Combining stellar populations with orbit-superposition dynamical modelling

the formation history of the lenticular galaxy NGC 3115

Adriano Poci, Richard M. McDermid, Ling Zhu, Glenn van de Ven

Research output: Contribution to journalArticle

6 Citations (Scopus)


We present a combination of the Schwarzschild orbit-superposition dynamical modelling technique with the spatially resolved mean stellar age and metallicity maps to uncover the formation history of galaxies. We apply this new approach to a remarkable five-pointing mosaic of VLT/MUSE observations obtained by Guérou et al. (2016) extending to a maximum galactocentric distance of ∼ 120, arcsec (5.6, kpc) along the major axis, corresponding to ∼2.5Re. Our method first identifies 'families' of orbits from the dynamical model that represent dynamically distinct structures of the galaxy. Individual ages and metallicities of these components are then fit for using the stellar-population information. Our results highlight components of the galaxy that are distinct in the combined stellar dynamics/populations space, which implies distinct formation paths. We find evidence for a dynamically cold, metal-rich disc, consistent with a gradual in situ formation. This disc is embedded in a generally old population of stars, with kinematics ranging from dispersion dominated in the centre to an old, diffuse, metal-poor stellar halo at the extremities. We find also a direct correlation between the dominant dynamical support of these components, and their associated age, akin to the relation observed in the Milky Way. This approach not only provides a powerful model for inferring the formation history of external galaxies but also paves the way to a complete population-dynamical model.

Original languageEnglish
Pages (from-to)3776-3796
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - Aug 2019


  • galaxies: elliptical and lenticular, cD
  • galaxies: individual: NGC 3115
  • galaxies: kinematics and dynamics
  • galaxies: stellar content
  • galaxies: structure

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