The observability of galaxy merger signatures in nearby gas-rich spirals

TL;DR

This study uses high-resolution galaxy merger simulations to evaluate how well different stages of galaxy mergers can be identified through morphological and kinematic asymmetries in synthetic images and velocity maps, aiding observational detection.

Contribution

It introduces a method combining photometric and kinematic asymmetries to improve merger detection rates across various phases and observational field-of-view limitations.

Findings

66% completeness in identifying mergers between first pericentre and 500 Myr after coalescence

Detection rates increase to 97% in merging and post-coalescence phases

Combined asymmetry cut-off boosts overall detection to 89%, nearly 100% in advanced phases

Abstract

Galaxy mergers are crucial to understanding galaxy evolution, therefore we must determine their observational signatures to select them from large IFU galaxy samples such as MUSE and SAMI. We employ 24 high-resolution idealised hydrodynamical galaxy merger simulations based on the "Feedback In Realistic Environment" (FIRE-2) model to determine the observability of mergers to various configurations and stages using synthetic images and velocity maps. Our mergers cover a range of orbital configurations at fixed 1:2.5 stellar mass ratio for two gas rich spirals at low redshift. Morphological and kinematic asymmetries are computed for synthetic images and velocity maps spanning each interaction. We divide the interaction sequence into three: (1) the pair phase; (2) the merging phase; and (3) the post-coalescence phase. We correctly identify mergers between first pericentre passage and 500 Myr after coalescence using kinematic asymmetry with 66% completeness, depending upon merger phase and the field-of-view of the observation. We detect fewer mergers in the pair phase (40%) and many more in the merging and post-coalescence phases (97%). We find that merger detectability decreases with field-of-view, except in retrograde mergers, where centrally concentrated asymmetric kinematic features enhances their detectability. Using a cut-off derived from a combination of photometric and kinematic asymmetry, we increase these detections to 89% overall, 79% in pairs, and close to 100% in the merging and post-coalescent phases. By using this combined asymmetry cut-off we mitigate some of the effects caused by smaller fields-of-view subtended by massively multiplexed integral field spectroscopy programmes.