Star Formation and Gas Alwin Mao March 21, 2019 10 2 1000 800 10 1 600 ( M pc Y (pc) 400 2 ) 10 0 200 0 10 1 0 200 400 600 800 1000 X (pc) Collaborators: Eve Ostriker, Chang-Goo Kim
Outline 1 Introduction: Efficiency of What Gas? 2 Time Series: Delay and Variability 3 Correlation Comparison of Density vs. Energy 4 Plans++ Alwin Mao Star Formation and Gas March 21, 2019 2 / 23
Outline 1 Introduction: Efficiency of What Gas? 2 Time Series: Delay and Variability 3 Correlation Comparison of Density vs. Energy 4 Plans++ Alwin Mao Star Formation and Gas March 21, 2019 3 / 23
Motivation - Efficiency per free-fall time M • SFR = ǫ ff t ff • ǫ ff ∼ 10 − 2 on galactic scales • ǫ ff ∼ 1 for bound collapsing objects? • ǫ ff ∝ e − β t dyn / t ff • β = 1 . 6 (Padoan, Haugbolle, and Nordlund 2012) • α v < 2? Alwin Mao Star Formation and Gas March 21, 2019 4 / 23
Motivation - TIGRESS • Athena MHD + self gravity + cooling/heating • Sink/star particles and supernova feedback • Galactic potential, kpc shearing box, tall box, pc resolution • Three-phase ISM in Galaxies Resolving Evolution with Star formation and Supernova feedback. Alwin Mao Star Formation and Gas March 21, 2019 5 / 23
Density Threshold 10 2 10 2 1000 800 10 1 10 1 600 ( M pc ( M pc Y (pc) 400 2 ) 2 ) 10 0 10 0 200 0 10 10 1 1 0 200 400 600 800 1000 X (pc) Alwin Mao Star Formation and Gas March 21, 2019 6 / 23
Gravitational Energy - Isocontour Alwin Mao Star Formation and Gas March 21, 2019 7 / 23
Grav. Energy - Well AB AB ab A B A B b ab ab a b a Alwin Mao Star Formation and Gas March 21, 2019 8 / 23
Grav. Energy - Tree Example 10 2 1000 411 240 800 250 10 1 260 600 ( M pc Y (pc) 270 280 400 2 ) 10 0 290 300 200 310 320 0 10 1 0 200 400 600 800 1000 0 10 20 30 40 50 60 X (pc) Tree Index Alwin Mao Star Formation and Gas March 21, 2019 9 / 23
Grav. Energy - Tree (Merged Example) 555 780 790 800 810 820 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 Tree Index Alwin Mao Star Formation and Gas March 21, 2019 10 / 23
Grav. Energy - Movie 10 2 1000 800 10 1 600 ( M pc Y (pc) 400 2 ) 10 0 200 0 10 1 0 200 400 600 800 1000 X (pc) Alwin Mao Star Formation and Gas March 21, 2019 11 / 23
Outline 1 Introduction: Efficiency of What Gas? 2 Time Series: Delay and Variability 3 Correlation Comparison of Density vs. Energy 4 Plans++ Alwin Mao Star Formation and Gas March 21, 2019 12 / 23
Time Series - Density SFR density bin delayed 10 1 10 0.5 0 cm 3 n H 10 0 10 1 ff (Mass / t ff ) / <SFR> 10 1 10 0 0.5 cm 3 n H 10 0 10 1 10 1 10 0.5 1 cm 3 n H 10 0 10 1 300 350 400 450 500 550 600 650 700 Time (Myr) Alwin Mao Star Formation and Gas March 21, 2019 13 / 23
Time Series - High Density SFR density bin delayed 10 1 10 1 1.5 cm 3 n H 10 0 10 1 ff (Mass / t ff ) / <SFR> 10 1 10 1.5 2 cm 3 n H 10 0 10 1 10 1 10 2 2.5 cm 3 n H 10 0 10 1 300 350 400 450 500 550 600 650 700 Time (Myr) Alwin Mao Star Formation and Gas March 21, 2019 14 / 23
Time Series - Density Time Delay Time Series t ff, min t ff, max Time (Myr) 10 1 10 1 10 2 n H, min (cm 3 ) Alwin Mao Star Formation and Gas March 21, 2019 15 / 23
Time Series - Energy-selected SFR density bin delayed 10 1 HBR ff (Mass / t ff ) / <SFR> 10 0 10 1 10 1 HBP 10 0 10 1 300 350 400 450 500 550 600 650 700 Time (Myr) Alwin Mao Star Formation and Gas March 21, 2019 16 / 23
Outline 1 Introduction: Efficiency of What Gas? 2 Time Series: Delay and Variability 3 Correlation Comparison of Density vs. Energy 4 Plans++ Alwin Mao Star Formation and Gas March 21, 2019 17 / 23
Correlation - Constant ǫ ff Model between 10 − 2 − 1 10 0 1.0 0.8 SFR / < SFR > 0.6 10 1 ff 0.4 0.2 10 2 0.0 n H > 10 n H > 30 n H > 100 HBR n H > 10 n H > 30 n H > 100 HBR Alwin Mao Star Formation and Gas March 21, 2019 18 / 23
Correlation - ǫ ff ∝ e − β t dyn / t ff Model 2.0 1.0 1.5 0.8 1.0 SFR / < SFR > 0.6 0.5 0.4 0.0 0.2 0.5 1.0 0.0 n H > 10 n H > 30 n H > 100 HBR n H > 10 n H > 30 n H > 100 HBR Alwin Mao Star Formation and Gas March 21, 2019 19 / 23
Correlation - α v < Cutoff α v Model 9 1.0 8 0.8 7 6 SFR / < SFR > 0.6 v 5 Cutoff 4 0.4 3 2 0.2 1 0 0.0 n H > 10 n H > 30 n H > 100 HBR n H > 10 n H > 30 n H > 100 HBR Alwin Mao Star Formation and Gas March 21, 2019 20 / 23
Outline 1 Introduction: Efficiency of What Gas? 2 Time Series: Delay and Variability 3 Correlation Comparison of Density vs. Energy 4 Plans++ Alwin Mao Star Formation and Gas March 21, 2019 21 / 23
Plans++ • Form stellar cores in turbulent boxes in dense (100-10000 cm − 3 ) gas • Compare various Lagrangian Tracer Particle implementations • Figure out ways to distill understanding Alwin Mao Star Formation and Gas March 21, 2019 22 / 23
Conclusions • Time delay ≈ t ff • ǫ ff depends on gas selection • More sophisticated energy-based selection not necessarily closer to SFR • Most mass is unbound, and does not stay bound for long (few Myr) • Unbound objects are involved in star formation Alwin Mao Star Formation and Gas March 21, 2019 23 / 23
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