Galactic conformity measured in semi-analytic models

Ivan Lacerna, Sergio Contreras, Roberto E. González, Nelson Padilla, Violeta Gonzalez-Perez

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We study the correlation between the specific star formation rate of central galaxies and neighbour galaxies, also known as ‘galactic conformity’, out to 20 h−1Mpc using three semi-analytic models (SAMs, one from L-GALAXIES and other two from GALFORM). The aim is to establish whether SAMs are able to show galactic conformity using different models and selection criteria. In all the models, when the selection of primary galaxies is based on an isolation criterion in real space, the mean fraction of quenched (Q) galaxies around Q primary galaxies is higher than that around star-forming primary galaxies of the same stellar mass. The overall signal of conformity decreases when we remove satellites selected as primary galaxies, but the effect is much stronger in GALFORM models compared with the L-GALAXIES model. We find this difference is partially explained by the fact that in GALFORM once a galaxy becomes a satellite remains as such, whereas satellites can become centrals at a later time in L-GALAXIES. The signal of conformity decreases down to 60 per cent in the L-GALAXIES model after removing central galaxies that were ejected from their host halo in the past. Galactic conformity is also influenced by primary galaxies at fixed stellar mass that reside in dark matter haloes of different masses. Finally, we explore a proxy of conformity between distinct haloes. In this case, the conformity is weak beyond ∼3 h−1Mpc
(<3 per cent in L-GALAXIES, <1–2 per cent in GALFORM models). Therefore, it seems difficult that conformity is directly related with a long-range effect.
Original languageEnglish
Pages (from-to)1177-1189
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date20 Dec 2017
Publication statusPublished - 21 Mar 2018


  • astro-ph.GA
  • astro-ph.CO
  • galaxies: evoltion
  • galaxies: general
  • galaxies: haloes
  • galaxies: star formation
  • galaxies: statistics
  • RCUK
  • STFC
  • ST/M007995/1
  • ST/K00042X/1
  • ST/H008519/1
  • ST/K00087X/1
  • ST/K003267/1


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