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AY16 March 20, 2008 Galaxies

AY16 March 20, 2008 Galaxies. Galaxies. A modern topic: 1920 Shapley-Curtis Debate Evidence against galaxies as external 1. Proper motion of M31 (van Maanen) 2. Shapley’s GC Distances 3. “Nova” 1885a in M31 Killer evidence for:

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AY16 March 20, 2008 Galaxies

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  1. AY16March 20, 2008 Galaxies

  2. Galaxies A modern topic: 1920 Shapley-Curtis Debate Evidence against galaxies as external 1. Proper motion of M31 (van Maanen) 2. Shapley’s GC Distances 3. “Nova” 1885a in M31 Killer evidence for: 1. Hubble’s discovery of Cepheids in 3 galaxies and their distance determinations.

  3. What Are Galaxies? • Artifacts of the Formation Process • Tracers of Test Particles of Larger Dynamics • Froth on an Ocean of Dark Matter • Objects Deserving Detailed Study in Their Own Right

  4. We hold these truths … Galaxies have a broad range of properties There exist connections between these properties and other parameters (location, location, location ---- formation + evolution) We must understand these connections to use galaxies to understand the cosmological model.

  5. Morphology Hubble’s Tuning Fork Sa Sb Sc Sd S0 Irr E0 E6 SB0 Ellipticity = 10(a-b)/a < ~ 7 observationally SBa SBb SBc SBd

  6. Irregular Galaxies LMC = IBm M82 = Irr II = I0

  7. Morphological classification is just taking the grossest, simplest observational properties and moving the bins around until they make sense. Relate form to physics. Regarding S0 galaxies, Hubble said “at present, the suggestion of cataclysmic action at this critical point in the evolutional development of nebulae is rather pronounced.” Hubble thought his diagram was an evolutionary sequence!

  8. Hubble Types are now (1) Not considered to be “evolutionary” (2) Considerably Embellished! by Sandage, deVaucouleurs, van den Bergh, ++ • Irr  Im plus I0 • Sub classes added Sa, Sab, Sb, Sbc, Sc, Scd, Sd, Sdm, Sm, Im and S0/a = slight signs of structure in the disk (3) S0 class well established + rings, mixed types and peculiarities

  9. e.g. SAbc(r) p = open Sbc galaxy with an inner ring and some peculiarities SX(rs)0 = mixed S0 galaxy with mixed ring morphology SBdm = barred very late type spiral galaxy

  10. deVaucouleurs Expansion

  11. Other Embellishments S. Van den Bergh introduced luminosity classes in the 1960’s  for spirals, L is a function of appearance. I = giant ---- V = dwarf this was used for a while to estimate H0. (ugh!) in the 1970’s he introduced the Anemic sequence: very low surface brightness disks which is probably connected to the “stripping” of spirals in the field

  12. Discovery of Anemic spirals and other effects (e.g. the morphology-density relation) spawned the “Nature” vs “Nurture” debate: Are S0’s born or made? Do field S0’s exist? Morgan in the 1950’s introduced spectral types for galaxies a, af, f, fg, g, gk, k which never caught on (but E+A galaxies are now a hot topic – emission + A type)

  13. Finally, in the 1960’s the search for active galaxies and radio galaxies caused Morgan to introduce another classification scheme D galaxies --- E galaxies with apparently extended envelopes. cD galaxies --- Centrally located D’s N galaxies --- Compact Nuclei Plus other types like Seyferts + LINERS (both specroscopic) and Zwicky’s compact and “post-eruptive” galaxies…

  14. M81 3.6μ

  15. M81 Spitzer 3.6, 8.0 + 24 μ

  16. M87

  17. M87 Deep AAT USM

  18. 2 μ

  19. M101 W. Keel Optical

  20. M101 UIT

  21. R. Gendler

  22. Ring galaxy

  23. Crashing galaxies = The Antennae

  24. Arp Introduced Peculiar Galaxies (1966) Atlas of Peculiar Galaxies, mostly interacting. Some 30% of al NGC objects are in the Arp or Vorontsov-Velyaminov catalogs. (Arp vs Sandage .) Arp also introduced us to our limitations sue to surface brightness considerations: We can’t see galaxies that are too small or that are too big (low Surface brightness)  THE LAMPPOST SYNDROME

  25. By the numbers: In a blue selected, magnitude limited, z=0 sample, 1/3 are E + S0, 2/3 are S + I 20% 15% 60% < 10% For Spirals ~ 1/2 A ~ 1/4 X ~ 1/4 B per unit volume is something else again.

  26. T Types -6 = cE 2 = Sab A = Unbarred -5 = E 3 = Sb X = Mixed -4 = E+ 4 = Sbc B = Barred -3 = S0- 5 = Sc -2 = S0 6 = Scd -1 = S0+ 7 = Sd 0 = S0/a 8 = Sdm etc. 1 = Sa 9 = Sm 10 = Im

  27. Quantitative Morphology Elliptical Galaxy Surface Brightness Profiles What is the shape of the galaxy? What is its integrated light? • Hubble Law (one of 4) I(r) = I0 (1 + r/r0)-2 I0 = Central Surface Brightness r0 = Core radius Problem(!) 4π∫ I(r) r dr diverges.

  28. (B) deVaucouleurs r1/4 Law I(r) = Ie e-7.67((r/re)1/4 - 1) a.k.a. 10-3.333333 re = effective radius = ½ light radius Ie = surface brightness at re Roughly, I0 = e7.67 Ie ~ 103.3333 Ie ~ 2100 Ie re ~ 11 r0 This function is integrable.

  29. (C) King Profile derived to fit isothermal spheres to globular star clusters, includes a tidal cutoff term with rc ~ r0, and rt = tidal radius I(r) = IK [(1+r2/rc2)– 1/2 - (1 + rt2/rc2)-1/2]2 (D) Oemler Truncated Hubble Law I(r) = I0 (1 + r/r0)-2 e–(r/b)2 (pre computers)

  30. Typical Numbers I0 ~ 15 – 19 magnitudes /sq arcsec in B <I0> ~ 17 m/sq” for Giant Elliptical Galaxies, r0 ~ 1 kpc rc ~ 10 kpc

  31. N4494

  32. King Profiles

  33. Spiral Galaxies Profiles are on average (over the spiral arms) Exponential Disks I(r) = IS e -r/rs Freeman (1970) found IS ~ 21.65 mag/sq” B for 28 of 36 galaxies rS ~ 1 – 5 kpc, function of Luminosity

  34. Spirals are Composite Spirals have both bulges (like E galaxies) and disks. From the deVaucouleurs Law LBulge = 2 ∫ I(r) πr dr = 7.22 π re2 Ie LDisk = 2π∫ IS e-r/rs r dr  D/B = 0.28 (rs/re)2 IS/Ie Disk to Bulge Ratio ∞ 0

  35. Sombrero (M104) HST

  36. Sombrero Spitzer

  37. Spiral Galaxy Structure What gives Spiral Galaxies their appearance? There are 2 main components (plus others less visible) Disk --- rotationally supported --- thickness is a function of the local vertical “pressure” vs gravity Spiral Pattern --- Three models Density Wave Tidal Interactions SPSF = self propagating star formation

  38. Density Waves  Lin’s “Grand Design” spirals (M81, M83) Interaction Induced Spirals  Good Looking spirals with Friends (M51) Self Propagating Star Formation --- detonation waves, SF driven by SF,  “Flocculent” Spirals

  39. M81Classic Grand DesignSpiral

  40. Another GD Spiral

  41. M51 Interacting System Optical Molecular Gas -CO

  42. M33 A Flocculent System

  43. NGC4414 another Flocculent S

  44. Spiral Structure Some Definitions: Number of Arms = m, most spirals have m=2, i.e. twofold symmetry Arm Orientation: Leading rotation Trailing

  45. Density Wave Theory Developed over many years by first Bertil Lindblad, then C.C. Lin, then Frank Shu: Quasi-stationary Spiral Structure Hypothesis (spiral pattern changes only slowly w. time) + Density Wave Hypothesis Pattern is a SF pattern driven by density change

  46. Follow the Mass Density Response of Stellar Disk Gravitational Field due to Stars & Gas + Density Response of Gaseous Disk || Total material needed to maintain the field = TOTAL RESPONSE

  47. Density Wave Models+ Bar Potential

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