Tidal features as tracers of galaxy merger histories: the colours of tidal features in HSC-SSP

TL;DR

This study analyzes the colours of tidal features in a large galaxy sample to understand merger histories, revealing correlations between tidal feature types, galaxy mass, and merger characteristics, thus providing insights into galaxy evolution.

Contribution

It introduces a method to use tidal feature colours as tracers of galaxy merger properties, validated by comparison with existing observational and simulation data.

Findings

Redder outskirts in tidal feature-hosting galaxies suggest accretion from gas-poor minor mergers.

Mass ratios of tidal features decrease with increasing galaxy mass.

Streams are associated with less massive mergers than shells.

Abstract

We measure the radial $g-i$ colour profiles of $\sim$32,000 galaxies drawn from the Hyper Suprime-Cam Subaru Strategic Program optical imaging survey, including 1415 exhibiting tidal features. We compare the colour profiles of galaxies with and without tidal features to extract information about the properties of the mergers that created these features. We find negative colour gradients for both galaxies with and without tidal features and find that tidal feature-hosting red sequence galaxies have redder outskirts than their non-tidal feature hosting counterparts, consistent with the outskirts of these galaxies being dominated by stars accreted from gas-poor minor mergers. We find decreasing mass ratios of tidal features-to-host galaxy with increasing galaxy stellar mass, suggesting that less massive galaxies undergo mergers with companions closer in mass than more massive galaxies. Galaxies exhibiting streams have bluer outskirts than those hosting shells, and shells around red sequence galaxies tend to be more massive and have higher mass ratios to their hosts than streams, consistent with streams being formed from mergers with satellites less massive than those responsible for shells. The agreement between our findings and those of other observational and simulation-based works confirms the validity of our methodology and highlights the value of tidal features colours as a probe into the process through which galaxies evolve.