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Chapter 15 Normal and Active Galaxies

Chapter 15 Normal and Active Galaxies. Andromeda M31 (Spiral) Galaxy with two companion elliptical galaxies. Similar to Milky Way galaxy. Galaxy types. Four types of galaxies have been identified by shape: Masses in units of Milky Way galaxy.

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Chapter 15 Normal and Active Galaxies

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  1. Chapter 15Normal and Active Galaxies Andromeda M31 (Spiral) Galaxy with two companion elliptical galaxies Similar to Milky Way galaxy

  2. Galaxy types Four types of galaxies have been identified by shape: Masses in units of Milky Way galaxy. • Elliptical galaxies: E0 to E7. E0 is spherical and E7 highly elliptical in shape. Contains very old, relatively less massive stars and have very little gas and dust. Most common galactic type. Mass 0.001 to 50. • Spiral galaxies: have central bulge and spiral arms. Have lots of gas and dust, mostly in the spiral arms. Mass 0.1 to 10. • Spiral bar SB have a bar attached to central bulge. • Milky Way galaxy is Spiral Bar • Irregular galaxies: no particular shape but has lots of gas and dust. Smaller in mass than spiral galaxies. About few per cent of galaxies are irregular. Mass < 0.01 • Large and Small Magellanic Clouds are Irregular Galaxies. • Active (peculiar) galaxies, such as quasars. Few in numbers.

  3. Pinwheel Galaxy Spiral NGC4546 Fig. 16-3, p.316

  4. Galaxies • Spiral, Elliptical and Active galaxies have black holes in the center. • First generation stars in Elliptical, central bulge of Spiral galaxies and globular clusters. • Second generation stars (e.g. Sun) in spiral arms and Irregular galaxies. • First generation stars mostly hydrogen and helium. • Second generation stars have heavier elements.

  5. Hubble Tuning Fork Types of Galaxies NGC = New General Catalogue Fig. 16-6b, p.318

  6. Hubble’s Galaxy Classification Spiral Bar galaxies The bar rotates as a solid!

  7. SmallMagellanic Cloud Irregular Galaxy Large Magellanic Cloud Irregular Galaxy SMA is farther than LMC Fig. 16-11a, p.320

  8. Active (peculiar) Galaxies: • Radio galaxies: Radio galaxies emit enormous amount of radio waves, typically much farther than the corresponding optical galaxy. • Radio galaxies usually are double lobed and have jets of particles • emitted from the nucleus of the galaxy. • When the jet of particles interacts with intergalactic matter, • radio waves are created. • Quasars: Quasars are near the edge of the Universe. Very bright. • Large redshift z > 0.1; small in size. • Seyfert galaxies are somewhat between quasars and normal galaxies. • Interacting galaxies are also classified as active. • From gravitational lensing of quasars by an in-between galaxy in our • line of sight, distances can be estimated and quasars are indeed • very far away. • Most galaxies have supermassive black holes in their center.

  9. Active Galaxy Dark matter? Radio galaxy Cygnus A Optical ^ Fig. 17-2, p.344

  10. Active Galactic Nuclei Solving the spectral problem introduces a new problem – quasars must be among the mostluminousobjects in the galaxy, to be visible over such enormous distances. Quasar Active galaxy

  11. Redshift z = Δλ/λ Quasar redshift z=0.17 p.342

  12. Quasar overexposed shows galaxy structure Fig. 17-19, p.353

  13. Quasars – Size is small ~ 0.1 ly. A large object can’t appear to fluctuate in brightness as rapidly as a smaller object. For example an object abruptly brightens at one instant. The wave emitted from the edge of the object takes longer to reach the observer than light from the near side of the object, because it has to travel farther. We don’t see the full variation until waves from all parts of the object reach us. Fig. 17-13, p.350

  14. Four quasars. Quasars appeared star like (i.e. points) but with very large Doppler shift. With bigger telescopes many quasars now have structure, such as spiral arms. Fig. 17-6, p.346

  15. Active Galactic Nuclei Seyfert galaxies. Similar to quasars but with spiral arms. Seyfert galaxiesresemble normal spiral galaxies, but their cores arethousandsof times more luminous:

  16. Interacting (Colliding) Galaxies • Galaxies do collide, but distance of stars are so big that stars do not collide with each other. • Computer models of colliding galaxies show that the spiral arms can break off forming irregular galaxies. The Mice NGC4676 Antennae galaxies

  17. Galactic Clusters • Most galaxies belong to clusters. • Number of galaxies in a cluster varies from 10 to 10,000. • Some small clusters are part of giant super clusters. • Such a group of galaxies are held together by its own gravity.

  18. Galaxy ClustersLocal Group • Local group has about 30 to 45 galaxies. • Two large Spiral galaxies, Milky Way and Andromeda galaxy. • Andromeda is 2.2 million light years away. • Large and Small Magellanic Clouds are companion galaxies of the Milky Way. LMC and SMC are small irregular galaxies.

  19. 15.2 The Distribution of Galaxies in Space Here is the distribution of galaxies within about1 Mpcof the Milky Way.

  20. The Distribution of Galaxies in Space Cepheid variablesallow measurement of galaxies to about 80 Mly away. Type I supernovaeall have about the same luminosity, as the process by which they happen doesn’t allow for much variation.

  21. Virgo Super Cluster has over 3,000 galaxies, Local group is in this cluster Fig. 16-17, p.323

  22. Deep field with red shifts (z): z = Δλ/λ Fig. 16-30, p.334

  23. Black Holes in Galactic Centers • Most likely all Elliptical and Spiral galaxies have central black holes. Some may have more than one black hole. • Milky Way 3 Million Solar mass • Andromeda M31 30 • M32 3 • NGC4261 400 • M87 3,000 • M104 1,000 • NGC 3377 100 Super massive Black Hole

  24. How do we know quasars are very far? Gravitational lensing Fig. 17-34, p.362

  25. Gravitational lensing of two quasars. Distance can be computed. Fig. 17-33, p.361

  26. Hubble’s Law Universal recession: all galaxies (with a couple of nearby exceptions) seem to be moving away from us, with theredshiftof their motion correlated with theirdistance: v/c = Δλ/λ.

  27. Expansion of the Universe v in km/sec Hubble plot in 1929. Fig. 16-27a, p.331

  28. Hubble’s Law These plots show the relation betweendistanceand recessional velocityfor the five galaxies in the previous figure, and then for a larger sample:

  29. Hubble’s Law up to c/3

  30. Edwin Hubble Hubble Law v = H0 × d H0 ~ 21 km/s/Mly H0 ~ 70 km/s/Mpc Basis of Big Bang Theory (Model) The value of H is not well known and varies between 50 and 80 km/s/Mpc. Fig. 16-5, p.317

  31. Universe has an edge Sloan Digital Sky Survey 2° Field Fig. 17-20a, p.353

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