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A Census of Compact Elliptical Galaxies in the Coma Cluster

Aleksandra V. Sharonova, Kirill A. Grishin, Igor V. Chilingarian, Gary A. Mamon, Nelson Caldwell, Daniel Fabricant

TL;DR

The paper investigates the origin of compact elliptical galaxies (cEs) in the Coma cluster, addressing whether they form directly in the cluster environment or are pre-processed in groups before infall. It combines deep HSC $g$-band imaging with spectroscopic data from DESI EDR and MMT Binospec to perform joint photometric and spectroscopic selection, expanding the known Coma cE population to 13 objects (7 previously known, 6 new). A subpopulation likely formed in infalling groups is identified via host associations, caustic diagram positions, and projected phase-space trajectories, highlighting pre-processing as a significant channel for cE evolution in the cluster. The authors project a $30\%$ increase in the central cE population within $0.4\ \mathrm{Gyr}$, underscoring the importance of group-processed pathways in shaping cluster CSS demographics.

Abstract

Compact elliptical (cE) galaxies are compact stellar systems with stellar masses of $10^8 \leq M_*/M_\odot \leq 10^{10}$ and radii typically < 0.6 kpc. Here we investigate the properties of 13 cE galaxies in the Coma cluster, six newly identified. Our goal in this paper is to explore whether these cEs form directly in the cluster environment or are pre-processed in small groups before infalling. We find that pre-processing in groups significantly contributes to the cE population in the Coma cluster. We analyze Hyper Suprime-Cam (HSC) g band Coma images and validate our photometric measurements through comparison with Hubble Space Telescope (HST) data. We also analyze spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI). We significantly expand the known cE population in the Coma cluster through joint photometric and spectroscopic selection. We identify a subpopulation of cEs that likely formed in infalling groups, through their association with host galaxies, their positions on the caustic diagram, and their projected phase-space trajectories. We estimate that the central cE population will increase by 30% within the next 0.4 Gyr, highlighting the important role of pre-processing in cE evolution.

A Census of Compact Elliptical Galaxies in the Coma Cluster

TL;DR

The paper investigates the origin of compact elliptical galaxies (cEs) in the Coma cluster, addressing whether they form directly in the cluster environment or are pre-processed in groups before infall. It combines deep HSC -band imaging with spectroscopic data from DESI EDR and MMT Binospec to perform joint photometric and spectroscopic selection, expanding the known Coma cE population to 13 objects (7 previously known, 6 new). A subpopulation likely formed in infalling groups is identified via host associations, caustic diagram positions, and projected phase-space trajectories, highlighting pre-processing as a significant channel for cE evolution in the cluster. The authors project a increase in the central cE population within , underscoring the importance of group-processed pathways in shaping cluster CSS demographics.

Abstract

Compact elliptical (cE) galaxies are compact stellar systems with stellar masses of and radii typically < 0.6 kpc. Here we investigate the properties of 13 cE galaxies in the Coma cluster, six newly identified. Our goal in this paper is to explore whether these cEs form directly in the cluster environment or are pre-processed in small groups before infalling. We find that pre-processing in groups significantly contributes to the cE population in the Coma cluster. We analyze Hyper Suprime-Cam (HSC) g band Coma images and validate our photometric measurements through comparison with Hubble Space Telescope (HST) data. We also analyze spectroscopic data from the Dark Energy Spectroscopic Instrument (DESI). We significantly expand the known cE population in the Coma cluster through joint photometric and spectroscopic selection. We identify a subpopulation of cEs that likely formed in infalling groups, through their association with host galaxies, their positions on the caustic diagram, and their projected phase-space trajectories. We estimate that the central cE population will increase by 30% within the next 0.4 Gyr, highlighting the important role of pre-processing in cE evolution.

Paper Structure

This paper contains 13 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Observational Data
  3. Hyper Suprime-Cam dataset
  4. DESI EDR spectra for Coma cluster
  5. MMT Binospec spectra
  6. Data Analysis
  7. Automated surface photometry with SourceXtractor++
  8. Analysis of DESI and Binospec spectra
  9. Results
  10. Search criteria of cEs and statistical properties of selected sample
  11. Photometric selection
  12. Spectroscopic selection of the Coma cluster members
  13. Photometric properties of cE galaxies

Figures (4)

  • Figure 1: The position of cE galaxies from our sample in the Coma cluster. Galaxies from 2009MNRAS.397.1816P are marked as pink squares and one galaxy from 2009Sci...326.1379C and 2009MNRAS.396.1647C is marked as red square.
  • Figure 2: Color-magnitude diagram for all Coma cluster members from DESI DR1, including cE galaxies described in the literature and galaxies from our sample.
  • Figure 3: Distribution of redshifts for galaxies that satisfy initial criteria plus $\mu_{\rm e,g}$ and $n$ constraints.
  • Figure 4: The size--luminosity 1977ApJ...218..333K and the surface brightness -- luminosity relations of early-type galaxies and compact stellar systems. cEs from our sample are shown by pink stars. The sources of other galaxies are shown in the legend below the plots. The grey filled areas and dashed lines denote the parameter space from Sec. \ref{['sec:ce_search']}.