Unravelling the Post-Collision Properties of the Cartwheel Galaxy: A MUSE Exploration of its Bar and Inner Region

TL;DR

This study uses MUSE IFU observations to analyze the stellar kinematics, age, and gas properties of the Cartwheel galaxy's inner region, revealing a surviving stellar bar and insights into its post-collision evolution.

Contribution

It provides new kinematic and stellar population evidence for a pre-existing stellar bar that survived the galaxy's collision, enhancing understanding of collisional galaxy evolution.

Findings

Detection of a stellar bar in the inner region supporting previous NIR imaging

Evidence of a stellar population age gradient indicating a pre-collision bar

Absence of active galactic nucleus activity in the galaxy center

Abstract

Aims: To investigate the characteristics of the bar and inner disk in the collisional ring galaxy Cartwheel. Methods: We used the Integral Field Unit (IFU) observations with Multi-Unit Spectroscopic Explorer (MUSE) of the Very Large Telescope (VLT) to investigate the stellar kinematics, age, and nature of ionised gas in the inner region of the Cartwheel. We produced the stellar line of sight (LOS) velocity (V), velocity dispersion ($\sigma$), h$_3$ velocity moment, stellar population age, and emission-line maps of the galaxy using the Galaxy IFU Spectroscopy Tool (GIST) pipeline. Results: The observed nature of intensity, V, and $\sigma$ profiles altogether support the existence of a stellar bar as earlier revealed from near-infrared (NIR) $K_s$ band imaging. A weak correlation between V/$\sigma$ and h$_3$ is found within the bar radius, providing more kinematic evidence for a stellar bar which survived the drop-through collision. The overall weak anti-correlation between V/$\sigma$ and h$_3$ in the disk implies that the stellar orbits in the disk are less stable, which might be due to the impact of the collision. The mass-weighted age map of the galaxy shows that the stellar populations in the bar region are relatively older, with an increasing gradient from the bar edge to the centre, another evidence to signify that the bar was present before the galaxy underwent collision. We do not find an active galactic nuclei (AGN) from the BPT analysis of a central unresolved source reported earlier using NIR imaging. Our findings provide the preservation of the pre-collisional structures in the inner region of the Cartwheel, an important input to understanding the evolution of collisional galaxy systems, particularly investigating the pre-collisional central region for theoretical studies.