Stars and gas in the Medusa merger

TL;DR

The paper investigates the Medusa galaxy's merger history by combining optical and radio observations with numerical simulations, revealing a minor merger scenario that explains its disturbed appearance and star formation activity.

Contribution

It provides new observational data and simulations supporting a minor merger origin for the Medusa galaxy, highlighting the role of a gas-rich disk galaxy infall.

Findings

Discovery of a 56 kpc HI tail containing about one third of the system's HI mass.

Detection of HI absorption in the galaxy's center and in a nearby galaxy, with limited influence on Medusa's evolution.

Simulations successfully reproduce observed features, supporting a minor merger scenario.

Abstract

The Medusa (NGC 4194) is a well-studied nearby galaxy with the disturbed appearance of a merger and evidence for ongoing star formation. In order to test whether it could be the result of an interaction between a gas-rich disk-like galaxy and a larger elliptical, we have carried out optical and radio observations of the stars and the gas in the Medusa, and performed $N$-body numerical simulations of the evolution of such a system. We used the Nordic Optical Telescope to obtain a deep V-band image and the Westerbork Radio Synthesis Telescope to map the large-scale distribution and kinematics of atomic hydrogen. A single HI tail was found to the South of the Medusa with a projected length of 56 kpc (5') and a gas mass of 7* 10^8 M_sun, thus harbouring about one third of the total HI mass of the system. HI was also detected in absorption toward the continuum in the center. HI was detected in a small nearby galaxy to the North-West of the Medusa at a projected distance of 91 kpc. It is, however, unlikely that this galaxy has had a significant influence on the evolution of the Medusa. The simulations of the slightly prograde infall of a gas-rich disk galaxy on an larger, four time more massive elliptical (spherical) galaxy reproduce most of the observed features of the Medusa.Thus, the Medusa is an ideal object to study the merger-induced star formation contribution from the small galaxy of a minor merger.