Chaos and stellar streams

Dissertation talk presented at the American Astronomical Society winter meeting 2016 (AAS 227).

Transcript

1. CHAOS Stellar Streams Adrian Price-Whelan + K. V. Johnston, M. Valluri, S. Pearson, A. H. W. Küpper, D. W. Hogg, B. Sesar, H-W Rix (Columbia University) adrn ! adrianprw "
2. Stellar streams and tidal debris Milky Way: ~20 known, large range in distance and mass Bonaca, Giguere, Geha
3. Stellar streams and tidal debris Milky Way: ~20 known, large range in distance and mass Bonaca, Giguere, Geha (globular?) (globular)
4. Stellar streams and tidal debris Milky Way: ~20 known, large range in distance and mass Bonaca, Giguere, Geha (globular?) (globular) (dwarf Gal) (dwarf Gal?)
5. 1. Dark matter halo properties 2. Accretion histories 3. Formation of stellar halos Stellar streams and tidal debris Thesis work: Connecting galaxies to cosmology
6. 1. Dark matter halo properties 2. Accretion histories 3. Formation of stellar halos Stellar streams and tidal debris Thesis work: Connecting galaxies to cosmology - Shape / triaxiality? Mass profile? (Price-Whelan et al. 2013, 2014, 2016)
7. 1. Dark matter halo properties 2. Accretion histories 3. Formation of stellar halos Stellar streams and tidal debris Thesis work: Connecting galaxies to cosmology - How many accreted? When? Orbits? Masses, etc.? (Price-Whelan et al. 2016) - Shape / triaxiality? Mass profile? (Price-Whelan et al. 2013, 2014, 2016)
8. 1. Dark matter halo properties 2. Accretion histories 3. Formation of stellar halos Stellar streams and tidal debris Thesis work: Connecting galaxies to cosmology - All accreted? Kicked out of disk? Formed in situ? (Price-Whelan et al. 2015) - How many accreted? When? Orbits? Masses, etc.? (Price-Whelan et al. 2016) - Shape / triaxiality? Mass profile? (Price-Whelan et al. 2013, 2014, 2016)
9. • Predictions for dark matter halo shapes • Implications for stream evolution • Modeling a stream to study the Galactic bar Outline DM halo properties affect stream morphology
10. (Caterpillar simulations; Griffen et al. 2015) Simulated dark matter halos
11. (Caterpillar simulations; Griffen et al. 2015) Simulated dark matter halos
12. Simulated dark matter halos Milky Way-mass halos are strongly triaxial (Millennium-II; Schneider et al. 2012) pdf 0.2 0.4 0.6 0.8 1.0 0.0 (c/a) (b/a) Axis ratio in density
13. Orbits in triaxial systems Regular motion 3 integrals of motion 3 fundamental frequencies, O (⌦1, ⌦2, ⌦3) x ( t ) = 1 X k ak e i !k t motion in any component:
14. Orbits in triaxial systems Regular motion 3 integrals of motion 3 fundamental frequencies, O (⌦1, ⌦2, ⌦3) x ( t ) = 1 X k ak e i !k t !k = n1⌦1 + n2⌦2 + n3⌦3 (for integers n) motion in any component:
15. Orbits in triaxial systems Regular motion 3 integrals of motion 3 fundamental frequencies, O Chaotic motion only conserve energy frequencies evolve with time (⌦1, ⌦2, ⌦3) x ( t ) = 1 X k ak e i !k t !k = n1⌦1 + n2⌦2 + n3⌦3 (for integers n) motion in any component:
16. x(t) time time Orbits in triaxial systems Regular motion 3 fundamental frequencies, O Chaotic motion frequencies evolve with time (⌦1, ⌦2, ⌦3) x(t)
17. FFT frequency frequency FFT Orbits in triaxial systems Regular motion Chaotic motion 3 fundamental frequencies, O frequencies evolve with time (⌦1, ⌦2, ⌦3) wk
18. window 1 window 2 e.g., Valluri & Merritt (1998) Frequency diffusion time
19. window 1 window 2 e.g., Valluri & Merritt (1998) ⌦w1 ⌦w2 Frequency diffusion time
20. window 1 window 2 e.g., Valluri & Merritt (1998) ⌦w1 ⌦w2 T Frequency diffusion time
21. Triaxial NFW b/a = 0.77 c/a = 0.55 }in density Static triaxial potential model
22. Frequency diffusion time Price-Whelan et al. (2016) more chaotic less chaotic
23. Frequency diffusion time Long-axis tube Short- axis tube Box ZVC (Box) Price-Whelan et al. (2016) more chaotic less chaotic
24. 104 M Progenitor mass = Star particle positions after 10 Gyr Price-Whelan et al. (2016) x y y z 20 kpc Streams in triaxial systems Regular orbits
25. Stream star frequencies relative to progenitor orbit Price-Whelan et al. (2016) 2% ⌦1 ⌦2 ⌦3 ⌦2 Streams in triaxial systems Regular orbits
26. Stream star frequencies relative to progenitor orbit Price-Whelan et al. (2016) 2% ⌦1 ⌦2 ⌦3 ⌦2 Streams in triaxial systems Regular orbits 1 > 2 > 3 1 2 3
27. 2% ⌦1 ⌦2 ⌦3 ⌦2 Frequencies relative to progenitor Price-Whelan et al. (2016) Streams in triaxial systems Chaotic orbits ⌦2 ⌦3 Weak chaos: Strong chaos:
28. Star particle positions after 10 Gyr Price-Whelan et al. (2016) x y y z Streams in triaxial systems Chaotic orbits y z 20 kpc Weak chaos: Strong chaos:
29. Price-Whelan et al. (2016) Dark matter halos are expected to be triaxial Chaotic orbits are prevalent in triaxial systems Streams affected by chaos disperse faster: Form low density “fans” with large velocity dispersion Conclusions
30. In the Milky Way radius-dependent axis ratios time-dependence (e.g., mass growth) subhalos disk, bulge, bar Triaxiality PLUS:
31. Thin streams exist around the Milky Way! Bonaca, Giguere, Geha
32. Implications Connecting galaxies to cosmology 1. Dark matter halo properties Do the known thin streams map the regular orbits? Is the MW potential more regular?
33. Implications Connecting galaxies to cosmology 1. Dark matter halo properties Do the known thin streams map the regular orbits? Is the MW potential more regular? 2. Accretion histories Measuring dynamical age / accretion time difficult if stream is chaotic
34. Implications Connecting galaxies to cosmology 1. Dark matter halo properties Do the known thin streams map the regular orbits? Is the MW potential more regular? 2. Accretion histories Measuring dynamical age / accretion time difficult if stream is chaotic 3. Formation of stellar halos Substructure smoothed out by chaos — less halo substructure in Gaia?
35. Blue Horizontal Branch stars The Ophiuchus Stream Sesar et al. (2015) Bernard et al. (2014) Short: 2º, 1.5 kpc Age: ~10–12 Gyr (R,z) ~ (1,4) kpc Orbital period: ~400 Myr but… l [deg] v los [km/s] b [deg] 4 5 6 30 31 32 294 290 286 282
36. Blue Horizontal Branch stars The Ophiuchus Stream Sesar et al. (2015) Bernard et al. (2014) Short: 2º, 1.5 kpc Age: ~10–12 Gyr (R,z) ~ (1,4) kpc Orbital period: ~400 Myr but… l [deg] v los [km/s] b [deg] 4 5 6 30 31 32 294 290 286 282 Kicked on to this orbit, full disruption ~300 Myr ago?
37. l [deg] v los [km/s] b [deg] 4 5 6 30 31 32 294 290 286 282 Sesar, Price-Whelan et al. (2016) l [deg] Blue Horizontal Branch stars The Ophiuchus Stream Sesar et al. (2015) Bernard et al. (2014)
38. l [deg] v los [km/s] b [deg] 4 5 6 30 31 32 294 290 286 282 Sesar, Price-Whelan et al. (2016) l [deg] Blue Horizontal Branch stars The Ophiuchus Stream Sesar et al. (2015) Bernard et al. (2014)
39. Sesar, Price-Whelan et al. (2016) l [deg] The Ophiuchus Stream Sesar et al. (2015) Bernard et al. (2014) 6 of all 40 BHB stars in this field are consistent in distance, sky position 4 of those 6 w/ large velocity dispersion
40. + Galactic Bar The Ophiuchus Stream On a chaotic orbit? Price-Whelan et al. (in prep.) Static, Axisymmetric
41. The Ophiuchus Stream Consistent with chaotic stream fanning (nearby low-density debris with large dispersion?) Sensitive to the potential of the Milky Way bar (independent measure of pattern speed, mass)