysis of EGIPS Galaxies and TNG50 Models

TL;DR

This study analyzes boxy/peanut-shaped (B/PS) bulges in 71 EGIPS galaxies and 20 Illustris TNG50 models by performing a dedicated 2D photometric decomposition that explicitly includes an X-shaped bulge component. The X-shaped bulge is described by an opening angle and a density truncation scale with an exponential below the rays (via ), allowing measurements such as the B/PS bulge scale and the bulge-to-total luminosity ratio . Key findings show that EGIPS B/PS bulges are larger and more luminous than those in TNG50, while X-structure angles in TNG50 can be unusually small for certain bar orientations; these results imply both projection effects and physical differences in bar properties between real galaxies and simulations. The work highlights the importance of explicitly modeling B/PS bulges in photometric decompositions and how simulation-based bulges and bars compare to observations, with implications for understanding secular evolution in galaxies.

Abstract

We investigated the properties of boxy/peanut-shaped (B/PS) bulges in a sample of 71 galaxies from the Edge-on Galaxies in the Pan-STARRS Survey (EGIPS) and 20 simulated galaxies from Illustris TNG50 using multicomponent photometric decomposition. For each real and simulated galaxy, we obtained a suitable photometric model in which the B/PS bulge was represented by a dedicated 2D photometric function. For real galaxies, we found that more flattened X-structures are generally residing in larger B/PS bulges. When tested against the galaxy masses, we verified that both larger bulges and more flattened X-structures are typically found in more massive galaxies. Since large bars are also known to reside in more massive galaxies, we conclude that the flatness of X-structures in larger B/PS bulges has a physical origin, rather than being solely a result of projection effects due to differences in observed bar viewing angles. When comparing the properties of B/PS bulges between EGIPS galaxies and TNG50 galaxies, with bars rotated for different viewing angles, we found that B/PS bulges in TNG50 are considerably smaller and less luminous in terms of total intensity. This is consistent with previous studies of bar properties in TNG50, indicating the B/PS bulges in TNG50 differ from those in real galaxies, as do their parent bars.
Paper Structure (6 sections, 5 equations, 2 figures)

This paper contains 6 sections, 5 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Data
  3. Photometric Decomposition
  4. Preprocessing
  5. General Setup
  6. Photometric Functions

Figures (2)

  • Figure S1: Redshift-derived spectroscopic distance versus absolute stellar magnitude in the $i$ band for the sample of galaxies with boxy/peanut-shaped bulges, studied in the present work.
  • Figure S2: A general scheme of the galaxy processing pipeline used in the present work for EGIPS galaxies (left side) and Illustris TNG50 galaxies (right side).