The impact of assembly bias on the halo occupation in hydrodynamical simulations

M. Celeste Artale, Idit Zehavi, Sergio Contreras, Peder Norberg

Research output: Contribution to journalArticlepeer-review

80 Citations (Scopus)


We investigate the variations in galaxy occupancy of the darkmatter haloes with the large-scale environment and halo formation time, using two state-of-the-art hydrodynamical cosmological simulations, EAGLE and Illustris. For both simulations, we use three galaxy samples with a fixed number density ranked by stellar mass. For these samples, we find that low-mass haloes in the most dense environments are more likely to host a central galaxy than those in the least dense environments. When splitting the halo population by formation time, these relations are stronger. Hence, at a fixed low halo mass, early-formed haloes are more likely to host a central galaxy than late-formed haloes since they have had more time to assemble. The satellite occupation shows a reverse trend where early-formed haloes host fewer satellites due to having more time to merge with the central galaxy. We also analyse the stellar mass-halo mass relation for central galaxies in terms of the large-scale environment and formation time of the haloes. We find that low-mass haloes in themost dense environment host relatively more massive central galaxies. This trend is also found when splitting the halo population by age, with early-formed haloes hosting more massive galaxies. Our results are in agreement with previous findings from semi-analytical models, providing robust predictions for the occupancy variation signature in the halo occupation distribution of galaxy formation models.

Original languageEnglish
Pages (from-to)3978-3992
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 2018
Externally publishedYes


  • Cosmology: theory
  • Galaxies: formation
  • Galaxies: haloes
  • Galaxies: statistics
  • Large-scale structure of Universe

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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