Different Origins of Nucleated and Non-nucleated Dwarf Elliptical Galaxies: Identified by the Deep-learning

TL;DR

This study uses deep learning to classify and analyze the spatial distribution of nucleated and non-nucleated dwarf elliptical galaxies in the Virgo cluster, revealing different formation histories.

Contribution

It introduces a machine learning framework to classify a large sample of dEs and uncovers their distinct spatial distributions and origins within the cluster.

Findings

Nucleated dEs are more clustered and associated with massive galaxies.

Non-nucleated dEs are more dispersed and aligned with the cluster's potential well.

Different origins for nucleated and non-nucleated dEs are suggested.

Abstract

Dwarf elliptical galaxies (dEs) are the dominant population in galaxy clusters and serve as ideal probes for studying the environmental impact on galactic evolution. A substantial fraction of dEs are known to harbor central nuclei, which are among the densest stellar systems in the Universe. The large-scale distribution and the underlying origin of nucleated and non-nucleated dEs remain unresolved. Using a state-of-the-art machine learning framework, we systematically scan the Virgo cluster region ($15\arcdeg \times 20\arcdeg$ centered at $R.A. = 187.2\arcdeg$ and $Dec. = 9.6\arcdeg$) and construct the largest homogeneous sample of dEs (of total 2,123) with robust nucleus classifications. We find that nucleated dEs are more spatially clustered and exhibit a stronger association with massive galaxies than their non-nucleated counterparts. This suggests that most nucleated dEs likely formed alongside massive galaxies within the cluster (i.e, the in-situ formation). In contrast, non-nucleated dEs are more widely distributed across the cluster and align more closely with Virgo's global potential well, as traced by the cluster's hot gas. This indicates that most non-nucleated dEs originated outside the cluster (i.e, the ex-situ formation) and were later accreted and redistributed within it. Our findings shed new light on how dEs and their central nuclei form and evolve.