M32 Analogs? A Population of Massive Ultra Compact Dwarf and Compact Elliptical Galaxies in intermediate redshift CLASH Clusters

TL;DR

This study identifies a population of massive ultra compact dwarf and compact elliptical galaxy candidates in intermediate redshift galaxy clusters, suggesting they may originate from tidal stripping or early formation, and demonstrates the potential of large imaging surveys for their statistical analysis.

Contribution

First identification of M32-like UCD and CE candidates in intermediate redshift clusters using CLASH survey data, highlighting their properties and possible origins.

Findings

Average of 2.7 such objects per cluster within 0.3 Mpc

More than half have radii smaller than 200 pc

Properties consistent with tidal stripping origin

Abstract

We report the discovery of relatively massive, M32-like ultra compact dwarf (UCD) and compact elliptical (CE) galaxy candidates in $0.2<z<0.6$ massive galaxy clusters imaged by the Cluster Lensing And Supernova survey with {\it Hubble} (CLASH) survey. Examining the nearly unresolved objects in the survey, we identify a sample of compact objects concentrated around the cluster central galaxies with colors similar to cluster red sequence galaxies. Their colors and magnitudes suggest stellar masses around $10^9 \mathrm{M_{\odot}}$. More than half of these galaxies have half-light radii smaller than 200 pc, falling into the category of massive UCDs and CEs, with properties similar to M32. The properties are consistent with a tidal stripping origin, but we cannot rule out the possibility that they are early-formed compact objects trapped in massive dark matter halos. The 17 CLASH clusters studied in this work on average contain 2.7 of these objects in their central 0.3 Mpc and 0.6 in their central 50 kpc. Our study demonstrates the possibility of statistically characterizing UCDs/CEs with a large set of uniform imaging survey data.