Galactic Structure and Dynamics

1. Galactic Structure and Dynamics Andromeda

2. Mult-wavelength Far-Infrared map of M81 Bode’s Galaxy 12 million Lys Ursa Major constellation

3. Variety of Spiral Galaxies

6. Elliptical Galaxies

8. Types of Galaxies Spirals – nucleus, bulge, halo, spiral arms Barred Spirals – barred nucleus, …..”….. Ellipticals – various kinds of ellipticity, from near-circular E0 to highly oval and flat E7 (need to distinguish from edge-on view) – no disks, spiral arms, or dust lanes Irregulars – Not like spirals or ellipticals Hubble Classification – Tuning Fork Diagram

9. Ordinary Spirals Ellipticals Barred Spirals

10. Hubble Classification Ordinary Spirals – classified according to relative bulge strength and tightness of spiral arms - Sa: prominent bulge and tight but indistinct arms - Sb: less prominent bulge and looser arm structure - Sc: small bulge and loose and clearly seen arms i.e. from Sa to Sc, from tight to unwinding arms Barred Spirals – bar-shaped nucleus (jet??); as many as ordinary spirals; bar rotates like solid; spiral arms emerge from either end (SBa, SBb, SBc) Irregulars – chaotic structure, no systematic rotation, many dwarf irregular galaxies (classified as “dI”)

15. Barred Spirals: Powered by Rotating Jets

16. New Galaxy (General) Catalog (NGC)

18. Clusters of galaxies

19. Local Group of Galaxies Around Milky Way

20. Collision of Galaxies Galaxy-galaxy collision can induce gravitational tidal effects and lead to “starbursts” – rapid stellar formation

21. Twin galaxies: Spiral and Dwarf Whirlpool Galaxy disintegrates its small neighbor

22. Colliding Galaxies (Simulations)

23. Constant rotation Curves of Galaxies: Dark Matter

24. Properties of Galaxies

25. Stellar Birthrate: Ellipticals have older stars than spirals No significant star formation after 1 billion years Ongoing star formation

26. Distance Scale: Hubble’s law Hubble also discovered that the farther a galaxy is, the faster it is receding from us  the Universe is expanding  Big Bang ! Hubble’s Law: Velocity is proportional to distance v = H d (H – Hubble’s constant) H = 71 km/s/Mpc Observe the “redshift” (like Doppler shift) from the spectrum and determine the distance

28. Cosmological Distance Ladder • Several methods: - Trigonometric parallax (d = 1/p), Earth as baseline up to 100 pc (gd based) - 1 kpc (Hipparcos Satellite) - Spectroscopic parallax (spectral type of star gives absolute L on H-R diagram, up to 50-60 kpc - Cepheids and RR Lyrae, up to ~30-40 Mpc (using Hubble Space Telescope), out to about Virgo cluster - Tully-Fisher Relation: L is proportional to the Doppler width of the 21 cm H-line (proportional to mass and L) - Supernovae Ia up to a few hundred Mpc (using HST) • Each step calibrates the next one – “bootstrap method”

29. Observed Flux and Luminosity Distance Modulus: m – M = 5 Log (d/10) m – measured (apparent) magnitude M – absolute magnitude at 10 pc

30. H-R diagram can be used to ascertain Luminosity for any star of known spectral type and temperature, and therefore its distance

31. Cepheid Stars: Absolute Luminosity (M) from PeriodVariable apparent magnitude (m) with Time (days)Distance modulus: m-M = 5 log (d/10)  distance

32. Period-Luminosity Relation:Pulsating Cepheid, RR Lyrae Stars

33. The Hydrogen 21-cm radio map of the Sky and the Galaxy Tully-Fisher Relation: Width of 21-cm line, due to Doppler blue and redshifts, is proportional to mass of the galaxy, and therefore to intrinsic Luminosity L  Distance Modulus (m-M) gives d

34. Light Curves of Supernovae

35. Ho depends fit to data

36. Methods to determine the cosmological distance scale

37. Multiple images by gravitational lensing

38. Gravitational Lensing and Multiple Images Gravitational lensing can also be used to detect Dark Matter

39. Gravitational lensing of a quasar – two images a,b