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Shapes, sizes, motion, etc.

16 - Galaxies. Shapes, sizes, motion, etc. Nature of the Spiral Nebulae and the Great Debate. 1920. Shapley Novae brightnesses incompatible with M31 being as big as MWG Rotation of M101. Curtis Novae indicate a smaller MWG than Shapley’s Galaxy proper motions undetected

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Shapes, sizes, motion, etc.

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  1. 16 - Galaxies Shapes, sizes, motion, etc.

  2. Nature of the Spiral Nebulae and the Great Debate 1920 Shapley • Novae brightnesses incompatible with M31 being as big as MWG • Rotation of M101 • Curtis • Novae indicate a smaller MWG than Shapley’s • Galaxy proper motions undetected • Zones of avoidance in other systems

  3. 1923 - Hubble Measures Distance to M 31 using Cepheid Variables

  4. Galaxy Classification (again) • Spirals: • Bulge/disk ratio • Tightness of spiral arms • Smoothness of spiral arms Ellipticals:

  5. S0, Sa, Sab, Sb, Sbc, Sc, Scd, Sd, Sdm, Sm, Im, Ir Parallel sequence (except for Ir) for Barred Spirals s = normal spiral arms r = “ring” galaxy

  6. S. Van den Bergh adds luminosity classes I, II, III, IV, V Morgan notes incompatibility of some of Hubble’s criteria and develops classification scheme using both shape and spectral type: a, af, f, fg, g, gk, k for net spectrum (stellar population) E,S,I (like Hubble) 0-10 for degree of flattening Not used today except for Diffuse galaxies with a central core - cD galaxies - the biggest galaxies in the universe!

  7. Origin of the Spiral Structure No One Really Knows!

  8. “Grand-Design” and “Flocculent” Arms (cloud-like “woolly”) M 51 - Grand-Design M 101 - Multiple Arm NGC 2841 - Flocculent

  9. The Problem of Wind-up For an galaxy with differential (i.e. not solid-body) rotation: If the arms are due entirely to current star density and no other forces are acting, the arms ought to “wind up”, giving them a short lifetime. The fraction of all disk galaxies with spiral arms is HUGE, indicating that the spiral structure has a long lifetime. So, this cannot be what is going on.

  10. General Instabilities?

  11. Spiral Density Waves

  12. This was resolved by Lin & Shu. Gas and stars are assumed to follow slightly elliptical orbits which are correlated. This arrangement produces a spiral density wave:

  13. “epicycle” Depending on the orbit/epicyclic ratio and offsets, one can get a variety of types:

  14. Animation by Michael Cowley

  15. Gas and stars orbit most of the time unperturbed on their elliptical orbits, but sometimes the orbits come close together and the density increases. So young stars , which define the arms most impressively, should lie downstream of the density wave. low density region low density region higher density region - the gas gets compressed and initiates star-formation

  16. 2-arm “grand-design” spirals

  17. Stochastic Self-Propagating Star Formation Young supernovae and OB star winds compress gas nearby, initiating a new round of star-formation. Differential galactic rotation shears the region into an elongated feature - spiral arm More important in flocculent-arm spirals?

  18. posted on YouTube by beltoforion1

  19. Driven Systems Passage of nearby galaxies causes a perturbation that produces a spiral arm (like M 51). Confirmed using n-body numerical simulations.

  20. The Tully-Fisher Relation 1. For a galaxies with flat rotation curves, it is possible to show that 2. If M/L is constant for galaxies (roughly true within a Hubble type): 3. Finally, if the surface brightness is the same (roughly true within a Hubble type) then:

  21. Note: • We measure Vrad, not V (need to correct for inclination) • Need to work within 1 Hubble class (or correct for differences due to type) • Near-IR wavelengths will be better, especially for high-inclination systems

  22. Elliptical Galaxies The Virgo Cluster - nearest rich cluster of galaxies See the maphere.Deep imagehere.

  23. M 87 (deep image here shows a jet – move cursor over image) M 86 M 89 Shapes due to velocity dispersion…..

  24. NGC 185 NGC 205 Dwarf Ellipticals - dE Dwarf Spheroidals - dSph Leo I

  25. Q: Is observed shape due to rotation or velocity dispersion? A: Yes. Geha et al. 2003, AJ, 126, 1794. Rotational Velocity & Velocity Dispersion in dE galaxies in Virgo Cluster

  26. galaxy spectrograph slit dE galaxies exhibiting net rotation

  27. Those with no rotation

  28. Ratio of vrot/σ

  29. Galaxy images before & after removal of “standard” elliptical intensity profiles

  30. The Local Group

  31. Spirals MWG M 31 M 33

  32. GCs in M31 Some GCs rotate with thin disk – RED is [Fe/H] < -2.0, BLUE is [Fe/H] > -2.0. Many younger than 5 Gyr, some only 0.1 Gyr?

  33. M31 Nucleus

  34. X-ray sources, including nuclear source (probably a black hole like MWG)

  35. NGC 205 M 32 Thisis a clickable atlas of the sky around M31, M32 and NGC 205. Sorry - seems to have vanished...

  36. Other Dwarf Ellipticals NGC 147 NGC 185

  37. Fornax Leo I Dwarf Spheroidals

  38. Sculptor Dwarf Spheroidal

  39. Dwarf Irregulars IC 10 NGC 6822 IC 1613

  40. WLM (Wolf-Lundmark-Melotte) H I vs. U U-B H II

  41. The Magellanic Clouds SMC LMC

  42. Supermassive Black Holes in the Local Group M32

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