The NGC 454 system: anatomy of a mixed on-going merger

TL;DR

This study characterizes the ongoing merger between two galaxies in the NGC 454 system through multi-wavelength observations and simulations, revealing complex kinematics and an advanced interaction stage.

Contribution

It provides a detailed multi-lambda analysis and SPH simulations that elucidate the dynamics and future evolution of the NGC 454 galaxy pair, a previously less understood merger.

Findings

NGC 454 E is an S0 galaxy with interaction-induced distortions.

Star forming complexes are connected by a faint tail in NGC 454 W.

The system is in an advanced merger stage, likely to coalesce in about 0.2 Gyr.

Abstract

This paper focuses on NGC 454, a nearby interacting pair of galaxies (AM0112-554, RR23), composed of an early-type (NGC 454 E) and a star forming late-type companion (NGC 454 W). We aim at characterizing this wet merger candidate via a multi-lambda analysis, from near-UV to optical using SWIFT-UVOT, and mapping the Halpha intensity (I) distribution, velocity (Vr), and velocity dispersion (sigma) fields with SAM+Perot-Fabry at SOAR observations. Luminosity profiles suggest that NGC 454 E is an S0. Distortions in its outskirts caused by the on-going interaction are visible in both optical and near-UV frames. In NGC 454 W, the NUV-UVOT images and the Halpha show a set of star forming complexes connected by a faint tail. Halpha emission is detected along the line connecting NGC 454 E to the NGC 454 main HII complex. We investigate the (I-sigma), (I-Vr ) (Vr-sigma) diagnostic diagrams of the HII complexes, most of which can be interpreted in a framework of expanding bubbles. In the main HII complex, enclosed in the UV brightest region, the gas velocity dispersion is highly supersonic reaching 60 km/s. However, Halpha emission profiles are mostly asymmetric indicating the presence of multiple components with an irregular kinematics. Observations point towards an advanced stage of the encounter. Our SPH simulations with chemophotometric implementation suggest that this mixed pair can be understood in terms of a 1:1 gas/halos encounter giving rise to a merger in about 0.2 Gyr from the present stage.