Star-gas misalignment in galaxies: I. The properties of galaxies from the Horizon-AGN simulation and comparisons to SAMI

TL;DR

This study uses Horizon-AGN simulation to analyze star-gas misalignment in galaxies, finding it correlates with galaxy morphology and gas fraction, and compares results with SAMI observations to understand environmental effects.

Contribution

It demonstrates that Horizon-AGN can reproduce observed misalignment fractions and angles, and explores the environmental dependence of misalignment in galaxies.

Findings

Horizon-AGN matches observed misalignment fractions and angles.

Misalignment is more common in early-type galaxies.

Misalignment increases as gas fraction decreases.

Abstract

Recent integral field spectroscopy observations have found that about 11% of galaxies show star-gas misalignment. The misalignment possibly results from external effects such as gas accretion, interaction with other objects, and other environmental effects, hence providing clues to these effects. We explore the properties of misaligned galaxies using Horizon-AGN, a large-volume cosmological simulation, and compare the result with the result of the Sydney-AAO Multi-object integral field spectrograph (SAMI) Galaxy Survey. Horizon-AGN can match the overall misalignment fraction and reproduces the distribution of misalignment angles found by observations surprisingly closely. The misalignment fraction is found to be highly correlated with galaxy morphology both in observations and in the simulation: early-type galaxies are substantially more frequently misaligned than late-type galaxies. The gas fraction is another important factor associated with misalignment in the sense that misalignment increases with decreasing gas fraction. However, there is a significant discrepancy between the SAMI and Horizon-AGN data in the misalignment fraction for the galaxies in dense (cluster) environments. We discuss possible origins of misalignment and disagreement.