First light and reionisation epoch simulations (FLARES) - VIII. The emergence of passive galaxies at z ≥ 5

Christopher C. Lovell*, Will Roper, Aswin P. Vijayan, Louise Seeyave, Dimitrios Irodotou, Stephen M. Wilkins, Christopher J. Conselice, Flaminia Fortuni, Jussi K. Kuusisto, Emiliano Merlin, Paola Santini, Peter Thomas

*Corresponding author for this work

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Abstract

Passive galaxies are ubiquitous in the local universe, and various physical channels have been proposed that lead to this passivity. To date, robust passive galaxy candidates have been detected up to z ≤ 5, but it is still unknown if they exist at higher redshifts, what their relative abundances are, and what causes them to stop forming stars. We present predictions from the first light and reionisation epoch simulations (flares), a series of zoom simulations of a range of overdensities using the eagle code. Passive galaxies occur naturally in the eagle model at high redshift, and are in good agreement with number density estimates from Hubble Space Telescope (HST) and early JWST results at 3 ≤ z ≤ 5. Due to the unique flares approach, we extend these predictions to higher redshifts, finding passive galaxy populations up to z ∼ 8. Feedback from supermassive black holes is the main driver of passivity, leading to reduced gas fractions and star forming gas reservoirs. We find that passive galaxies at z ≥ 5 are not identified in the typical UVJ selection space due to their still relatively young stellar populations, and present new rest-frame selection regions. We also produce mock NIRCam and MIRI fluxes, and find that significant numbers of passive galaxies at z ≥ 5 should be detectable in upcoming wide surveys with JWST. Finally, we present JWST colour distributions, with new selection regions in the observer–frame for identifying these early passive populations.

Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Volume525
Issue number4
Pages (from-to)5520-5539
ISSN0035-8711
DOIs
Publication statusPublished - 2023

Keywords

  • Galaxies: abundances
  • Galaxies: high-redshift
  • Galaxies: photometry
  • Methods: numerical

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