The galaxy morphology-density relation in the EAGLE simulation

Abstract

The optical morphology of galaxies is strongly related to galactic environment, with the fraction of early-type galaxies increasing with local galaxy density. In this work we present the first analysis of the galaxy morphology-density relation in a cosmological hydrodynamical simulation. We use a convolutional neural network, trained on observed galaxies, to perform visual morphological classification of galaxies with stellar masses $M_{\ast }>10^{10}{\mathrm{M}}_{\odot }$ in the EAGLE simulation into elliptical, lenticular and late-type (spiral/irregular) classes. We find that EAGLE reproduces both the galaxy morphology-density and morphology-mass relations. Using the simulations, we find three key processes that result in the observed morphology-density relation: (i) transformation of disc-dominated galaxies from late-type (spiral) to lenticular galaxies through gas stripping in high-density environments, (ii) formation of lenticular galaxies by merger-induced black hole feedback in low-density environments, and (iii) an increasing fraction of high-mass galaxies, which are more often elliptical galaxies, at higher galactic densities.

19 pages, 17 figures, published in MNRAS

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• Deep Extragalactic VIsible Legacy Survey (DEVILS): First Data Release Covering The D10 (COSMOS) Region
• GalaxyGenius: Mock galaxy image generator for various telescopes from hydrodynamical simulations
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• Investigating the relation between environment and internal structure of massive elliptical galaxies using strong lensing
• Gamma Analytical Modeling Evolution (GAME) I: The physical implications of deriving the stellar mass functions from z=0 to z=8
• The Complex Structure of the Abell 548 - Abell 3367 Region