Galaxies are observed to be lopsided, meaning that they are more massive and
more extended along one direction than the opposite. However, the galaxies
generated in cosmological simulations are much less lopsided, inconsistent with
observations. In this work, we provide a statistical analysis of the lopsided
morphology of 2148 simulated isolated satellite galaxies generated by TNG50-1
simulation, incorporating the effect of tidal fields from halo centres. We
study the radial alignment (RA) between the major axes of satellites and the
radial direction of their halo centres within truncation radii of $3{R}_{h}$ ,
$5{R}_{h}$ and $10{R}_{h}$ . According to our results, RA is absent for all these
truncations. We also calculate the far-to-near-side semi-axial ratios of the
major axes, denoted by ${a}_{-}/{a}_{+}$ , which measures the semi-axial ratios of the
major axes in the hemispheres between backwards (far-side) and facing
(near-side) the halo centres. If the satellites are truncated within radii of
$3{R}_{h}$ and $5{R}_{h}$ with ${R}_{h}$ being the stellar half mass radius, the numbers of
satellites with longer semi-axes on the far-side are found to be almost equal
to those with longer semi-axes on the near-side. Within a larger truncated
radius of $10{R}_{h}$ , the number of satellites with axial ratios ${a}_{-}/{a}_{+}<1.0$ is
about $10\mathrm{\%}$ more than that with ${a}_{-}/{a}_{+}>1.0$ . Therefore, the tidal fields
from halo centres play a minor role in the generation of lopsided satellites.
The lopsidedness radial alignment (LRA), i.e., an alignment of long
semi-major-axes along the radial direction of halo centres, is further studied.
No clear evidence of LRA is found in our sample within the framework of
$\mathrm{\Lambda}$ CDM Newtonian dynamics. In comparison, the LRA can be naturally
induced by the external fields from the central host galaxy in Milgromian
dynamics. (See paper for full abstract)

PREPRINT

# Shape asymmetries and lopsidedness-radial-alignment in simulated galaxies

Jinzhi Shen, Xufen Wu, Yirui Zheng, Beibei Guo

Submitted on 7 November 2022

## Abstract

## Preprint

Comment: 16 pages, 12 figures, 3 tables, submitted to MNRAS

Subject: Astrophysics - Astrophysics of Galaxies