Connecting traces of galaxy evolution: the missing core mass -- morphological fine structure relation

TL;DR

This study reveals an inverse correlation between core mass depletion and fine structure prominence in early-type galaxies, linking galaxy interactions, SMBH activity, and morphological evolution over cosmic timescales.

Contribution

It demonstrates a quantitative relationship between core depletion and fine structures, providing insights into galaxy evolution post-merger.

Findings

Inverse correlation between core mass deficit and fine structure prominence.

Core depletion linked to SMBH binary activity during galaxy mergers.

Fine structures fade as the galaxy's gravitational potential relaxes.

Abstract

Deep exposure imaging of early-type galaxies (ETGs) are revealing the second-order complexity of these objects, which have been long considered uniform, dispersion-supported spheroidals. "Fine structure" features (e.g. ripples, plumes, tidal tails, rings) as well as depleted stellar cores (i.e. central light deficits) characterize a number of massive ETG galaxies, and can be interpreted as the result of galaxy-galaxy interactions. We discuss how the timescale for the evolution of cores and fine structures are comparable, and hence it is expected that they develop in parallel after the major interaction event which shaped the ETG. Using archival data, we compare the "depleted stellar mass" (i.e. the mass missing from the depleted stellar core) against the prominence of the fine structure features, and observe that they correlate inversely. This result confirms our expectation that, while the Super Massive Black Hole (SMBH) binary (constituted by the SMBHs of the merger progenitors) excavates the core via three-body interactions, the gravitational potential of the newborn galaxy relaxes, and the fine structures fade below detection levels. We expect the inverse correlation to hold at least within the first Gyr from the merger which created the SMBH binary; after then, the fine structure evolves independently.