The Mysterious Merger of NGC6868 and NGC6861 in the Telescopium Group

TL;DR

This study uses Chandra X-ray data to analyze the interaction and merger history of two dominant galaxies in the Telescopium group, revealing gas sloshing, cold fronts, and complex thermal structures indicative of ongoing merging processes.

Contribution

It provides detailed X-ray observations and analysis of the gas dynamics and merger signatures in NGC6868 and NGC6861, offering new insights into galaxy group interactions.

Findings

Detection of cold front and spiral-shaped tail in NGC6868 indicating gas sloshing.

Evidence of hot gas sheaths and bifurcated tails around NGC6861 suggesting complex merger activity.

Constraints on galaxy motion and merger dynamics from temperature and density maps.

Abstract

We use Chandra X-ray observations of the hot gas in and around NGC6868 and NGC6861 in the Telescopium galaxy group (AS0851) to probe the interaction history between these galaxies. Mean surface brightness profiles for NGC6868 and NGC6861 are each well described by double beta-models, suggesting that they are each the dominant galaxy in a galaxy subgroup about to merge. Surface brightness and temperature maps of the brightest group galaxy NGC6868 show a cold front edge ~23 kpc to the north, and a cool 0.62 keV spiral-shaped tail to the south. Analysis of the temperature and density across the cold front constrains the relative motion between NGC6868 and the ambient group gas to be at most transonic; while the spiral morphology of the tail strongly suggests that the cold front edge and tail are the result of gas sloshing due to the subgroup merger. The cooler central region of NGC6861 is surrounded by a sheath of hot gas to the east and hot, bifurcated tails of X-ray emission to the west and northwest. We discuss supersonic infall of the NGC6861 subroup, sloshing from the NGC6868 and NGC6861 subgroup merger, and AGN heating as possible explanations for these features, and discuss possible scenarios that may contribute to the order of magnitude discrepancy between the Margorrian and black hole mass - sigma predictions for its central black hole.