Great balls of FIRE - I. The formation of star clusters across cosmic time in a Milky Way-mass galaxy

Michael Y. Grudić*, Zachary Hafen, Carl L. Rodriguez, Dávid Guszejnov, Astrid Lamberts, Andrew Wetzel, Michael Boylan-Kolchin, Claude Andre Faucher-Giguère

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


The properties of young star clusters formed within a galaxy are thought to vary in different interstellar medium conditions, but the details of this mapping from galactic to cluster scales are poorly understood due to the large dynamic range involved in galaxy and star cluster formation. We introduce a new method for modelling cluster formation in galaxy simulations: mapping giant molecular clouds (GMCs) formed self-consistently in a FIRE-2 magnetohydrodynamic galaxy simulation on to a cluster population according to a GMC-scale cluster formation model calibrated to higher resolution simulations, obtaining detailed properties of the galaxy's star clusters in mass, metallicity, space, and time. We find ∼ 10 per cent of all stars formed in the galaxy originate in gravitationally bound clusters overall, and this fraction increases in regions with elevated ςgas and ςSFR, because such regions host denser GMCs with higher star formation efficiency. These quantities vary systematically over the history of the galaxy, driving variations in cluster formation. The mass function of bound clusters varies - no single Schechter-like or power-law distribution applies at all times. In the most extreme episodes, clusters as massive as 7 × 106 M⊙ form in massive, dense clouds with high star formation efficiency. The initial mass-radius relation of young star clusters is consistent with an environmentally dependent 3D density that increases with ςgas and ςSFR. The model does not reproduce the age and metallicity statistics of old (> 11 Gyr) globular clusters found in the Milky Way, possibly because it forms stars more slowly at z > 3.

Original languageEnglish (US)
Pages (from-to)1366-1380
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - Feb 1 2023


  • ISM: clouds
  • galaxies: star clusters: general
  • galaxies: star formation
  • globular clusters: general
  • open clusters and associations: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Great balls of FIRE - I. The formation of star clusters across cosmic time in a Milky Way-mass galaxy'. Together they form a unique fingerprint.

Cite this