Star clusters without the stars: FIRE at small scales Mike Grudi - - PowerPoint PPT Presentation

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Star clusters without the stars: FIRE at small scales Mike Grudi - - PowerPoint PPT Presentation

Feb 04, 2024 173 likes •339 views

Star clusters without the stars: FIRE at small scales Mike Grudi Caltech GalFRESCA 2017 FIRE Simulations Wetzel 2016 Simulate galaxy formation with explicitly-resolved ISM physics Trend toward finer mass resolutions: -

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Star clusters without the stars: FIRE at small scales

Mike Grudić Caltech GalFRESCA 2017

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FIRE Simulations


 Wetzel 2016

  • Simulate galaxy formation with explicitly-resolved ISM physics
  • Trend toward finer mass resolutions:
  • MW-like galaxies: Mbaryon = 880M☉
  • Dwarf galaxies: Mbaryon = 30M☉ (!!!)

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How predictive is FIRE at such small scales?

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Star formation without the stars

Fragmentation resolved Fragmentation unresolved

LJeans(ρ1,T1,vturb,1)

Turn into “star particle” within ~tff

LJeans(ρ2,T2,vturb,2)

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Numerical Experiments

Grudić et al. 2016 arXiv:1612.05635

  • Isolated cloud

collapse parameter study:

  • Σ~102-104 M☉pc-2

R~5-500pc

  • SFE~1-70%
  • Laboratory for GMC

and cluster formation

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Sanity Check 1: Linewidth- Size Relation

Observations: GMCs obey 𝜏v ∝ R0.5 (Larson 1981, Bolatto 2008) Bolatto 2008

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Sanity Check 1: Linewidth- Size Relation

Grudić 2016 simulations:

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Sanity Check 2: Stellar Correlation Function

Guszejnov, Hopkins and Grudić 2017: arXiv:1707.05799 Observations: ξ2D ∝ R-1 in nascent star clusters (ξ3D ∝ R-2)

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Sanity Check 2: Stellar Correlation Function

Guszejnov, Hopkins and Grudić 2017: arXiv:1707.05799

Simulations:

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Sanity Check 3: Star Cluster Structure

Observation: young massive clusters generally fit by Elson 1987 surface density model: Elson, Fall, and Freeman 1987

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Sanity Check 3: Star Cluster Structure

Simulations:

  • Star clusters that form are also very well-fit by EFF model

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Sanity Check 3: Star Cluster Structure

  • Distribution of surface brightness slopes matches observations
  • Star cluster structure emerges from hierarchical assembly

(Grudić et al. 2017, check arXiv next week!)

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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 Grudić 2017) Adaptive physics methods capture scale-free structure formation

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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.

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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

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Bonus: GMC simulation with M1 RHD tracking FIR/NIR/OPT/UV (Preliminary)

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