Star clusters without the stars: FIRE at small scales Mike Grudi ć Caltech GalFRESCA 2017
FIRE Simulations Wetzel 2016 • Simulate galaxy formation with explicitly-resolved ISM physics • Trend toward finer mass resolutions: - MW-like galaxies: M baryon = 880M ☉ - Dwarf galaxies: M baryon = 30M ☉ (!!!) How predictive is FIRE at such small scales? 2
Star formation without the stars L Jeans ( ρ 1 ,T 1 ,v turb,1 ) L Jeans ( ρ 2 ,T 2 ,v turb,2 ) Fragmentation Fragmentation Turn into “star resolved unresolved particle” within ~t ff 3
Numerical Experiments • Isolated cloud collapse parameter study: • Σ ~10 2 -10 4 M ☉ pc -2 R~5-500pc • SFE~1-70% • Laboratory for GMC and cluster formation Grudi ć et al. 2016 arXiv:1612.05635 4
Sanity Check 1: Linewidth- Size Relation Observations: GMCs obey 𝜏 v ∝ R 0.5 (Larson 1981, Bolatto 2008) 5 Bolatto 2008
Sanity Check 1: Linewidth- Size Relation Grudi ć 2016 simulations : 6
Sanity Check 2: Stellar Correlation Function Observations: ξ 2D ∝ R -1 in nascent star clusters ( ξ 3D ∝ R -2 ) Guszejnov, Hopkins and Grudi ć 2017: arXiv:1707.05799 7
Sanity Check 2: Stellar Correlation Function Simulations: Guszejnov, Hopkins and Grudi ć 2017: arXiv:1707.05799 8
Sanity Check 3: Star Cluster Structure Observation: young massive clusters generally fit by Elson 1987 surface density model: Elson, Fall, and Freeman 1987 9
Sanity Check 3: Star Cluster Structure Simulations: • Star clusters that form are also very well-fit by EFF model 10
Sanity Check 3: Star Cluster Structure • Distribution of surface brightness slopes matches observations • Star cluster structure emerges from hierarchical assembly (Grudi ć et al. 2017, check arXiv next week!) 11
Why does it work? •ISM structure and kinematics emerge naturally from gravity + ~isothermal supersonic turbulence •Isothermal MHD+gravity are approximately scale-free: (Guszejnov, Hopkins and Grudi ć 2017) Adaptive physics methods capture scale-free structure formation 12
Summary Simulated GMCs and star clusters with FIRE pass the duck test : • Looks like a duck • Swims like a duck • Quacks like a duck • Is not a duck, but can still help us understand the phenomenology of ducks. 13
Actual Summary • Properties of GMCs and star clusters emerge from scale-free physics of gravity + supersonic turbulence, so adaptive physics methods are essential. • At sufficiently high resolution, FIRE physics will predict: - Resolved GMC properties - Formation and structure of massive star clusters • One killer app: high-z globular cluster formation e.g. Kim et al. 2017 arXiv:1704.02988 14
Bonus: GMC simulation with M1 RHD tracking FIR/NIR/OPT/UV (Preliminary) 15
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