The formation pathways of compact elliptical galaxies

Abstract

Compact elliptical (cE) galaxies remain an elusively difficult galaxy class to study. Recent observations have suggested that isolated and host-associated cEs have different formation pathways, while simulation studies have also shown different pathways can lead to a cE galaxy. However a solid link has not been established, and the relative contributions of each pathway in a cosmological context remains unknown. Here we combine a spatially-resolved observational sample of cEs taken from the SAMI galaxy survey with a matched sample of galaxies within the IllustrisTNG cosmological simulation to establish an overall picture of how these galaxies form. The observed cEs located near a host galaxy appear redder, smaller and older than isolated cEs, supporting previous evidence for multiple formation pathways. Tracing the simulated cEs back through time, we find two main formation pathways; 32 $\pm$ 5 percent formed via the stripping of a spiral galaxy by a larger host galaxy, while 68 $\pm$ 4 percent formed through a gradual build-up of stellar mass in isolated environments. We confirm that cEs in different environments do indeed form via different pathways, with all isolated cEs in our sample having formed via in-situ formation (i.e. none were ejected from a previous host), and 77 $\pm$ 6 percent of host-associated cEs having formed via tidal stripping. Separating them by their formation pathway, we are able to reproduce the observed differences between isolated and host-associated cEs, showing that these differences can be fully explained by the different formation pathways dominating in each environment.

18 pages, 15 figures, accepted for publication in MNRAS. Corrected Table 1

References in corpus (31)

• Compaction and Quenching of High-z Galaxies in Cosmological Simulations: Blue and Red Nuggets
• The SAMI Galaxy Survey: instrument specification and target selection
• SKIRT: an Advanced Dust Radiative Transfer Code with a User-Friendly Architecture
• The AIMSS Project I: Bridging the Star Cluster - Galaxy Divide
• The SAMI Galaxy Survey: the link between angular momentum and optical morphology
• The SAMI Galaxy Survey: Revisiting Galaxy Classification Through High-Order Stellar Kinematics
• The SAMI Galaxy Survey: Early Data Release
• The SAMI Galaxy Survey: the third and final data release
• The SAMI Galaxy Survey: Spatially Resolving the Main Sequence of Star Formation
• The SAMI Galaxy Survey: Cubism and covariance, putting round pegs into square holes
• Hiding in plain sight: An abundance of compact massive spheroids in the local Universe
• On the Origin of Dwarf Elliptical Galaxies: The Fundamental Plane
• The Next Generation Virgo Cluster Survey. XII. Stellar Populations and Kinematics of Compact, Low-Mass Early-Type Galaxies from Gemini GMOS-IFU Spectroscopy
• The Fornax Deep Survey (FDS) with the VST XI. The search for signs of preprocessing between the Fornax main cluster and Fornax A group
• The CALIFA view on stellar angular momentum across the Hubble sequence
• The formation of UCDs and massive GCs: Quasar-like objects for testing for a variable stellar initial mass function (IMF)
• Isolated compact elliptical galaxies: Stellar systems that ran away
• The two formation pathways of S0 galaxies
• Convergence properties of halo merger trees; halo and substructure merger rates across cosmic history
• The SAMI -- Fornax Dwarfs Survey I: Sample, observations and the specific stellar angular momentum of dwarf elliptical galaxies
• The SAMI Galaxy Survey: Physical drivers of stellar-gas kinematic misalignments in the nearby Universe
• On the formation mechanisms of compact elliptical galaxies
• Tidal Interaction as the origin of early-type dwarf galaxies in group environment
• Prospects for Recovering Galaxy Intrinsic Shapes from Projected Quantities
• Low-mass compact elliptical galaxies: spatially-resolved stellar populations and kinematics with the Keck Cosmic Web Imager
• Two channels for the formation of compact dwarf galaxies in clusters of galaxies
• Physical properties of compact star-forming galaxies at $z\sim 2-3$
• Contribution of stripped nuclei to the ultracompact dwarf galaxy population in the Virgo Cluster
• Discovery of a Bimodal Environmental Distribution of Compact Ellipticals in the Local Universe
• M32 Analogs? A Population of Massive Ultra Compact Dwarf and Compact Elliptical Galaxies in intermediate redshift CLASH Clusters
• Compact elliptical galaxies hosting active galactic nuclei in isolated environment

Cited by in corpus (1)

• Formation of Transitional cE/UCD Galaxies through Massive/Dwarf Disc Galaxy Mergers