Unravelling the post-collision properties of the Cartwheel galaxy: A MUSE exploration of its bar and inner region

¹ Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, Post Bag 4, Pune 411007, India
e-mail: chayanm@iucaa.in; mondalchayan1991@gmail.com
² Indian Institute of Astrophysics, Koramangala II Block, Bangalore 560034, India

Received: 25 July 2023
Accepted: 27 September 2023

Abstract

Aims. We aim to investigate the characteristics of the bar and inner disc in the collisional ring galaxy Cartwheel.

Methods. We used integral field unit (IFU) observations from the 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 galaxy. We produced stellar line of sight velocity (V), velocity dispersion (σ), h₃ 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 the intensity, V, and σ profiles together support the existence of a stellar bar, as earlier revealed from near-infrared (NIR) K_s-band imaging. A weak correlation between V/σ and h₃ is found within the bar radius, providing more kinematic evidence for a stellar bar that survived the drop-through collision. The overall weak anti-correlation between V/σ and h₃ in the disc implies that the stellar orbits in the disc 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 old, with an increasing gradient from the bar edge to the centre, further evidence that the bar was present before the galaxy underwent collision. Using a BPT diagram, we analysed a central unresolved source detected earlier with NIR imaging and do not find evidence of an active galactic nucleus. Our findings signify the preservation of the pre-collisional structures in the inner region of the Cartwheel, an important point to note when attempting to determine the evolution of collisional galaxy systems, particularly when investigating pre-collisional central regions in theoretical studies.